論文 - 能崎　幸雄

Reversal of Spin-Torque Polarity with Inverting Current Vorticity in Composition-Graded Layer at the Ti/W Interface

Nakayama H., Horaguchi T., Uzuhashi J., He C., Sukegawa H., Ohkubo T., Mitani S., Yamanoi K., Nozaki Y.

Advanced Electronic Materials （Wiley）     2400797-1 - 2400797-9 2025年04月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2199-160X

　概要を見る

While compositional gradient-induced spin-current generation is explored, its microscopic mechanisms remain poorly understood. Here, the contribution of polarity of compositional gradient on spin-current generation is explored. A nanoscale compositional gradient, formed by in situ atomic diffusion of ultrathin Ti and W layers, is introduced between 10-nm-thick W and Ti layers. Spin-torque ferromagnetic resonance in ferromagnetic Ni95Cu5 deposited on this gradient reveals that a moderate compositional gradient suppresses negative spin torque from the spin Hall effect in W. In contrast, reversing the Ti/W stacking order, which inverts the gradient, suppresses positive spin torque from the orbital Hall effect in Ti. These findings suggest that the sign of spin torque is governed by the polarity of compositional gradient, providing a novel strategy for efficient spin-torque generation without relying on materials with strong spin or orbital Hall effect.

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Gyro-spintronic material science using vorticity gradient in solids

Nozaki Y., Sukegawa H., Watanabe S., Yunoki S., Horaguchi T., Nakayama H., Yamanoi K., Wen Z., He C., Song J., Ohkubo T., Mitani S., Maezawa K., Nishikawa D., Fujii S., Matsuo M., Fujimoto J., Maekawa S.

Science and Technology of Advanced Materials （Informa UK Limited）  26 （ 1 ） 2428153-1 - 2428153-39 2025年

査読有り,  ISSN  14686996

　概要を見る

We present a novel method for generating spin currents using the gyromagnetic effect, a phenomenon discovered over a century ago. This effect, crucial for understanding the origins of magnetism, enables the coupling between various macroscopic rotational motions and electron spins. While higher rotational speeds intensify the effect, conventional mechanical rotations, typically, below 10,000 RPM, produce negligible results comparable to geomagnetic fluctuations, limiting applied research. Our studies demonstrate that spin current generation comparable to that of rare metals can be achieved through atomic rotations induced by GHz-range surface acoustic waves and the rotational motion of conduction electrons in metallic thin films with nanoscale gradient modulation of electrical conductivity. These effects, termed the acoustic gyromagnetic effect and the current-vorticity gyromagnetic effect, are significant in different contexts. The acoustic gyromagnetic effect is notable in high-conductivity materials like aluminum and copper, which are more abundant than conventional spintronics materials with strong spin–orbit interactions (SOIs). Conversely, the current-vorticity gyromagnetic effect requires a large conductivity gradient to produce current vorticity efficiently. This is achieved by using composition gradient structures from highly conductive metals to poorly conductive oxides or semiconductors. Consequently, unlike traditional strong-SOI materials, we can create highly efficient spin current generators with low energy dissipation due to reduced Joule loss.

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Spatiotemporal visualization of a surface acoustic wave coupled to magnons across a submillimeter-long sample by pulsed laser interferometry

Maezawa K., Fujii S., Yamanoi K., Nozaki Y., Watanabe S.

Physical Review Applied （American Physical Society (APS)）  21 （ 4 ） 044047-1 - 044047-13 2024年04月

査読有り

　概要を見る

Surface acoustic waves (SAWs) coupled to magnons have attracted much attention because they allow for the long-range transport of magnetic information that cannot be achieved by magnon alone. We employed pulsed laser interferometry to visualize the entire spatiotemporal dynamics of a SAW that travels on a nickel (Ni) thin film and is coupled to magnons. It was possible to trace the coupling-induced amplitude reduction and phase shift that occurs as the SAW propagates over a distance of 0.4 mm. The observed changes are consistent with results obtained from conventional radio-frequency transmission measurements, which probe the total SAW absorption due to magnon-phonon coupling. This result verifies that our method can accurately capture the spatiotemporal dynamics of a SAW coupled to magnons across the entire length of the sample. Additionally, we validated our time-resolved profiles by comparing them with theoretical results that take the echo wave due to reflection into account. The impact of the echo wave is significant even when it has propagated over a distance of the order of millimeters. Our imaging results highlight the visualization of the long-range propagation of the SAW coupled to magnons and offer more information about the surface vibration profiles in such devices.

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Enhanced orbital torque efficiency in nonequilibrium Ru<inf>50</inf>Mo<inf>50</inf>(0001) alloy epitaxial thin films

Tang K., He C., Wen Z., Sukegawa H., Ohkubo T., Nozaki Y., Mitani S.

APL Materials （AIP Publishing）  12 （ 3 ） 031131-1 - 031131-7 2024年03月

査読有り

　概要を見る

Epitaxial thin films of fully nonequilibrium hcp-Ru50Mo50(0001) nanoalloys were prepared as a chemically disordered alloy, in which the intrinsic spin Hall effect is expected to be negligible. Structural analyses confirmed the epitaxial growth and atomic scale alloying of the films. In contrast to a tiny torque efficiency (ξDL) of ∼0.4% for Ru50Mo50/CoFeB, the ξDL for the Ru50Mo50/Ni heterostructure reached ∼30% with a long-range relaxation length. The apparent dependence of ξDL on the ferromagnetic layer can be attributed to the orbital Hall effect (OHE). Interestingly, a smaller ξDL was observed for Ru/Ni, suggesting that the nonequilibrium Ru50Mo50 enhances its OHE. Furthermore, the enhanced ξDL is maintained by inserting a Ru layer between the Ru50Mo50 and Ni layers, showing orbital transport through Ru. This finding illustrates potential applications of nonequilibrium nanoalloy films in spin orbitronics and contributes to getting insights into the understanding of the interrelationships between nanostructures and orbital transport properties.

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Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf> film with multi-domain epitaxy on single-crystalline LiNbO<inf>3</inf> substrate

Yamanoi K., Hase K., Komori S., Taniyama T., Nozaki Y.

APL Materials （AIP Publishing）  12 （ 2 ）  2024年02月

査読有り

　概要を見る

Y3Fe5O12 is one of the magnetic insulators that can realize high-speed and low-power-consuming spintronics devices. However, it is hard to prepare a high-quality Y3Fe5O12 film via a conventional sputtering process owing to its low crystalline texture, which leads to a crucial increase in the Gilbert damping constant. Moreover, a single crystalline Gd3Ga5O12 substrate, whose lattice constant is well matched with Y3Fe5O12, is indispensable to improve the crystallinity of the Y3Fe5O12 film. In this article, we demonstrated an epitaxial growth of multiple domains for a 30-nm-thick Y3Fe5O12 film by means of magnetron sputtering on a single crystalline 128° Y-X LiNbO3 substrate , which has been widely utilized in surface acoustic wave devices. From the pole figure of x-ray diffraction, an oblique epitaxial growth of Y3Fe5O12(400) is successfully observed on the 128° Y-X LiNbO3 substrate after a high-temperature post-annealing. The saturation magnetization is equivalent to the value of the epitaxial Y3Fe5O12 film on the Gd3Ga5O12 substrate. The relatively low effective Gilbert damping constant of 0.0039 also supports the high crystalline texture of the Y3Fe5O12 film. The developed growth technique will pave the way for the application of the Y3Fe5O12 film on magneto-acoustic devices.

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Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

Song J., He C., Scheike T., Wen Z., Sukegawa H., Ohkubo T., Nozaki Y., Mitani S.

Nanotechnology 34 （ 36 ） 365704-1 - 365704-10 2023年09月

査読有り,  ISSN  09574484

　概要を見る

The demonstration of the charge-to-spin conversion, especially with enhanced spin Hall conductivity, is crucial for the development of energy-efficient spintronic devices such as spin-orbit torque (SOT) based magnetoresistive random access memories. In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions consisting of Cu (1 nm)/Ru (1 nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency (ξ DL) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeable ξ DL of −2.2% and the insertion of Cu/Ru nanolayers at the interface can increase the ξ DL value to −3.7%. The former could be attributed to the interface spin-orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3∼5) × 105 ℏ 2 e Ω−1 m−1 in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. This work indicates that the interfacial control with hybrid nanolayer structures can extend the SOT-based materials to highly conductive metals, even with weak spin-orbit interactions, toward high stability, low cost, and low energy consumption for spintronic applications.

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A large modulation of spin pumping using magnetic phase transitions in single crystalline dysprosium

Yamanoi K., Sakakibara Y., Fujimoto J., Matsuo M., Nozaki Y.

Applied Physics Express （IOP Publishing）  16 （ 6 ） 063004-1 - 063004-6 2023年06月

査読有り,  ISSN  18820778

　概要を見る

We report a large modulation of spin pumping using temperature-induced magnetic phase transitions in c-axis oriented single crystalline dysprosium (Dy). From the temperature variation of the magnetic susceptibility, transitions from paramagnetic (PM) to ferromagnetic (FM) phases via antiferromagnetic (AFM) phase are clearly observed in the Dy. Unlike polycrystalline Dy, the spin pumping of both PM- and AFM-Dy are strongly suppressed owing to the increased non-dissipative backflow of spin current by the long-range spin transport, although two orders of magnitude difference exist between FM- and AFM-phases.

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Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films

Nakayama H., Horaguchi T., He C., Sukegawa H., Ohkubo T., Mitani S., Yamanoi K., Nozaki Y.

Physical Review B （AMER PHYSICAL SOC）  107 （ 17 ） 174416-1 - 174416-9 2023年05月

査読有り,  ISSN  24699950

　概要を見る

We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic Ni95Cu5 alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.

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Epitaxial Co<inf>2</inf>FeSi/LiNbO<inf>3</inf> multiferroic heterostructures with a low damping constant

Yamada S., Usami T., Komori S., Nagata S., Nozaki Y., Taniyama T., Hamaya K.

2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings （IEEE）  2023年

査読有り

　概要を見る

Piezoelectric LiNbO3 has been widely utilized to generate and detect spin waves in surface acoustic wave devices. Here we demonstrate an epitaxial Co-based Heusler alloy on a LiNbO3 128° Y-cut (LN-128Y) substrate by molecular beam epitaxy. Although there is no matching between the lattice length and symmetry, the insertion of a bcc metal buffer layer enables to grow L21 - ordered epitaxial Co2FeSi films on the LN-128Y substrate. The epitaxial Co2FeSi/LN- 128Y multiferroic heterostructures show a high saturation magnetization of ~1235 eμcc and a low damping constant of ~6 × 10-3. This study will open a way for an efficient electric-field control of the spin waves in surface acoustic wave devices.

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Optical Profiling of Surface-Acoustic-Wave Absorption due to Elastically Driven Ferromagnetic Resonance in Nickel

Maezawa K., Fujii S., Yamanoi K., Nozaki Y., Watanabe S.

2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings 2023年

　概要を見る

We optically characterized the local changes in the amplitude and phase of a surface vibration that are associated with the magnetoelastic effect. Pulsed laser interferometry was used to directly probe the amplitude and phase of a surface acoustic wave (SAW) propagating on a nickel thin film in a magnetic field, and a conversion from the angular momentum of the SAW to that of the macroscopic spin system was clearly observed. Pulsed laser interferometry opens the door to local probe and spatial mapping of magnon-phonon conversion in various magnetic materials, which can lead to further progress in fundamental and applied research related to magnetism.

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Spin current generation in highly conductive Ru/Cu epitaxial heterostructures

Wen Z., Song J., He C., Scheike T., Sukegawa H., Ohkubo T., Nozaki Y., Mitani S.

2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings 2023年

　概要を見る

Significant spin current generation from highly conductive materials is promising for spintronic applications, such as spin-orbit-torque magnetic random-access memories. In this work, we fabricated epitaxial Ru/Cu heterostructures with interface engineering where 1-nm-thick Ru and Cu layers were alternately deposited at the interface. The spin current generation in the heterostructures was evaluated by unidirectional spin Hall magnetoresistance and spin-torque ferromagnetic resonance. A sizable spin Hall efficiency (∼-2%) was achieved in the Ru/Cu sample with a sharp interface which may result from the interface spin filtering effect. Increased spin Hall efficiency (∼-4%) was observed in the interface-engineered samples which could be attributed to the intrinsic contribution from lattice distortion and local band structure near the interface. The effective spin Hall conductivity was estimated to be 3∼ 5 × 105h/2eΩ - 1m - 1, which is comparable to that of Platinum.

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Enhancement of room-temperature unidirectional spin Hall magnetoresistance by using a ferromagnetic metal with a low Curie temperature

Yamanoi K., Semizu H., Nozaki Y.

Physical Review B （American Physical Society (APS)）  106 （ 14 ） L140401-1 - L140401-5 2022年10月

査読有り,  ISSN  24699950

　概要を見る

The unidirectional spin Hall magnetoresistance (USMR) effect is useful to detect the direction of magnetization in a ferromagnetic metal/nonmagnetic metal bilayer, which is the typical geometry used in a spin-orbit torque switching device. In this Letter, we demonstrate the enhancement of the USMR effect by reducing the Curie temperature TC of the ferromagnetic (FM) layer in a FM/platinum bilayer. The USMR ratio was maximized when the thickness of each FM layer was consistent with the spin diffusion length. We found that the maximum USMR ratio can be doubled by replacing Ni81Fe19 (TC=854 K) with Ni85Cu15 (TC=527 K) as the FM. This enhancement of the USMR effect is attributed to an increase of electron-magnon scattering in accordance with Bloch law. We also found that the use of ferromagnets with face-centered-cubic structures, such as Ni, Ni81Fe19, and Ni85Cu15, increased the USMR effect relative to that of body-centered-cubic Fe.

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Temporal-offset dual-comb vibrometer with picometer axial precision

Iwasaki A., Nishikawa D., Okano M., Tateno S., Yamanoi K., Nozaki Y., Watanabe S.

APL Photonics （AIP Publishing）  7 （ 10 ） 106101-1 - 106101-8 2022年10月

査読有り

　概要を見る

We demonstrate a dual-comb vibrometer where the pulses of one frequency-comb are split into pulse pairs. We introduce a delay between two pulses of each pulse pair in front of the sample, and after the corresponding two consecutive reflections at the vibrating sample surface, the initially introduced delay is canceled by a modified Sagnac geometry. The remaining phase difference between the two pulses corresponds to the change in the axial position of the surface during the two consecutive reflections. The Sagnac geometry reduces the effect of phase jitter since both pulses propagate through nearly the same optical path (in opposite directions), and spurious signals are eliminated by time gating. We determine the amplitude of surface vibration on a surface-acoustic-wave device with an axial precision of 4 pm. This technique enables the highly accurate determination of extremely small displacements.

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Quantitative Measurement of Absolute Displacement of Surface Acoustic Wave with ~26 pm Axial Resolution Using Time-Division Dual-Comb Interferometry

Iwasaki A., Nishikawa D., Okano M., Tateno S., Yamanoi K., Nozaki Y., Watanabe S.

2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings 2022年

　概要を見る

We demonstrate a quantitative evaluation of absolute displacement of surface acoustic wave by the time-division dual-comb interferometry with the Sagnac geometry. Due to an ultrahigh stability of the Sagnac geometry, achieved resolution is -26 pm.

Quantitative Measurement of Absolute Displacement of Surface Acoustic Wave with ~26 pm Axial Resolution Using Time-Division Dual-Comb Interferometry

Iwasaki A., Nishikawa D., Okano M., Tateno S., Yamanoi K., Nozaki Y., Watanabe S.

Optics InfoBase Conference Papers 2022年

　概要を見る

We demonstrate a quantitative evaluation of absolute displacement of surface acoustic wave by the time-division dual-comb interferometry with the Sagnac geometry. Due to an ultrahigh stability of the Sagnac geometry, achieved resolution is ~26 pm.

Einstein-de Haas phase shifts in surface acoustic waves

Tateno S., Kurimune Y., Matsuo M., Yamanoi K., Nozaki Y.

Physical Review B （AMER PHYSICAL SOC）  104 （ 2 ） L020404-1 - L020404-5 2021年07月

査読有り,  ISSN  24699950

　概要を見る

We demonstrate the phase shift of the Rayleigh-type surface acoustic wave (RSAW) in a ferromagnetic Ni81Fe19 film based on the gyromagnetic Einstein-de Haas (EdH) torque that can be attributed to the back action of spin-wave excitation. The EdH torque modulates the transverse velocity of the bulk acoustic wave that causes the bipolar phase shift of RSAW. When compared with a magnetoelastic torque, the phase shift can be more prominently enhanced by increasing the frequency. The gyromagnetic torque in the RSAW paves the way for controlling spin-mechatronics devices without magnetoelastic torque which is specific to a certain material.

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Experimental method for quantitative evaluation of nonlinear magnetization dynamics

Okano G., Nozaki Y.

IEEJ Transactions on Fundamentals and Materials （Institute of Electrical Engineers of Japan）  141 （ 2 ） 99 - 104 2021年02月

査読有り,  ISSN  03854205

　概要を見る

We have developed an experimental technique to investigate a nonlinear magnetization dynamics resonantly excited by strong microwave fields. In this technique, a magnetization switching was observed when a sub-nanosecond wide pulsed field was applied to the ferromagnetic resonance-excited ferromagnets. Such a cooperative switching with simultaneous application of microwave- and pulsed-fields can evaluate an effective energy barrier for magnetization switching in various nonlinear magnetization dynamics. In this review, we show the experimental results on (1) the temporal evolution of the energy barrier in the transient of magnetization precession growth and (2) the observation of saddle-node bifurcation in the microwave-excited nonlinear magnetization dynamics.

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Highly nonlinear frequency-dependent spin-wave resonance excited via spin-vorticity coupling

Yuki Kurimune, Mamoru Matsuo, Sadamichi Maekawa, Yukio Nozaki

Physical Review B （American Physical Society (APS)）  102 （ 17 ） 174413-1 - 174413-7 2020年11月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2469-9950

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Electrical evaluation of the alternating spin current generated via spin-vorticity coupling

Shoma Tateno, Genki Okano, Mamoru Matsuo, Yukio Nozaki

Physical Review B （American Physical Society (APS)）  102 （ 10 ） 104406-1 - 104406-9 2020年09月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2469-9950

　概要を見る

In many interacting-electron systems, the microscopic spin angular momentum of electrons is conserved along with the macroscopic angular momentum in electrical current flows, i.e., vorticity. Such spin-vorticity coupling expands the choice of materials for spintronics devices. In this paper, we evaluate the magnitude of an alternating spin current generated by the spin-vorticity coupling with a gigahertz-order surface acoustic wave in a Cu thin film. We measure the gigahertz alternating spin current by an electrical method based on the inverse spin-Hall effect. From the amplitude of the spin current, we can determine the conversion efficiency of the angular momentum between local lattice rotation and electron spin in the Cu film. The conversion efficiency is four orders of magnitude larger than the case of spin current generation via kilohertz-order vorticity in turbulent flow of liquid mercury [M. Matsuo et al., Phys. Rev. B 96, 020401(R) (2017)]. Such a huge conversion efficiency is attributable to a smaller inconsistency of energy scale between lattice rotation and electron spin than the case of liquid vorticity.

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Highly accurate evaluation of spin-torque efficiency by measuring in-plane angular dependence of spin-torque ferromagnetic resonance

Horaguchi T., Matsuo M., Nozaki Y.

Journal of Magnetism and Magnetic Materials （Journal of Magnetism and Magnetic Materials）  505   166727-1 - 166727-5 2020年07月

査読有り,  ISSN  03048853

　概要を見る

© 2020 Spin-torque ferromagnetic resonance (ST-FMR) is a powerful tool to evaluate spin-torque efficiency (ξFMR), the efficiency of current-induced torque in metallic bilayers consisting of ferromagnetic and nonmagnetic materials. In general, ξFMR can be evaluated from the amplitude ratio between symmetric and anti-symmetric components of the ST-FMR spectrum. However, the ratio is also affected by an unnecessary magnetic field owing to the asymmetric alternating current flow used to excite the ST-FMR. In this article, we demonstrate that ξFMR can be precisely evaluated from the full-angular dependence of the ST-FMR spectrum even though the distribution of alternating current flow is highly asymmetric.

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Observation of Gyromagnetic Spin Wave Resonance in NiFe Films

Kurimune Y., Matsuo M., Nozaki Y.

Physical Review Letters （Physical Review Letters）  124 （ 21 ） 217205-1 - 217205-6 2020年05月

査読有り,  ISSN  00319007

　概要を見る

© 2020 American Physical Society. This Letter demonstrates spin wave resonance (SWR) owing to the gyromagnetic effect by propagating a Rayleigh-type surface acoustic wave (R-SAW) through ferromagnetic thin films. The SWR amplitude in a NiFe film shows a higher-order frequency variation than in a magnetoelastic Ni film. This frequency dependence is well understood in terms of the presence of a gyromagnetic field attributable to the local lattice rotation in the R-SAW. From the frequency dependence of the SWR amplitude, the gyromagnetic SWR could be separated from another SWR caused by a magnetoelastic effect of the ferromagnet.

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Highly nonreciprocal spin waves excited by magnetoelastic coupling in a ni / si bilayer

Tateno S., Nozaki Y., Nozaki Y.

Physical Review Applied （Physical Review Applied）  13 （ 1 ） 034074-1 - 034074-5 2020年03月

査読有り

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© 2020 American Physical Society. We demonstrate a largely enhanced nonreciprocal propagation of spin waves (SWs) magnetoelastically excited in Ni/Si bilayer films. The nonreciprocity is attributed to the shear component of the strain tensor, which can be enlarged by increasing the thickness of the Si layer. By evaporating a 400-nm-thick Si layer on a Ni film, we enhanced the nonreciprocal ratio by up to 1200%. This finding paves the way for rectification of SWs in magnonic devices.

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Spin waves parametrically excited via three-magnon scattering in narrow NiFe strips

Okano G., Nozaki Y.

Physical Review B （Physical Review B）  100 （ 10 ） 104424-1 - 104424-10 2019年09月

査読有り,  ISSN  24699950

　概要を見る

© 2019 American Physical Society. Three-magnon scattering can be used to evaluate the lowest frequency of the magnon band in a ferromagnet. Both the ferromagnetic-resonant (FMR) frequency fFMR and the lowest frequency of the magnon band fmin in narrow-shaped NiFe strips were electrically measured using the anisotropic-magnetoresistance effect. The comparison with a micromagnetic simulation shows that fmin of the magnon band can be controlled independent of fFMR by varying the width w and thickness t of the NiFe strip while maintaining a constant t/w ratio. In addition, we found that the frequency difference, fFMR-fmin, can be greatly increased in thicker NiFe strips. Our results show that narrow-shaped ferromagnets allow us to tune the magnon-band structures by varying their w and t. This ability is important for designing magnon circuits in integrated magnonic devices and for improving the quantitative study on the Bose-Einstein condensation of magnons.

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Nonreciprocal Spin Current Generation in Surface-Oxidized Copper Films

Okano G., Matsuo M., Ohnuma Y., Maekawa S., Nozaki Y.

Physical Review Letters （Physical Review Letters）  122 （ 21 ） 217701-1 - 217701-6 2019年05月

査読有り,  ISSN  00319007

　概要を見る

© 2019 American Physical Society. We experimentally demonstrate the nonreciprocal generation of spin current (Js) in a surface-oxidized copper film. The efficiency of conversion is at least 320 times larger than the inverse conversion. This nonreciprocity is due to a novel type of Js generation, which relies on the transfer of angular momentum from the velocity field of free electrons. A gradient in the electrical mobility in the film produces vorticity in the in-plane drift velocity of the free electrons. The inverse process can hardly occur when Js is collinear with the gradient in the electrical mobility.

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Evaluating the nonadiabatic spin-transfer torque using coupled oscillation of magnetic vortices

Horaguchi T., Tanazawa T., Nozaki Y.

Physical Review B （Physical Review B）  98 （ 6 ）  2018年08月

査読有り,  ISSN  24699950

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© 2018 American Physical Society. In this paper, we detect the coupled oscillation of magnetic vortices in Ni81Fe19 gourd-shaped thin films electrically to evaluate the nonadiabatic spin-transfer torque (STT) coefficient β, which is important for understanding a variety of STT-related phenomena. We excite a translational mode in coupled magnetic vortices by applying an alternating electrical current that causes both STT and Oersted field torque. Since the coupled oscillation modes due to the STT and Oersted field torque have totally different eigenfrequencies, the coupled oscillation spectrum can be used to evaluate β, which is generally difficult to distinguish from the Oersted field contributions. Based on the ratio between the amplitudes of the spectrum's Lorentzian and anti-Lorentzian components, the value of β is found to be 0.085±0.016, which is 4.3 times larger than the Gilbert damping constant α.

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Excitation of Ferromagnetic Resonance Using Surface Acoustic Waves

Nozaki Y., Yanagisawa S.

Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) （Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi)）  204 （ 3 ） 3 - 9 2018年08月

査読有り,  ISSN  04247760

　概要を見る

© 2018 Wiley Periodicals, Inc. Mechanical rotation of a crystal lattice in ferromagnetic materials can be energetically coupled with its magnetization via magnetoelastic coupling or spin rotation coupling. Surface acoustic wave (SAW) in piezoelectric materials is one of the promising candidates to realize the mechanical excitation of magnetization dynamics. In order to understand the mechanical rotation induced magnetization dynamics quantitatively, we examined the ferromagnetic resonance in an Ni film using a SAW in a LiNbO3 substrate. By decreasing a period of interdigital transducer as short as 4 μm which is one-fifth of the previous work by Weiler [M. Weiler and co-workers, Elastically driven ferromagnetic resonance in Nickel thin films. Phys Rev Lett 106, 117601 (2011)], the fundamental frequency of SAW could be higher than 800 MHz. From the dependence of microwave absorption on the angle between the magnetization and the wave vector of SAW, it was confirmed that the Rayleigh type SAW, which was significant to obtain a large mechanical coupling with the magnetization, was dominantly excited in the 800-MHz-SAW device.

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Modulation of magnetization dynamics in an epitaxial Heusler ferromagnet due to pure spin current in a laterally configured structure

Oki S., Sasaki Y., Kasatani Y., Yamada S., Mizukami S., Nozaki Y., Hamaya K.

Journal of Physics Condensed Matter （Journal of Physics Condensed Matter）  30 （ 25 ）  2018年05月

査読有り,  ISSN  09538984

　概要を見る

© 2018 IOP Publishing Ltd. Using a laterally configured structure, we demonstrate modulation of the magnetization dynamics of an epitaxial Heusler ferromagnet, Fe3Si, by nonlocally injecting pure spin currents. From the ferromagnetic resonance signals, the effective Gilbert damping constant () of the epitaxial Fe3Si nanomagnet is estimated to be ∼0.003 at room temperature. By using the lateral and nonlocal spin injection, the value of the epitaxial Fe3Si nanomagnet can be modulated from 0.0034 to 0.0024. This study will open a way for control of the magnetization dynamics of high-performance ferromagnetic Heusler alloys due to pure spin currents even in laterally configured structures.

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Evaluation of the effective potential barrier height in nonlinear magnetization dynamics excited by ac magnetic field

Okano G., Nozaki Y.

Physical Review B （Physical Review B）  97 （ 1 ）  2018年01月

査読有り,  ISSN  24699950

　概要を見る

© 2018 American Physical Society. An alternating current (ac) magnetic field or spin current can reduce the switching field of a ferromagnet through resonance excitation of a large-angle precession of magnetization. The nonlinear magnetization dynamics of this switching scheme completely differ from the general ferromagnetic resonance phenomenon, which is linearly excited by a small ac magnetic field. To understand these dynamics, it is necessary to evaluate the effective potential barrier height for switching, ΔUeff. However, most previous studies have measured the consequent precession angle in the nonlinear dynamics by magneto-optical methods and/or by applying a magneto-resistive effect. Here, we applied the cooperative switching method, which evaluates the ΔUeff of the nonlinear dynamics under a sub-ns-wide magnetic field impulse, and observed a nontrivial reduction of ΔUeff in a submicron-wide NiFe strip. The strong reduction of ΔUeff under a negative magnetic field was caused by a saddle-node bifurcation in the nonlinear dynamics. In a micromagnetics simulation, we also confirmed that the magnetization is nonuniformly excited at the shallowest ΔUeff.

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Micromagnetic Simulation of Microwave-Assisted Magnetization Switching Process for Granular Films

Terumitsu Tanaka, Yukio Nozaki, Kimihide Matsuyama

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  53 （ 11 ）  2017年11月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

Microwave-assisted magnetization switching (MAS) processes for granular films were demonstrated by time integration of the Landau Lifshitz Cilbert equation. At low microwave frequencies, hysteresis loops become narrower, and at higher frequencies, an extra step occurs in the curves. In the case when the extra step occurs, saturation field increases to be comparable to that for non-MAS case, although switching field decreases. The occurrence of the extra step possibly originates from "unstable switching process" predicted by Bertotti et al., and the magnetization contour maps indicated large un-switched agglomerates remains when MATS proceeds through the unstable switching process. The unstable switching processes are also observed even when dc incident angles are large.

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Spin Current Generation Using a Surface Acoustic Wave Generated via Spin-Rotation Coupling」

D. Kobayashi, T. Yoshikawa, M. Matsuo, R. Iguchi, S. Maekawa, E. Saitoh, Y. Nozaki

Physical Review Letters （The American Physical Society）  119 （ 7 ） 077202-1 - 077202-5 2017年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0031-9007

　概要を見る

We demonstrate the generation of alternating spin current (SC) via spin-rotation coupling (SRC) using a surface acoustic wave (SAW) in a Cu film. Ferromagnetic resonance caused by injecting SAWs was observed in a Ni-Fe film attached to a Cu film, with the resonance further found to be suppressed through the insertion of a SiO2 film into the interface. The intensity of the resonance depended on the angle between the wave vector of the SAW and the magnetization of the Ni-Fe film. This angular dependence is explicable in terms of the presence of spin transfer torque from a SC generated via SRC.

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表面弾性波を用いた強磁性共鳴の励起

能崎 幸雄, 柳澤 翔吾

電気学会論文誌Ａ（基礎・材料・共通部門誌） （電気学会）  137 （ 7 ） 386 - 391 2017年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0385-4205

Circularly Polarized Magnetic Field Generated by Two Microfabricated Crossed Coplanar Waveguides」

I. Kan, Y. Soeno, T. Roppongi, Y. Nozaki

Applied Physics Letters （The American Institute of Physics）  110 （ 20 ） 202404-1 - 202404-4 2017年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0003-6951

　概要を見る

We generate a circularly polarized (CP) magnetic field using two crossed coplanar waveguides (TCCWs). By using the CP field, we selectively excite a ferromagnetic resonance between positively and negatively magnetized Co/Ni multilayers. The CP field arises from a superposition of Ampere fields generated by microwaves orthogonally propagating along the crossed arms of the TCCWs. The polarity of the magnetic field can be tuned continuously from circular to linear by exploiting a phase delay between the orthogonal microwaves. From a local measurement of the magneto-optical Kerr effect, we also find that the ellipticity of the CP field is distributed over the intersection of the TCCWs. These results indicate that TCCWs have great potential as CP-field generators that can be integrated into micron-scale electrical devices. Published by AIP Publishing.

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Magneto-optic Kerr effect CCD imaging with polarization modulation technique

Satoru Nakayama, Makoto Okano, Yukio Nozaki, Shinichi Watanabe

AIP ADVANCES （AMER INST PHYSICS）  7 （ 5 ）  2017年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2158-3226

　概要を見る

We have developed a magneto-optic Kerr effect (MOKE) imaging system with a charge-coupled-device (CCD) camera by using the rotating compensator technique. We chose optimal conditions of the rotation frequency of the compensator with stable rotation along with a CCD camera frame rate that allowed precise control of the exposure timing in order to link with the angle of the compensator. Precise timing management of the CCD exposure enables us to carry out repeated experiments, which greatly improves the signal-to-noise ratio of the longitudinal MOKE signal. We applied the technique to the material characterization of the Ni-81 Fe-19 thin film and its microstructure, and succeeded in evaluating the spatial variation of the complex magneto-optic constant Q of the sample. Because of its attractive advantages such as high-speed and compactness, the present method provides a novel platform for investigating the domain structures in various magnetic materials. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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交差型コプレーナ線路上に生じた円偏向磁場の空間分布測定

菅　逸樹, 能崎 幸雄

電気学会研究会資料 （電気学会）  MAG-16-217   1-6 2016年12月

研究論文（その他学術会議資料等）, 共著

FMRスペクトル形状によるマイクロ波アシスト磁化反転の安定性の定量的解析

能崎 幸雄, 田中輝光

電気学会研究会資料 （電気学会）  MAG-16-230   1-6 2016年12月

研究論文（その他学術会議資料等）, 共著

Spin-transfer-torque-assisted magnetization reversal in spin-valve strips using the spin-pumping effect

TAKAHASHI Mao, NOZAKI Yukio

Applied Physics Express （Japanese Society of Applied Physics）  9 （ 6 ） 063002-1 - 063002-4 2016年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-0778

　概要を見る

The modulation of a switching field by a spin-transfer torque generated by the spin-pumping effect is demonstrated in spin-valve strips. A spin current pumped into a spin valve prefers an antiparallel configuration of magnetization, so that the hysteresis loop of a soft magnetic layer is shifted by applying an alternating-current magnetic field with a frequency that matched the resonant condition of a hard magnetic layer. Furthermore, we confirmed that an alternating spin current generated by the spin pumping in the hard magnetic layer produces an orthogonal magnetic torque that can reduce the coercive field of the soft magnetic layer.

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Microwave-assisted magnetization reversal using transient precession of magnetization in permalloy hexagons

OKANO Genki, NOZAKI Yukio

Applied Physics Express （Japanese Society of Applied Physics）  9 （ 6 ） 063001-1 - 063001-4 2016年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-0778

　概要を見る

Microwave-assisted magnetization reversal utilizing a transient precession of magnetization was demonstrated in a permalloy hexagon by applying a 25-ns-wide microwave field and a 500-ps-wide pulsed field with a tunable delay to the microwave field. The switching field in a combination of these two fields becomes smaller than that in only the microwave field, and this additional reduction in switching field oscillates relative to the delay time. From the comparison with the results of micromagnetic simulations, we found that the oscillatory behavior is attributed to the beats in transient precession that occurs in the early stage of microwave-field-induced magnetization excitation.

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Current-driven antivortex core resonance measured by the rectifying effect

GOTO Minori, NOZAKI Yukio

AIP Advances （AIP）  6 （ 2 ） 025313-1 - 025313-6 2016年02月

研究論文（学術雑誌）, 共著, 査読有り

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Real-space observation of magnetic vortex core gyration in a magnetic disc both with and without a pair tag

A. Yamaguchi, H. Hata, M. Goto, M. Kodama, Y. Kasatani, K. Sekiguchi, Y. Nozaki, T. Ohkochi, M. Kotsugi, T. Kinoshita

Japanese Journal of Applied Physics （IOP Science）  55 （ 2 ） 023002-1 - 023002-13 2016年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-4922

　概要を見る

We demonstrate the time-resolved real-space observation of vortex gyration in a magnetic circular disc by X-ray magnetic circular dichroism photoemission microscopy at the SPring-8 beamline BL25SU, both with and without an additional structure called a pair tag, which serves to control the magnetic curling direction. By comparing the gyration orbits of the vortices, we found that the gyration properties are dependent on the presence of the additional structure in spite of the discs having the same diameter. Furthermore, we reproduced the vortex gyration by micromagnetic simulation. The confinement potential of the vortex can be controlled by the additional structure.

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パラメトリック励起スピン波を活用した磁化反転実験

岡野 元基, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人 日本物理学会）  71   892 - 892 2016年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

<p>ある閾値強度よりも大強度のマイクロ波印加の下では、Suhl instabilityという不安定性が現れ、パラメトリックにスピン波が励起される。一方で大振幅歳差運動を励起して磁性体の保磁力を低減するマイクロ波アシスト磁化反転(MAMR)という技術が注目されている。本研究では、ナノスケール金属磁性体中でのSuhl instabilityの性質について調べ、パラメトリックに励起されたスピン波を活用したMAMR実験を行った。その結果、不安定性がMAMRにおいてどのような役割を果たすのかについて明らかにした。</p>

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21pPSA-58 CCD カメラを用いたNiFe薄膜構造の磁気光学カ-効果の定量的測定

中山 智, 岡野 真人, 能崎 幸雄, 渡邉 紳一

日本物理学会講演概要集 （一般社団法人日本物理学会）  71   1617 - 1617 2016年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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19aAU-5 磁気渦対の連成共振における磁気トルクとスピントルクの分離

棚澤 友幾, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  71   1000 - 1000 2016年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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19aAU-2 NiFe薄膜パターンにおける磁化反転の動的準安定状態に関する研究

岡野 元基, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  71   997 - 997 2016年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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交差型コプレーナ線路を用いた回転磁場の生成と強磁性共鳴の誘引

菅 逸樹, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人 日本物理学会）  71   891 - 891 2016年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

<p>酸化シリコン基板上に二つのコプレーナ線路を交差させた交差型コプレーナ線路とCo/Ni多層膜を蒸着した。この交差型コプレーナ線路に二方向からマイクロ波を入力し、位相変調器を用いて相対的な位相差を変えることで、生成される交流磁場の偏向を制御した。生じた交流磁場を用いて強磁性共鳴の測定を行ったところ、磁場の偏向を回転させることで磁化の方向について選択的に共鳴が励起された様子が観測された。</p>

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中間層により交換結合を制御したCo-Cr-Pt基ECC媒体のマイクロ波アシスト磁化反転

鈴木 翔子, 葛西 伸哉, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人 日本物理学会）  71   822 - 822 2016年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

<p>磁気異方性エネルギーの異なるCo-Cr-Pt基グラニュラー膜を積層したECC(exchanged coupled composite)媒体は、膜厚方向にスピン波が誘引されると磁化反転磁場が減少する。本研究では、ECC媒体の層間交換結合を中間層の膜厚によって制御した媒体を作製し、そのマイクロ波アシスト磁化反転特性を測定した。特に、磁化反転アシスト効果が最大化する周波数、およびアシスト効果に必要な交流磁場強度の閾値の中間層膜厚依存性を調べた。</p>

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Crystallographic anisotropy of intrinsic Gilbert damping for single crystalline Fe film

KASATANI Yuichi, NOZAKI Yukio

Journal of Magnetics Society of Japan （Magnetics Society of Japan）  39 （ 6 ） 221 - 226 2015年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-2924

　概要を見る

We experimentally investigated the crystallographic anisotropy of the intrinsic Gilbert damping constant in single crystalline Fe(001) film deposited on MgO(001) substrate. The frequency-domain ferromagnetic resonance (FMR) spectrum was measured at given external magnetic fields via a vector network analyzer. From the field-domain FMR linewidth obtained as a function of resonant frequency, the intrinsic Gilbert damping constants along the crystallographic axes in the (001) plane were successfully obtained by evaluating the extrinsic influence of two magnon scattering and inhomogeneity. A four-fold crystalline anisotropy of the intrinsic Gilbert damping constant, similar to the magnetic crystalline anisotropy in the (001) plane, was clearly observed. Furthermore, we found that the intrinsic Gilbert damping constant along the easy axis was smaller than that along the hard axis.

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Microwave-Assisted Magnetization Reversal in Exchange-Coupled Composite Media Using Linearly Polarized Microwave Fields

NOZAKI Yukio, KASAI Shinya

IEEE Transactions on Magnetism （IEEE）  52 （ 2 ） 3100207-1 - 3100207-7 2015年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0018-9464

　概要を見る

We have experimentally demonstrated a microwave-assisted magnetization reversal (MAMR) in exchange-coupled composite (ECC) media using the linearly polarized microwave fields generated by an electrically shorted coplanar waveguide. The MAMR frequency exhibiting a maximum reduction of coercive field can be decreased using 16 nm-thick ECC media without the suppression of the thermal stability of magnetization. The threshold amplitude of microwave field required for the successful MAMR is only 3% of the anisotropy field of the medium. A splitting of ferromagnetic resonance spectrum, which suggests an appearance of stochastic MAMR, can be observed after applying microwave fields. The stochastic MAMR gives rise to the threshold behavior in the condition of microwave field amplitude needed for MAMR.

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Spin transfer torque in lateral spin-valve structure evaluated from field-excited ferromagnetic resonant linewidth.

Y. Nozaki, S.D. Watanabe, T. Kobayashi, and T. Tanazawa

Applied Physics Express （The Japan Society of Applied Physics）  8 （ 4 ） 043001 (4 pages) 2015年03月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-0778

　概要を見る

Modulation of ferromagnetic resonance (FMR) linewidth owing to a spin transfer torque (STT) caused by the absorption of a pure spin current in a permalloy nanowire is demonstrated. To exclude the STT induced by the spin-polarized current, the pure spin current was produced using a lateral spin-valve structure. Self-homodyne FMR detection without applying an external sense current was used for minimizing the influence of Joule heating on the FMR linewidth. The linear variation of the FMR linewidth caused by the STT was clearly observed when the electrical current generating the pure spin current was below 1 mA. (C) 2015 The Japan Society of Applied Physics

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Criteria for Electric Determination of Antivortex Creation in Ferromagnetic Thin Film

M. Goto, Y. Nozaki, and K. Sekiguchi

Japanese Journal of Applied Physics （The Japan Society of Applied Physics）  54 （ 2 ） 023001 (4 pages) 2015年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-4922

　概要を見る

Antivortex creation in a cross-shaped wire was demonstrated by using magnetoresistance and magnetic force microscopy measurements. The magnetization process was stochastic and exhibited a wide variety of magnetoresistance curves. By developing a conventional method, we have achieved electrical determination criteria to distinguish antivortex creation from many other magnetization states. The electrical criteria provide a simple method without large-scale apparatus and promote further experiments such as spin-current driven antivortex dynamics. (C) 2015 The Japan Society of Applied Physics

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マイクロ波アシスト磁化反転特性と磁化の熱安定性の数値計算(ヘッド・スピントロニクス,一般)

田中 輝光, 能崎 幸雄, 松山 公秀

映像情報メディア学会技術報告 （一般社団法人 映像情報メディア学会）  39   27 - 32 2015年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

単層のCoPt系グラニュラー媒体を例に,実測とマイクロマグネティック計算におけるマイクロ波アシスト磁化反転特性をSharrockの式を通して比較した.マイクロマグネティック計算によって得られたマイクロ波アシスト時のスイッチング磁界からマイクロ波印加によるエネルギー障壁の減少値を見積もり,Sharrockの式を用いてマイクロ波アシスト時の磁気余効計算を行った.その結果,実測では低周波領域でマイクロ波アシストの効果がみられないが,これは磁気余効によるスイッチング磁界の減少がマイクロ波アシストによるスイッチング磁界の減少分よりも大きいため測定結果に表れていないことが分かった.また,計算結果と実測結果との不一致の原因はマイクロマグネティック計算で示される不安定な磁化反転領域に当たる周波数帯が実測における最適周波数であること,そしてマイクロ波によるアシストエネルギーが逆磁界大きさによって変化するという複雑な関係があることが原因であると推測される.

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24aCN-8 強磁性体磁気渦構造への高強度テラヘルツ光パルス照射実験

曽澤 将昇, 立崎 武弘, Ropagnol Xavier, Razavipour Hadi, 尾崎 恒之, Cooke David, 能崎 幸雄, 渡邉 紳一

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   1625 - 1625 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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23pAD-6 ホイスラー合金Co_2FeSi薄膜におけるGilbertダンピング定数の異方性

笠谷 雄一, 山田 晋也, 伊藤 博介, 宮尾 正信, 浜屋 宏平, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   1201 - 1201 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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21pPSA-29 強磁性交差細線における磁気反渦の共鳴

後藤 穣, 棚澤 友幾, 関口 康爾, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   1102 - 1102 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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21pPSA-25 弾性表面波を用いたNi薄膜パターンの強磁性共鳴誘引

柳澤 翔吾, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   1098 - 1098 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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21pPSA-16 スピンポンピング効果を用いたスピン流アシスト磁化反転実験

高橋 真央, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   1089 - 1089 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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21aPS-62 ナノ秒パルス重畳マイクロ波を用いたNiFeパターンの磁化反転実験

岡野 元基, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   996 - 996 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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21aPS-53 強磁性薄膜パターンにおける磁気渦対の生成と観察

棚澤 友幾, 後藤 穣, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   987 - 987 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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16pPSA-36 サブナノ秒パルス磁場を用いたマイクロ波アシスト磁化反転の非線形ダイナミクスに関する研究

岡野 元基, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   848 - 848 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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16pPSA-25 スピンポンピング効果を用いたスピン流アシスト磁化反転実験2

高橋 真央, 能崎 幸雄

日本物理学会講演概要集 （一般社団法人日本物理学会）  70   837 - 837 2015年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  2189-079X

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巨大磁気抵抗効果を用いたスピン流アシスト効果の検出(ヘッド・スピントロニクス,一般)

高橋 真央, 能崎 幸雄

映像情報メディア学会技術報告 （一般社団法人 映像情報メディア学会）  39   7 - 10 2015年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

強磁性体俳磁性体/強磁性体の擬スピンバルブ3層膜において、一方の強磁性体が共鳴する周波数のマイクロ波を印加してスピンポンピング由来のスピン流を生成し、そのスピン流によるスピントランスファートルクをもう一方の強磁性層に作用させる実験を行った。巨大磁気抵抗効果を利用することにより、マイクロ波印加に伴う各強磁性層の保磁力の変化を調べた。保磁力のマイクロ波周波数依存性を調べた結果、磁化を共鳴させた磁性層にマイクロ波アシスト磁化反転による保磁力低減効果が見られた。これに対し、スピン流が注入された先の強磁性層の保磁力は、スピンポンピング由来のスピン流が最も大きく生成される周波数で極小となることがわかった。

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ナノ秒パルス印加下でのマイクロ波アシスト磁化反転速度に関する研究

岡野元基, 能崎 幸雄

電気学会研究会資料 （電気学会）  MAG-14-226   1-6 2014年12月

研究論文（その他学術会議資料等）, 共著

Cooperative microwave-assisted magnetization reversal with pulsed fields in 2-µm-wide nickel–iron wires at nanosecond time scales

G. Okano, Y. Nozaki

Applied Physics Express （The Japan Society of Applied Physics）  8 （ 1 ） 013001 (4 pages) 2014年12月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-0778

　概要を見る

The switching dynamics of nickel iron wires (length, 100 mu m; width, 2 mu m) were investigated by magnetization reversal under a combined 20-ns-wide microwave impulse and a 2-ns-wide pulsed field. The switching field was clearly reduced by cooperative switching and was independent of the pulsed field width (for widths between 2 and 10 ns). This result suggests that magnetization assisted by the combined microwave field occurs within 2 ns. (C) 2015 The Japan Society of Applied Physics

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Large anisotropy of Gilbert damping constant in L2(1)-ordered Co2FeSi film

Yuichi Kasatani, Shinya Yamada, Hiroyoshi Itoh, Masanobu Miyao, Kohei Hamaya, Yukio Nozaki

APPLIED PHYSICS EXPRESS （IOP PUBLISHING LTD）  7 （ 12 ） 123001 (4 pages) 2014年12月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  1882-0778

　概要を見る

We experimentally demonstrated anisotropic damping of the magnetization dynamics in a highly ordered Heusler compound Co3-xFexSi (x = 1.0, 2.0, and 3.0). The field-swept ferromagnetic resonance linewidth as a function of the resonant frequency was measured to exclude extrinsic contributions from two-magnon scattering and inhomogeneous line-broadening. In L2(1)-ordered Co2FeSi film, a wide variation in the intrinsic Gilbert damping constant from 0.0023 to 0.0061 was clearly observed in the (111) plane, where a weak uniaxial magnetic anisotropy was formed via low-temperature epitaxial growth. The large anisotropy of the Gilbert damping constant was suppressed by increasing x, which suppresses the half-metallicity in Co3-xFexSi films. (C) 2014 The Japan Society of Applied Physics.

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Large anisotropy of Gilbert damping constant in L21-ordered Co2FeSi flms.

Y. Kasatani, S. Yamada, H. Itoh, M. Miyao, K. Hamaya, and Y. Nozaki

Applied Physics Express （The Japan Society of Applied Physics）  7   123001 (4 pages) 2014年11月

研究論文（学術雑誌）, 共著, 査読有り

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Coupled oscillations of vortex cores confined in a ferromagnetic elliptical disk

H. Hata, M. Goto, A. Yamaguchi, T. Sato, Y. Nakatani, and Yukio Nozaki

Physical Review B （American Physical Society）  90 （ 9 ） 104418 (14 pages) 2014年09月

研究論文（学術雑誌）, 共著, 査読有り

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表面弾性波を用いた磁化ダイナミクスの励起とその電気的検出

柳澤翔吾, 能崎 幸雄

電気学会研究会資料 （電気学会）  MAG-14-113   1-6 2014年08月

研究論文（その他学術会議資料等）, 共著

Microwave-Assisted Magnetization Reversal of Exchange-Coupled Composite Nanopillar With Large Gilbert Damping Constant

T. Tanaka, S. Kashiwagi, Y. Otsuka, Y. Nozaki, Y. Hong, and K. Matsuyama

IEEE Transactions on Magnetism （IEEE）  50 （ 1 ） 300503 (4 pages) 2014年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0018-9464

　概要を見る

Microwave-assisted magnetization reversal (MAMR) characteristics of a single-exchange-coupled composite nanopillar, which consists of ferromagnetically coupled soft and hard magnetic sections, have been discussed in terms of Gilbert damping constant using micromagnetic simulation. The results indicate the occurrence of significant MAMR even when the damping constant of the hard magnetic section is large. The results obtained in this paper greatly contrast those obtained with single-phase hard magnetic pillars. We also found that the magnetization switching time tends to be shorter when the damping constant of the hard magnetic section is large.

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次世代磁気記録へのマイクロ波技術の応用

能崎 幸雄

電気学会研究会資料 （電気学会）  MAG-13-155~173   55-60 2013年12月

研究論文（その他学術会議資料等）, 単著

Characteristic field angular dependence of magnetization switching assisted by spin wave excitation

Takeshi Seki, K. Hotta, H. Imamura, Yukio Nozaki, and Koki Takanashi

Applied Physics Letters （American Institute of Physics）  103 （ 12 ） 122403 (4 pages) 2013年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0003-6951

　概要を見る

We found the characteristic dependence of magnetization switching assisted by spin wave excitation on the magnetic field angle (theta) for exchange-coupled L1(0)-FePt/Permalloy bilayers, where theta was the angle from the easy magnetization axis of L1(0)-FePt. Without the spin wave being excited, an incoherent switching occurred through the domain wall motion. The frequency for the switching field (H-sw) reduction under the spin wave excitation did not depend on theta. This characteristic dependence is attributable to less variation in the resonance frequencies of the spin waves against h. We also increased the efficiency of the H-sw reduction further with theta. (C) 2013 AIP Publishing LLC.

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Frequency dependence of critical switching asteroid of CoCrPt-SiO2 granular film under 50-ns microwave impulse

Naoko Ishida, Yoshikazu Soeno, Koji Sekiguchi, and Yukio Nozaki

Journal of Applied Physics （American Institute of Physics）  114 （ 14 ） 043915 (5 pages) 2013年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Understanding the dynamic process of microwave-assisted magnetization reversal (MAMR) in a dipole-dipole coupled granular perpendicular medium is essential for its application to future magnetic storage devices. We experimentally investigated the magnetization reversal process in CoCrPt-SiO2 granular films in terms of the dependence of the switching field on the strength of an applied in-plane radio-frequency magnetic field. The reversal process changed from non-uniform rotation to uniform rotation when the frequency increased toward the ferromagnetic resonance frequency. In the resonant condition, the switching field agreed well with a model assuming uniform rotation of the magnetization in each grain. The agreement suggests that the decoherence of ferromagnetic resonance due to a dynamic dipolar field is weak in adequately exchange-coupled granular films with a saturation magnetization of 415 emu/cm(3). This finding is significant for the development of the practical medium necessary for MAMR writing. (C) 2013 AIP Publishing LLC.

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マイクロ波磁場による垂直媒体の保磁力低減効果

能崎 幸雄, 石田 尚子, 添野 佳一, 関口 康爾

IEICE Technical Report （電子情報通信学会）  MR2013-6 （ 127 ） 1-6 - 6 2013年07月

研究論文（その他学術会議資料等）, 共著,  ISSN  0913-5685

Electrical Demonstration of Spin Wave Logic Operation.

SATO Nana, SEKIGUCHI koji, NOZAKI Yukio

Applied Physics Express （The Japan Society of Applied Physics）  6   063001 2013年05月

研究論文（学術雑誌）, 共著, 査読有り

Excitation of Continuous Magnetostatic Surface Spin Wave in Ferromagnetic Thin Films.

SATO Nana, SEKIGUCHI koji, NOZAKI Yukio

Journal of the Magnetics Society of Japan （The Magnetics Society of Japan）  37 （ 3-2 ） 214-217 - 217 2013年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-2924

Spin Wave Assisted Reduction in Switching Field of Highly Coercive Iron-Platinum Magnets.

Takeshi Seki, K. Utsunomiya, Yukio Nozaki, H. Imamura, and Koki Takanashi

Nature Communications （Nature Publishing Group）  4   ncomms2737 (6 pages) 2013年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2041-1723

　概要を見る

Recent rapid progress in spintronic and magnetic storage nanodevices has required nano-magnets to balance competing goals for high coercive field and low switching field. However, a decisive route for highly efficient magnetization switching has not been established yet. Here we propose a novel switching method using a spin wave of magnetic structures twisted in a nanometre scale. We have experimentally demonstrated extremely low field-magnetization switching in a highly coercive FePt by using a spin wave excited in a soft magnetic permalloy (Ni81Fe19), where permalloy is exchange-coupled to FePt through the interface. We can tune the switching field by varying the magnitude and frequency of the radio frequency magnetic field, and a significant decrease in switching field by one order of magnitude is achieved under the optimum conditions. The spin wave-assisted magnetization switching is a promising technique for ultralow-energy magnetization manipulation.

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Selective Magnetization Switching with Microwave Assistance for Three-Dimensional Magnetic Recording.

Terumitsu Tanaka, Y. Otsuka, Y. Furomoto,K. Matsuyama, and Yukio Nozaki

Journal of Applied Physics （American Institute of Physics）  113 （ 14 ） 143908 (6 pages) 2013年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

The possibility of selective magnetization switching in a three-layered stacked magnetic pillar was discussed using micromagnetic simulation that considers three-dimensional magnetic recording. Selective magnetization switching is possible with the assistance of a circularly polarized microwave field with an adequate corresponding frequency. This study demonstrates that the value of the saturation magnetization of the magnetic layers is critical in suppressing selective magnetization switching errors caused by magnetostatic fields. A relatively large saturation magnetization of up to 600 emu/cm(3) in the second layer also allows successful selective magnetization switching, thus enabling three-dimensional magnetic recording. However, damping constants smaller than 0.1 for the magnetic layers are crucial in the model calculations because of the limited strength of the microwave fields applied to the stacked magnetic pillar. The leakage flux is also estimated considering a multi-bit reproducing process, where eight-digit signals are obtained depending on the magnetization states of the stacked magnetic pillar. (C) 2013 AIP Publishing LLC [http://dx.doi.org/10.1063/1.4801888]

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Spin torques due to diffusive spin current in magnetic texture.

Kazuhiro Hosono, Junya Shibata, Hiroshi Kohno, and Yukio Nozaki

Physical Review B （American Physical Society）  87 （ 9 ） 094404 (8 pages) 2013年03月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1098-0121

　概要を見る

We present a microscopic theory of spin torque due to diffusive spin currents induced by spin accumulation. The obtained expression is a natural extension of the existing one due to "local" spin currents associated with ordinary electric currents, and is the reciprocal of the spin motive force which induces charge accumulation as studied recently [J. Shibata and H. Kohno, Phys. Rev. B 84, 184408 (2011)]. The result is applied to a domain wall motion in a nonlocal spin injection system, and the torque and force due to diffusive spin current are evaluated. DOI: 10.1103/PhysRevB.87.094404

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高出力マイクロ波による強磁性共鳴を利用したCoCrPtグラニュラー膜の磁化反転

能崎 幸雄, 石田 尚子, 添野 佳一, 小林 尚史, 関口 康爾

日本磁気学会研究会資料 （日本磁気学会）  188   11-14 - 14 2013年01月

研究論文（その他学術会議資料等）, 共著,  ISSN  1882-2940

Micromagnetic Study of Microwave-Assisted Magnetization Reversals of Exchange-Coupled Composite Nanopillars.

Terumitsu Tanaka, Naoyuki Narita, Ayumi Kato, Yukio Nozaki, Yang-Ki Hong, and Kimihide Matsuyama

IEEE Transactions on Magnetism （IEEE）  49 （ 1 ） 562-566 - 566 2013年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0018-9464

　概要を見る

Microwave-assisted magnetization reversals of exchange-coupled composite nanopillars were studied by micromagnetic simulation. Magnetization reversal occurred in one or two frequency regions associated with magnetic resonance arising from the soft magnetic section. Significant reductions in ac field strength and frequency, which are required for magnetization switching, were obtained in cases where there was a large interface exchange constant between the soft and hard sections. It was also found that the large saturation magnetization of the soft magnetic section tends to enhance magnetization switching.

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スピントルク発振素子を用いた再生ヘッドによる多層記録媒体の選択的信号検出

大塚 勇人, 柏木 翔太, 大槻 一紗雄, 田中 輝光, 松山 公秀, 能崎 幸雄

電気関係学会九州支部連合大会講演論文集 （電気・情報関係学会九州支部連合大会委員会）  2013   112 - 112 2013年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

面密度1Tbpsi超の記録が可能な次世代HDD実現のための新技術としてマイクロ波アシスト磁気記録(MAMR)が期待されている．MAMRをビットパターンドメディア(BPM)に適用し，BPMの各磁性ピラーを磁気特性の異なる層で多層構造化して，MAMRの周波数選択性を利用することで，任意の層を選択的に磁化反転させる3次元磁気記録が可能になると考えられる．しかし，従来の方法で各磁性層の漏洩磁界を選択的に検出することは困難であると考えられる．そこで本研究では，スピントルク発振素子（STO）を用いた再生ヘッド(STO再生ヘッド)を用いることで，各磁性層の磁化の向きをSTOの周波数の変化として検出可能であるかを計算機解析により検証した．

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Progress in time-resolved photoemission electron microscopy (PEEM) at BL25SU, SPring-8 -Ac field excitation of magnetic vortex core gyration-

Takuo Ohkochi, Akinobu Yamaguchi, Masato Kotsugi, Hiroshi Hata, Minori Goto, Yukio Nozaki, Tetsuya Nakamura, Hitoshi Osawa, Toyohiko Kinoshita

Japanese Journal of Applied Physics （The Japan Society of Applied Physics）  51   128001 (2 pages) 2012年11月

研究論文（学術雑誌）, 共著, 査読有り

マイクロ波アシスト磁化反転の周波数選択性を利用した多値記録に関する基礎検討

大塚勇人, 風呂本至時, 田中輝光, 松山公秀, 能崎幸雄

信学技報 （電子情報通信学会）  112 （ 294 ） 11-16 - 16 2012年11月

研究論文（研究会，シンポジウム資料等）, 共著,  ISSN  0913-5685

　概要を見る

本研究では,磁気特性の異なる3種の磁性層から成る単一の磁性ピラーを想定し,このピラーに対しマイクロ波アシスト磁化反転特性の周波数選択性を利用することにより,各層の磁化を選択的に反転させる可能性についてマイクロマグネティックシミュレーションにより検証した.その結果,選択的磁化反転を行うためには,各層の飽和磁化の値を小さくし,静磁気的相互作用磁界を抑制することが重要であることがわかった.さらに,本研究で用いたモデルでは,各層のダンピング定数が0.1程度以下となる場合において良好な選択的磁化反転が可能となる結果を得た.

Calculation of Nonlocal Spin Transfer Torque

Kazuhiro Hosono, Junya Shibata, Hiroshi Kohno, Yukio Nozaki

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  48 （ 11 ） 4367 - 4370 2012年11月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

We microscopically derive the spin-transfer torque due to diffusive spin current arising from nonequilibrium spin accumulation as realized in systems with nonlocal spin valve structure. Spin relaxation effects in spin transport is taken into account by introducing magnetic impurities.

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Room temperature microwave-assisted recording on 500-Gbpsi-class perpendicular medium.

Yukio Nozaki, Naoko Ishida, Yoshikazu Soeno, and Koji Sekiguchi

Journal of Applied Physics （American Institute of Physics）  112 （ 8 ） 083912 (7 pages) 2012年10月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Microwave-assisted recording on a 500-Gbpsi-class perpendicular medium was experimentally demonstrated at room temperature. Magnetization reversal under a radio-frequency magnetic field was measured by an electrically shorted coplanar waveguide, which enabled us to evaluate the change in the medium's ferromagnetic resonance spectrum. A frequency-dependent reduction in the switching field was clearly observed in response to a microwave impulse 50 ns in duration. A significant reduction of up to 30% in the coercive field was achieved by applying a microwave impulse with an amplitude of 25 dBm and a frequency of 15 GHz. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759169]

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強磁性薄膜パターンに閉じ込められた磁気渦対の共振スペクトルを用いたスピンダンピング機構の解析

能崎 幸雄, 畑 拓史, 児玉 基, 後藤 穣, 山口 明啓

日本磁気学会研究会資料 （日本磁気学会）  183   31-36 - 36 2012年03月

研究論文（その他学術会議資料等）, 共著,  ISSN  1882-2940

Ferromagnetic resonance properties of granular Co-Cr-Pt films measured by micro-fabricated coplanar waveguides

Takafumi Kobayashi, Naoko Ishida, Koji Sekiguchi, and, Yukio Nozaki

Journal of Applied Physics （American Institute of Physics）  111 （ 7 ） 07B919 (3 pages) 2012年03月

研究論文（学術雑誌）, 共著, 査読有り

マイクロ波整流効果を利用したナノスケール磁性体の磁気ダイナミクスセンシング

山口 明啓, 能崎 幸雄, 福島 章雄，久保田 均，湯浅 新治，宮島 英紀

電気学会全国大会講演論文集 2012 （ 2 ） 2,S2(5)-2,S2(8) 2012年03月

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

高強度マイクロ波インパルスによる垂直媒体保磁力の非線形減少

能崎 幸雄, 石田 尚子, 添野 佳一, 小林 尚史, 関口 康爾

電気学会研究会資料 （電気学会）  MAG-12 （ 169-180 ） 1-6 2011年12月

研究論文（その他学術会議資料等）, 共著

Spin current driven by thermal gradient

Kazuhiro Hosono, Akinobu Yamaguchi, Yukio Nozaki, and Gen Tatara

AIP Conference Proceeding Series （The American Institute of Physics）  1399   731-732 2011年12月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0094-243X

　概要を見る

We consider the spin current induced from temperature gradient in disordered ferromagnet. Using the diagrammatic calculation, we examine a spin current in the longitudinal direction to the temperature gradient.

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マイクロ波整流効果を用いたナノスケール磁性体の磁気ダイナミクス検出

山口 明啓, 後藤 穣, 畑 拓志, 能崎 幸雄

電気学会マグネティックス研究会資料 （電気学会）  MAG-11 （ 52-61 ） 23-28 2011年11月

研究論文（その他学術会議資料等）, 共著

Electric spectroscopy of vortex states and dynamics in magnetic disks

Minori Goto, Hiroshi Hata, Akinobu Yamaguchi,Yoshinobu Nakatani, Takehiro Yamaoka, Yukio Nozaki, and Hideki Miyajiama

Physical Review B （The American Physical Society）  84 （ 6 ） 064406 (9 pages) 2011年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1098-0121

　概要を見る

Spin-polarized radio frequency (RF) currents and RF-Oersted fields resonantly excite a magnetic vortex core confined in a micron-scale soft magnetic disk. In this study, we measured the rectifying voltage spectra caused by the anisotropic magnetoresistance oscillation due to the gyration of the vortex with different polarity and chirality. The measured spectra are presented such that we can determine the vortex properties and strength of the spin torques and Oersted field accurately and directly through analytical calculation.

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Micromagnetic study on microwave-assisted magnetic recording in perpendicular medium with intergrain exchange coupling

Yukio Nozaki, Ayumu Kato, Kenji Noda, Yasushi Kanai, Terumitsu Tanaka, Kimihide Matsuyama Kazuhiro Hosono, Akinobu Yamaguchi, Yukio Nozaki, and Gen Tatara

Journal of Applied Physics （The American Institute of Physics）  109 （ 12 ） 123912 (6 pages) 2011年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

The influence of intergrain exchange coupling on the properties of microwave-assisted magnetization reversal has been investigated. The results of micromagnetic simulation suggest that the microwave frequency realizing the magnetization reversal is increased as the exchange stiffness constant among the magnetic grains becomes larger than 1 x 10(-7) erg/cm if an inhomogeneous magnetization reversal occurred. The numerically expected increase in the microwave frequency was observed experimentally in perpendicularly magnetized Co/Pd multilayer with an exchange stiffness constant of similar to 1 x 10(-6) erg/cm. The simulations of signal recording and reproducing processes in a granular medium with assistance of a microwave field also suggest that an adequate intergrain exchange coupling is required to inhibit the nucleation of small island domains that will suppress the amplitude of the signal-noise ratio of the readback signal. (c) 2011 American Institute of Physics. [doi:10.1063/1.3596805]

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Broadband Ferromagnetic Resonance of Micron-Scale Iron Wires Using Rectifying Effect

Y. Kasatani, A. Yamaguchi, H. Miyajima, Y. Nozaki

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  47 （ 6 ） 1587 - 1590 2011年06月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

The broadband ferromagnetic resonance study on both the single crystalline and polycrystalline Fe wires were performed using the rectifying effect. The effective Gilbert damping in the polycrystalline Fe wire was about three times larger than that in the single crystalline wire. This is attributed to the enhancement of the energy dissipation due to the incoherent rotation of the magnetization at the grains and grain boundaries in the polycrystalline wire. The difference between the experimental data and analytical calculation can be explained by the strong magnetic shape anisotropy that overcomes the external static magnetic field and forces the magnetization to be directed along the wire axis.

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微細磁気構造の制御とデバイス応用

松山 公秀, 田中 輝光, 能崎 幸雄

日本磁気学会研究会資料 （日本磁気学会）  178   23-29 2011年05月

研究論文（その他学術会議資料等）, 共著,  ISSN  1882-2940

Microscopic Theory of diffusive spin current with spin-orbit interaction

Kazuhiro Hosono, Akinobu Yamaguchi, Yukio Nozaki, and Gen Tatara

Physical Review B （The American Physical Society）  83 （ 14 ） 144428 2011年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1098-0121

　概要を見る

We present the diagrammatic calculation of the spin current in the presence of the spin-orbit interaction due to impurity and electromagnetic field. By considering the vertex corrections for the normal impurity and the spin-orbit interaction, we derive both the field-driven and diffusion part of the spin current with side-jump and skew-scattering contributions. We found an alternative source of the spin-density generation, given by del x (A) over dot, where A is an electromagnetic vector potential. This generation mechanism is distinct from the conventional spin accumulation one, given by del . (A) over dot.

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Electrical detection of vortex states in a ferromagnetic disk using the rectifying effect

M. Goto, H. Hata, Yamaguchi, Y. Nakatani, T. Yamaoka, Y. Nozaki

Journal of Applied Physics （The American Institute of Physics）  109 （ 7 ） 07D306 (3 pages) 2011年03月

研究論文（学術雑誌）, 共著, 査読有り

微細加工したコプレーナ線路を用いたマイクロ波アシスト磁化反転実験

能崎 幸雄、上田浩史、小林尚史、田中輝光、松山公秀、山口明啓

信学技報 （電子情報通信学会）  110 （ 438 ） 39-46 2011年03月

研究論文（その他学術会議資料等）, 共著

Time evolution of spin accumulation induced from electric field in ferromagnet

Kazuhiro Hosono, Yukio Nozaki, Akinobu Yamaguchi, Gen Tatara

Journal of Applied Physics （The American Institute of Physics）  109 （ 7 ） 07C901 (3pages) 2011年03月

研究論文（学術雑誌）, 共著, 査読有り

Detection of ferromagnetic resonance in a single-crystalline Fe wire using a rectifying effect

Y. Kasatani, A. Yamaguchi, H. Miyajima, and Y. Nozaki

Journal of Physics （The Institute of Physics）  266 （ 1 ） 012013 (5 pages) 2011年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1742-6588

　概要を見る

The broadband ferromagnetic resonance (FMR) of a single-crystalline Fe microwire was measured using a rectifying effect. The experimental result indicates the uniform mode dominates the system. The effective Gilbert damping factor of the Fe wire was estimated by the rectifying effect. A rectifying spectrum is broadened because of the spin wave excitation and the thermal fluctuation as the input power increases.

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Detection of vortex-core dynamics using current-induced self-bistable rectifying effect

M. Goto, H. Hata, A. Yamaguchi, H. Miyajima, Y. Nakatani, T. Yamaoka, and Y. Nozaki

Journal of Physics （The Institute of Physics）  266 （ 1 ） 012080 (5 pages) 2011年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1742-6588

　概要を見る

A magnetic vortex core confined in a micron-scale magnetic disk is resonantly excited by spin-polarized radio-frequency (rf) current and rf field. We show that rectifying voltage spectra caused by the vortex core resonance is dependent on the core polarity. Rectifying voltage spectra are given by the superposition of the polarity-dependent term and the polarity-independent term. The sign of the polarity-dependent rectifying voltage reverses when the sign of polarity P or external field H is reversed. This experimental result can be explained by the anisotropic magnetoresistance effect caused by the vortex core motion.

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Fourfold in-plane magnetic anisotropy in sputtered (100) MgO/Fe epitaxial films

K. Noda, M. Higuchi, Y. Komaki, T. Tanaka, Y. Nozaki, and K. Matsuyama

Journal of Physics （The Institute of Physics）  266 （ 1 ） 012014 (5 pages) 2011年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1742-6588

　概要を見る

We report structural and magnetic properties of Fe thin films, deposited onto (100)MgO substrates by rf magnetron sputtering. The successful epitaxial growth of Fe&lt;100&gt;(100) parallel to MgO&lt;110&gt;(100) was achieved at a practical growth rate of 0.73 nm/s. The M-H hysteresis measured along Fe&lt;100&gt; directions exhibits a superior squareness with a low coercivity (H-c = 5 Oe). The saturation field along &lt;110&gt; directions, exceeding 500 Oe, demonstrates the crystalline cubic anisotropy comparable to the bulk Fe. The anisotropic properties of the initial susceptibility against an oscillation field of 1 mOe amplitude were also confirmed with inductive measurements.

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微細加工したコプレーナ線路を用いたマイクロ波アシスト磁化反転実験(光記録,一般)

能崎 幸雄, 上田 浩史, 小林 尚史, 田中 輝光, 松山 公秀, 山口 明啓

映像情報メディア学会技術報告 （一般社団法人 映像情報メディア学会）  35   39 - 46 2011年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

1平方インチあたり1テラビットを超える面密度実現が期待されているマイクロ波アシスト記録とは、媒体にマイクロ波磁場を加えることにより強磁性共鳴を誘引し、スピン系のエネルギーを励起することによって磁化反転磁場を低減する方法である。したがって、媒体の強磁性共鳴特性を調べることが本方式の実現に向けて重要である。本稿では、ネットワークアナライザを用いた強磁性薄膜の強磁性共鳴スペクトル測定と、それを応用したマイクロ波アシスト磁化反転検出実験について概説する。

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グラニュラー媒体への狭トラックマイクロ波アシスト磁気記録シミュレーション

加藤 歩，成田直幸，田中輝光，能崎幸雄，金井　靖，松山公秀

信学技報 （電子情報通信学会）  110 （ 310 ） 1-5 - 5 2010年11月

研究論文（その他学術会議資料等）, 共著,  ISSN  0913-5685

　概要を見る

Tbits/inch^2超の面記録密度を有する次世代HDDの実現へ向けた技術の一つとしてマイクロ波帯域の交流磁界を用いたマイクロ波アシスト磁気記録(MAMR)方式が期待されている.本研究ではマイクロマグネティック計算によるMAMRの信号記録・再生シミュレーションを行い,狭記録トラック化について検討した.MAMRでは島状の非反転領域が発生しやすく,それらの減少には,媒体に比較的大きな交換相互作用を導入することが有効であると報告されている.しかし本研究では,比較的大きな交換相互作用の導入は信号対雑音比(SNR)を向上させるものの,同時に記録トラック幅の肥大化を招き,高トラック記録には不向きであることが分かった.また交換相互作用を導入しなくても許容可能なSNRを20dBと仮定すると,本モデルでは1129ktpiという高い記録トラック密度が可能であることが分かった.

Dependence of Magnetization Switching Property with Microwave Assistance on Anisotropy Field for ECC Nano-pillar

N. Narita, T. Tanaka, A. Kato, Y. Nozaki, and K. Matsuyama

Proc. IEEE TENCON2010 （The Institute of Electrical and Electrics Enginnering (IEEE)）     1898-1901 - 1901 2010年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2159-3442

　概要を見る

Magnetic resonance properties for ECC nano-pillar were numerically analyzed. The analysis showed there are three resonance modes in the ECC nano-pillar that ferromagnetic resonances (FMR) at the low and high frequency regions associating with the soft and hard material, and magnetic spin wave resonance at middle frequency region. Microwave assisted magnetization reversals were also simulated assuming ECC nano-pillar with extremely high anisotropy field hard magnetic material. Essential ac field strength and microwave frequency for magnetization reversal were found to be less dependent on anisotropy field for the hard magnetic material, when magnetization reversal is induced by magnetic resonance for the soft magnetic material.

Numerical Study on Inductive Detection of Magnetostatic Spin Wave Packet

Y. Nakashima, K. Nagai, T. Tanaka, K. Matsuyama, and Y. Nozaki

Proc. IEEE TENCON2010 （Institute of Erectrical and Electronics Engineering (IEEE)）     1894-1897 - 1897 2010年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2159-3442

　概要を見る

Fundamental operations in magneto-static spin wave devices of nucleation, propagation and inductive detection for a spin wave packets (magnetic solitons) are numerically studied by using micromagnetic simulations. The collective spin dynamics and device performances are compared for three different spin wave modes. Simulation results of the group velocity reasonably agree with the theoretical prediction under a thin film approximation. Structural and operational parameters are optimized so as to maximize the inductive output voltage V-out. The practical V-out of 0.052 mV/mu m(2) is obtained at optimized parameters in a spin wave mode of magneto-static backward volume wave.

Track density capability of microwave assisted magnetic recording

A. Kato, T. Tanaka, N. Narita, Y. Nozaki, Y. Kanai, Y. K. Hong, K. Matsuyama

55th Annual Conference on Magnetism and Magnetic Materials (MMM), FW-08, Atlanta, GA, U.S.A.    465 2010年11月

筆頭著者, 最終著者, 責任著者, 査読有り

マイクロ波アシスト磁気記録における記録ビットパターンの媒体飽和磁化依存性

田中輝光，加藤　歩，川野敏志，成田直幸，能崎幸雄，金井　靖，松山公秀

電気学会論文誌Ａ （電気学会）  130 （ 7 ） 648-654 - 654 2010年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0385-4205

　概要を見る

Signal recording processes were simulated using micromagnetic calculation for microwave assisted magnetic recording in perpendicular magnetic media. Strong magnetostatic field caused by the large saturation magnetization of the media tends to deteriorate recorded bit patterns resulting in low signal to noise ratio for the play back signal. The moderate exchange interaction fields were shown to improve recording characteristics and increase signal to noise ratio even for the large saturation magnetization media. The influence of thermal fluctuation fields on recording characteristics was also discussed and the influence was negligible for the media assumed in this study.

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マイクロ波アシスト垂直磁気記録における記録トラック幅のオシレーション周波数依存性

加藤歩、成田直幸、野田憲司、田中輝光、能崎幸雄、松山公秀

信学技報 （電子情報通信学会）  109 （ 222 ） 13-18 - 18 2009年10月

研究論文（その他学術会議資料等）, 共著,  ISSN  0913-5685

　概要を見る

Tbits/inch^2を超える超高密度記録を実現するにはエネルギーアシストを併用した信号の記録方式が必要であると予測される.本研究では,エネルギーアシスト記録方式の一つであるマイクロ波アシスト記録方式に着目し,マイクロマグネティックシミュレーションによってスピントルクオシレータを用いたマイクロ波アシスト記録時の磁化挙動を計算し,記録トラック幅とマイクロ波周波数の関係について検討し,マイクロ波周波数が高周波化するにつれて記録トラック幅が広くなることが分かった.また,磁化反転領域がスピントルクオシレータの磁化の回転の向きに依存して,ヘッド主磁極側およびトレーリングリターンヨーク側に遷移することが分かった.

マイクロコプレーナ線路を用いたマイクロ波アシスト記録実験

能崎幸雄、成田直幸、田中輝光、松山公秀

信学技報 （電子情報通信学会）  109 （ 222 ） 1-6 - 6 2009年10月

研究論文（その他学術会議資料等）, 共著,  ISSN  0913-5685

　概要を見る

次世代ハードディスクドライブにおける必須技術と考えられるエネルギーアシスト記録の一つであるマイクロ波アシスト記録の実験的検証を行った。強磁性薄膜上に線幅が1μm以下のマイクロコプレーナ線路を作製し、線路表面に発生するマイクロ波磁界による磁化反転の有無のマイクロ波周波数依存性を詳しく調べた。ネットワークアナライザを用いた磁化反転検出の手法や、マイクロ波アシスト磁化反転特有の臨界スイッチング特性について概説する。

交換結合ナノピラーにおけるマイクロ波アシスト磁化反転挙動の軟磁性層厚依存性

成田直幸、田中輝光、能崎幸雄、松山公秀

信学技報 （電子情報通信学会）  109 （ 222 ） 19-24 2009年10月

研究論文（その他学術会議資料等）, 共著

Microwave-assisted magnetization reversal in a Co/Pd multilayer with perpendicular magnetic anisotropy.

Y. Nozaki, N. Narita, T. Tanaka and K. Matsuyama

Applied Physics Letters （The American Institute of Physics）  95 （ 8 ） 082505 (1-3) 2009年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0003-6951

　概要を見る

Microwave-assisted magnetization reversal in a rectangle of a Co/Pd multilayer with a perpendicular magnetic anisotropy is examined using vector network analyzer ferromagnetic resonance (FMR) spectroscopy. A microwave field is applied along the in-plane direction of the rectangle together with a negative dc easy-axis field smaller than the coercive field. Broadening or splitting of the peak profile in the FMR spectrum suggesting the formation of multidomain structure appears after the microwave field is applied. The dominance of microwave-assisted nucleation of magnetization is supported by the frequency dependence of the probability with which the multidomain structure appears.

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ベクトルネットワークアナライザFMR分光法によるNiFe薄膜パターンのマイクロ波アシスト磁化反転検出

能崎幸雄, 立石健太郎、大田正直、白石壮馬、成田直幸、松山公秀

日本磁気学会第165回研究会論文集 （日本磁気学会）     39 – 44 2009年03月

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

サブミクロン幅NiFe薄膜パターンのマイクロ波アシスト磁化反転

立石健太郎, 白石壮馬, 能崎幸雄, 松山公秀

Journal of Magnetic Society of Japan （The Magnetic Society of Japan）  33 （ 3 ） 208 – 211 2009年03月

研究論文（学術雑誌）, 共著, 査読有り

Material dependence of the thermally assisted magnetization reversal properties in microstructured Co/Pd multilayers.

B. Purnama, T. Tanaka, Y. Nozaki, K. Matsuyama

Applied Physics Express （The Japan Society of Applied Physics）  2 （ 3 ） 033001 (1-3) 2009年02月

研究論文（学術雑誌）, 共著, 査読有り

Numerical study on microwave-assisted magnetization reversal of magnetic particles several tens of nanometers wide with perpendicular anisotropy.

Y. Nozaki, M. Ohta, N. Narita, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  105 （ 7 ） 07B901 (1-3) 2009年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Microwave-assisted magnetization reversal (MAMR) is numerically investigated for perpendicularly magnetized particles with a natural ferromagnetic resonance frequency of 22.5 GHz. The precession angle of magnetization can be enhanced intensively by increasing the amplitude of the ac hard-axis field with an optimum frequency. However, the precession of magnetization about the easy axis becomes unstable as the precession angle reaches a critical value because the easy-axis component of the effective field exerted on the magnetization becomes zero. The analysis of magnetization dynamics in MAMR showed that the precession of magnetization about an in-plane axis, appearing after the easy-axis component of the effective field becomes zero, plays an important role in the irreversible switching of magnetization. © 2009 American Institute of Physics.

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Magnetic properties of epitaxially grown Fe3Si/Ge(111) layers with atomically flat heterointerfaces.

Y. Ando, K. Hamaya, K. Kasahara, K. Ueda, Y. Nozaki, T. Sadoh, Y. Maeda, K. Matsuyama, and M. Miyao

Journal of Applied Physics （The American Institute of Physics）  105 （ 7 ） 07B102 (1-3) 2009年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

We study magnetic properties of epitaxial Fe3 Si layers grown on Ge(111) with atomically flat interfaces. An unexpected uniaxial magnetic anisotropy is observed in the film plane for all as-grown samples, and the direction of the uniaxial easy axis is different for each of these samples. By postgrowth annealing, surprisingly, the random orientation of the uniaxial easy axis is aligned to a direction along about [0 1- 1], together with a reduction in the saturation magnetization. We discuss a possible mechanism of the variation in the magnetic properties after the annealing. © 2009 American Institute of Physics.

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Experiments on microwave-assisted magnetization reversal in a submicron-scale Permalloy single element with a zero-field resonance frequency of 6.3 GHz.

Y. Nozaki, K. Tateishi, S. Taharazako, S. Yoshimura, K. Matsuyama

Applied Physics Express （The Japan Society of Applied Physics）  2 （ 3 ） 033002 (1-3) 2009年02月

研究論文（学術雑誌）, 共著, 査読有り

Bistable control of ferromagnetic resonance frequencies in ferromagnetic trilayered dots.

Y. Nozaki, K. Tateishi, S. Taharazako, S. Yoshimura, and K. Matsuyama

The Journal of Applied Physics （The American Institute of Physics）  105 （ 1 ） 013911 (1-5) 2009年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

The ferromagnetic resonance (FMR) properties of submicron-scale Ni(81)Fe(19)/Cu/Ni(81)Fe(19) trilayered dots were investigated for application in programable microwave absorbers for broadband filter devices. The trilayered dot shows binary FMR frequencies, depending on the relative orientation of magnetization in the top and the bottom magnetic layers. A parallel configuration of magnetization, which exhibits a lower FMR frequency than that for an antiparallel configuration, can be metastable as the lateral aspect ratio of the dot is larger than the threshold value governed by the Cu layer thickness. The difference in the FMR frequencies between the parallel and antiparallel configurations is gradually decreased with elongation of the dot. This is associated with the suppression of the magnetostatic coupling energy that stabilizes the antiparallel configuration. It was also found that the magnetic configurations can be programed by the selective application of easy-and hard-axis magnetic fields used to saturate the magnetization. This is an appropriate manner to realize the antiparallel configuration of magnetization in the case of a dot with a plural stack of magnetic layers with the same coercive field. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3042231]

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Stochastic simulation of thermally assisted magnetization reversal in sub-100 nm dots with perpendicular anisotropy.

B. Purnama, M. Koga, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （The Europian Physical Society）  321 （ 9 ） 1325 – 1330 - 1330 2009年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Thermally assisted magnetization reversal of sub-100 nm dots with perpendicular anisotropy has been investigated using a micromagnetic Langevin model. The performance of the two different reversal modes of (i) a reduced barrier writing scheme and (ii) a Curie point writing scheme are compared. For the reduced barrier writing scheme, the switching field H(swt) decreases with an increase in writing temperature but is still larger than that of the Curie point writing scheme. For the Curie point writing scheme, the required threshold field H(th), evaluated from 50 simulation results, saturates at a value, which is not simply related to the energy barrier height. The value of H(th) increases with a decrease in cooling time owing to the dynamic aspects of the magnetic ordering process. Dependence of H(th) on material parameters and dot sizes has been systematically studied. (C) 2008 Elsevier B.V. All rights reserved.

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マイクロコプレーナ線路を用いたマイクロ波アシスト記録実験(固体メモリおよび一般)

能崎 幸雄, 成田 直幸, 田中 輝光, 松山 公秀

映像情報メディア学会技術報告 （一般社団法人 映像情報メディア学会）  33   1 - 6 2009年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

次世代ハードディスクドライブにおける必須技術と考えられるエネルギーアシスト記録の一つであるマイクロ波アシスト記録の実験的検証を行った。強磁性薄膜上に線幅が1μm以下のマイクロコプレーナ線路を作製し、線路表面に発生するマイクロ波磁界による磁化反転の有無のマイクロ波周波数依存性を詳しく調べた。ネットワークアナライザを用いた磁化反転検出の手法や、マイクロ波アシスト磁化反転特有の臨界スイッチング特性について概説する。

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交換結合ナノピラーにおけるマイクロ波アシスト磁化反転挙動の軟磁性層厚依存性(固体メモリおよび一般)

成田 直幸, 田中 輝光, 能崎 幸雄, 松山 公秀

映像情報メディア学会技術報告 （一般社団法人 映像情報メディア学会）  33   19 - 24 2009年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

マイクロ波アシスト磁気記録媒体として硬磁性体と軟磁性体を積層した構造の交換結合複合媒体に着目し,一本の交換結合ナノピラーのマイクロ波アシスト磁化反転挙動についてマイクロマグネティックシミュレーションを用いて解析した.交換結合ナノピラーでは,軟磁性部の厚みが交換長に比べて十分に短い場合には軟磁性部と硬磁性部の磁化が均一な磁化挙動を示すのに対し,軟磁性部の厚みが交換長と同程度の場合には2つの特有の周波数で,それぞれ硬磁性部および軟磁性部が支配的な磁化挙動を示すことが分かった.また,磁化の反転に必要な交流磁界強度およびマイクロ波周波数は硬磁性体のみ場合と比較して大幅に低減されることが分かった.

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マイクロ波アシスト垂直磁気記録における記録トラック幅のオシレーション周波数依存性(固体メモリおよび一般)

加藤 歩, 成田 直幸, 野田 憲司, 田中 輝光, 能崎 幸雄, 松山 公秀

映像情報メディア学会技術報告 （一般社団法人 映像情報メディア学会）  33   13 - 18 2009年

筆頭著者, 最終著者, 責任著者, 査読有り

　概要を見る

Tbits/inch^2を超える超高密度記録を実現するにはエネルギーアシストを併用した信号の記録方式が必要であると予測される.本研究では,エネルギーアシスト記録方式の一つであるマイクロ波アシスト記録方式に着目し,マイクロマグネティックシミュレーションによってスピントルクオシレータを用いたマイクロ波アシスト記録時の磁化挙動を計算し,記録トラック幅とマイクロ波周波数の関係について検討し,マイクロ波周波数が高周波化するにつれて記録トラック幅が広くなることが分かった.また,磁化反転領域がスピントルクオシレータの磁化の回転の向きに依存して,ヘッド主磁極側およびトレーリングリターンヨーク側に遷移することが分かった.

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Heat-assisted magnetization reversal using pulsed laser irradiation in patterned magnetic thin film with perpendicular anisotropy.

K. Waseda, R. Doi, B. Purnama, S. Yoshimura, Y. Nozaki, and K. Matsuyama

IEEE Transactions on Magnetics （The Institute of Electrical and Electron Enginnering）  44 （ 11 ） 2483 – 2486 - 2486 2008年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0018-9464

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Cooling velocity of patterned Tb-Fe film with a lateral size of 50 x 50 mu m(2) was experimentally investigated for the application to heat-assisted writing operation in high-density magnetic random access memories. The patterned Tb-Fe film was heated-up by using pulsed YAG laser irradiations with the duration of 1 ns which is realizing a semi-adiabatic heating process. The ratio of magnetization reversal in the patterned Tb-Fe film was estimated by measuring an anomalous Hall voltage. The main results are as follows: (1) Magnetic field required for magnetization reversal of Tb-Fe film was decreased from 1.4 kOe to 200 Oe by applying the heat-assisted magnetization reversal method. (2) Cooling velocity of patterned Tb-Fe film can be estimated by using pulsed magnetic fields with various time delays from the pulsed laser irradiation. (3) With increasing the thermal conductivity coefficient of electrical leads, the velocity to cool the patterned Tb-Fe film increased.

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Structural control of magnetic properties in Co/Pd multilayer for heat assisted perpendicular MRAM application.

B. Purnama, K. Waseda, S. Yoshimura, Y. Nozaki, K. Matsuyama

Research Reports on ISEE of Kyushu University （Kyushu University）  13 （ 2 ） 75 – 80 - 79 2008年09月

研究論文（大学，研究機関等紀要）, 共著, 査読有り,  ISSN  1342-3819

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Temperature dependence of magnetic properties in [Co/Pd]_N multilayer have been systematically studied for lithographically patterned samples with different Co thicknesses t_Co and the bilayer number N by extraordinary Hall effect measurements. The perpendicular coercive field H_c, decreases with the increase of t_Co, excepting a very thin thickness of 1 Å. While a threshold temperature (T_th) of H_c, vanishing linearly increases with the increase of t_Co. The H_c, and T_th, monotonously increases with the increase of N, ranged from 5 to 50. The superior crystalline structure for samples with the larger N was confirmed from enhanced Co/Pd(111) peak height in the XRD pattern. A practical thermal activation coefficient α of 174 was evaluated from a sweep rate dependence of H_c. A marked improvements for the heat assisted MRAM application was attained by air annealing of [Co(1.7Å)Pd(8Å)]_30 at 220℃, that is, the H_c was increased from 1.3 kOe to 2.9 kOe, while T_th reduced from 210℃ to 190℃.

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High sensitive detection of susceptibility modulation by LC resonator embedded with ferromagnetic multilayer.

M. Zhang, Y. Nozaki, K. Matsuyama

Research Reports on ISEE of Kyushu University （Kyushu University）  13 （ 2 ） 89 – 93 - 93 2008年09月

研究論文（大学，研究機関等紀要）, 共著, 査読有り,  ISSN  1342-3819

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eng=In the present study, high sensitive detection of the reversible susceptibility modulation in the magnetic thin film was performed by an LC circuit resonant technique. A flat pick-up coil with the inductance of 0.80 μH and a capacitance of 100 pF construct the LC resonant circuit. The reversible susceptibility x of the magnetic thin film, embedded in the pick-up coil, was measured with a sinusoidal exciting field (H). The out put signal was modulated by applying an orthogonal bias field (H_b). A multilayer sample of [NiFe(100 nm)/Cu(10 nm)]_20, exhibits the most sensitive modulation effect among the fabricated samples. That is, the resonant frequency f_r was decreased from 11.58 MHz (H_b = 0 Oe) to 8.22 MHz (H_b = 7 Oe) at H_<ex> = 2.5 mOe, suggesting the marked increase of x . The value of H_b, which minimizes f_r, is comparable to the anisotropy field. Thus, the observed drastic increase of x can be associated with the compensation of the anisotropy with H_b, as confirmed from the theoretical prediction. The practical out put voltage change of 55%/Oe was realized for the fabricated resonator.

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強磁性薄膜パターンのマイクロ波アシスト磁化反転実験

能崎幸雄, 立石健太郎、大田正直、白石壮馬、成田直幸、松山公秀

電気学会マグネティクス研究会論文集 （電気学会）  8   MAG-08-99 (1-8) - 10 2008年08月

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

Simulation of thermally assisted reversal of micro-magnetization in nano-dot with perpendicular magnetization.

M. Koga, B. Purnama, Y. Nozaki, K. Matsuyama

Journal of Magnetic Society of Japan （The Magnetic Society of Japan）  32 （ 4 ） 477 – 482 - 482 2008年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1882-2924

　概要を見る

The thermally assisted reversal of micro-magnetization was simulated for sub-100-nm dots with perpendicular magnetization by using a Langevin-Landau-Lifshitz-Gilbert equation, where thermal effects are modeled by random fields. Two different thermally assisted reversal methods of 1) a thermal relaxation scheme and 2) a switching scheme were compared. Superior performance was obtained for the thermal relaxation scheme from the view point of reducing the reversal field. An auto correlation function in the time domain was introduced to analyze the stochastic properties of the thermally fluctuating directions of magnetization.

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Influence of interlayer magnetostatic coupling on the ferromagnetic resonance properties of lithographically patterned ferromagnetic trilayers.

Y. Nozaki, K. Tateishi, S. Taharazako, S. Yoshimura, and K. Matsuyama

Applied Physics Letters （The American Institute of Physics）  92 （ 16 ） 161903 (1-3) 2008年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0003-6951

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The influence of magnetostatic coupling in a Ni(81)Fe(19)/Cu/Ni(81)Fe(19) elliptical element on the ferromagnetic resonance (FMR) properties was experimentally and numerically investigated. Discontinuous variations in the FMR frequencies were observed when the relative orientation of magnetization was switched between parallel and antiparallel. Furthermore, the trilayer element exhibits field-insensitive FMR properties for magnetization of antiparallel orientation. This is attributable to the conflicted magnetic field dependence of the FMR frequency in the top and bottom Ni(81)Fe(19) layers with antiparallel magnetization. (c) 2008 American Institute of Physics.

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Crystalline structure and magnetic properties of Fe2CrSi Heusler alloy films: New ferromagnetic material for high-performance magnetic random access memory

S. Yoshimura, H. Asano, Y. Nakamura, K. Yamaji, Y. Takeda, M. Matsui, S. Ishida, Y. Nozaki, K. Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  103 （ 7 ） 07D716 (1-3) 2008年04月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

A new Heusler alloy, Fe2CrSi, which has high spin polarization (P), low saturation magnetization (M-s), and a low Curie temperature (T-C), was investigated in order to fabricate high-performance magnetic tunnel junctions (MTJs) with a high tunnel magnetoresistance ratio and with low critical current for the spin-transfer switching method, or a low switching field for the thermally assisted magnetization reversal technique. The main results are as follows: (1) P and the magnetic moment of Fe2CrSi with an L2(1) structure were 0.98 and 1.98 mu(B)/f.u., respectively, according to density of states calculations. (2) Fe2CrSi films show the (100) orientation with a B2 structure on a MgO substrate upon a thermal treatment with optimum temperature and duration. (3) Fe2CrSi films have M-s and T-C values of 385 emu/cm(3) and 630 K, respectively. (4) The (100) oriented epitaxial MTJs are produced with Fe2CrSi films fabricated with the optimized thermal treatment condition. It is found that the Fe2CrSi Heusler alloy films are a suitable ferromagnetic material for high-performance magnetic random access memory. (C) 2008 American Institute of Physics.

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Crystalline structure and magnetic property of Fe2CrSi Heusler alloy films - New ferromagnetic material for high performance MRAM -.

S. Yoshimura, H. Asano, Y. Nakamura, K. Yamaji, Y. Takeda, M. Matsui, S. Ishida, Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  103 （ 7 ） 07D716 (1-3) 2008年

研究論文（学術雑誌）, 共著, 査読有り

Micromagnetic simulation of thermally assisted magnetization reversal in magnetic nano dot with perpendicular anisotropy.

B. Purnama, Y. Nozaki, K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  310   2683 – 2685 2007年11月

研究論文（学術雑誌）, 共著, 査読有り

High sensitive detection of field induced susceptibility modulation with circuit resonance.

M. Zhang, K. Shimizu, Y. Nozaki, K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  310   2746 – 2748 2007年11月

研究論文（学術雑誌）, 共著, 査読有り

Microwave-assisted magnetization reversal in 0.36-micrometer-wide Permalloy wires.

Y. Nozaki, K. Tateishi, S. Taharazako, M. Ohta, S. Yoshimura, and K. Matsuyama

Applied Physics Letters （The American Institute of Physics）  91 （ 12 ） 122505 (1-3) 2007年09月

研究論文（学術雑誌）, 共著, 査読有り

Microwave-assisted magnetization reversal in 0.36-mu m-wide Permalloy wires

Y. Nozaki, K. Tateishi, S. Taharazako, M. Ohta, S. Yoshimura, K. Matsuyama

APPLIED PHYSICS LETTERS （AMER INST PHYSICS）  91 （ 12 ） 122505 (1-3) 2007年09月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0003-6951

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Microwave-assisted magnetization reversal in a 0.36 mu m wide Ni80Fe20 wire with a natural ferromagnetic resonance frequency of 8.42 GHz was investigated experimentally. Magnetization switching could be detected from a discontinuous change in the ferromagnetic resonance frequency of the wire. The application of microwaves with a frequency of 7.5 GHz and a power of 19.2 dBm reduced the switching field from 217 to 142 Oe. While high-power microwave-assisted switching reduced the dc switching field, it substantially broadened the switching field distribution. This is mainly attributed to inhomogeneous resonance properties of the nucleation sites in the wire. (c) 2007 American Institute of Physics.

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A magnetic force microscopy study of microwave-assisted magnetization reversal in submicron-scale ferromagnetic particles.

Y. Nozaki, M. Ohta, S. Taharazako, K. Tateishi, S. Yoshimura, and K. Matsuyama

Applied Physics Letters （The American Institute of Physics）  91 （ 8 ） 082510 (1-3) 2007年08月

研究論文（学術雑誌）, 共著, 査読有り

Magnetic force microscopy study of microwave-assisted magnetization reversal in submicron-scale ferromagnetic particles

Y. Nozaki, M. Ohta, S. Taharazako, K. Tateishi, S. Yoshimura, K. Matsuyama

APPLIED PHYSICS LETTERS （AMER INST PHYSICS）  91 （ 8 ） 082510 (1-3) 2007年08月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0003-6951

　概要を見る

Changes in magnetic-domain configurations caused by the application of radio-frequency (rf) fields ranging from 3 to 18 GHz were observed using magnetic force microscope. rf fields barely altered the magnetization of Co particles with scattered large crystalline anisotropy; however, for NiFe particles, magnetization switching occurred when the rf approached the natural ferromagnetic-resonance frequency of 5.92 GHz. However, the reduction of the switching field fluctuated widely among the particles. Scattering of the effective energy barrier to thermal fluctuations caused by an applied rf field can explain the stochastic switching properties.

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微細加工領域での磁性物理

松山公秀, 能崎幸雄

Journal of Magnetic Society of Japan （The Magnetic Society of Japan）  2 （ 7 ） 352 – 357 - 357 2007年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  1880-7208

Numerical analysis of thermally assisted magnetization reversal in rectangular MRAM cells consisted of exchange coupled bilayer.

Y. Nozaki, Y. Isowaki, A. Hashimoto, B. Purnama, K. Matsuyama

Journal of Magnetics Society of Japan （The Magnetic Society of Japan）  30 （ 6-2 ） 574 – 577 - 577 2006年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0285-0192

　概要を見る

Time evolution of magnetization during a cooling process in thermally assisted magnetization reversal of rectangular MRAM cell has been numerically investigated by taking account of not only temperature variations of material parameters but also a thermal fluctuation effect. The rectangular MRAM cell with 100×150×20 nm³ in size is assumed, where the shape anisotropy dominates the switching property. The threshold amplitude of magnetic field required for a successful thermally assisted switching is decreased as the exchange stiffness constant is changed from 1×10^-6 to 1×10^-7 erg/cm. The time for the magnetization to relax into the bias field direction can be reduced by increasing the bias field amplitude. To switch the magnetization within 1 ns, it is found that the bias field should be larger than 165 Oe. An exchange coupling field in a ferromagnetic bilayer system is considered to be available for producing such a large bias field required for a faster switching in thermally assisted MRAMs.

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Numerical study for ballistic switching of magnetization in single domain particle triggered by a ferromagnetic resonance within a relaxation time limit.

Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  100 （ 5 ） 053911 (1-5) 2006年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

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Magnetization reversal via successive ballistic rotation caused by an application of alternative field temporally varying within a relaxation time limit has been numerically investigated. As the Gilbert damping constant is smaller than 0.03, a pronounced beat appears in the temporal evolution of rotating angle of magnetization. The amplitude of the rotating angle at the first peak of the beat is larger than that achieved in the stable ferromagnetic resonance, so that the magnetization reversal occurred at the first peak of the beat. Consequently, subnanosecond switching of magnetization is realized even though a ferromagnetic resonant phenomenon is utilized to enhance the rotating angle of magnetization. In such a switching scheme, it is most important to optimize the frequency of the alternating field to ensure a practical margin of the operation current creating the switching field. (c) 2006 American Institute of Physics.

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Numerical analysis of successive ballistic rotation of magnetization caused by an application of sinusoidal magnetic fields.

Y. Nozaki, K. Matsuyama

Japanese Journal of Applied Physics （The Japan Society of Applied Physics）  45 （ 29-32 ） L758 – L760 2006年07月

研究論文（学術雑誌）, 共著, 査読有り

Reconfigurable ferromagnetic resonance properties in nanostructured multilayers.

M. Zhang, Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  99 （ 8 ） 08G307(1-3) 2006年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

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Ferromagnetic resonance properties in nanostructured multilayers are numerically investigated for the application of spintronics devices. The resonance frequency can be shifted by switching the magnetization state between a parallel and an antiparallel configuration. These remanent states are selectively initialized by choosing the saturation direction of magnetization. In this paper, the signal independency between the two resonant states, the amplitude of the magnetization rotation at the resonance frequency, and the response time to reach equilibrium resonance are systematically studied as a function of the geometrical and magnetic parameters. (C) 2006 American Institute of Physics.

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Numerical study for successive ballistic motion of magnetization in single domain particle caused by alternating magnetic fields

Y. Nozaki, K. Matsuyama

INTERMAG 2006 - IEEE International Magnetics Conference    923 2006年

筆頭著者, 最終著者, 責任著者, 査読有り

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Thickness dependence of interlayer fringe field coupling in sub micron NiFe/Cu multilayered pillars.

M. Zhang, Y. Nozaki, and K. Matsuyama

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  41 （ 10 ） 2583 – 2585 - 1744 2005年10月

研究論文（学術雑誌）, 共著, 査読有り

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Thickness dependence of interlayer fringe-field coupling in submicrometer NiFe/Cu multilayered pillars

M Zhang, Y Nozaki, K Matsuyama

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  41 （ 10 ） 2583 - 2585 2005年10月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

The effect of fringe-field coupling on the magnetization reversal process in submicrometer scale giant magnetoresistive pillars consisting of [NiFe/Cu](6) has been investigated by means of current perpendicular to plane magnetoresistance measurements and numerical simulations. The parabolic and reversible magnetoresistance curves due to an opposite rotation of magnetization in neighboring NiFe layers were observed. To explain the field sensitivity of the pillars quantitatively, we have proposed a modified single-domain model, where the magnetic energy of the system is reconstructed using the result of the micromagnetic simulation of a magnetostatically coupled bilayer system. The calculated magnetoresistance curves are consistent with the experimental ones. From the calculated results, the amplitude of the saturation field is found to be proportional to the thickness of the ferromagnetic layer and inversely proportional to the square root of the nonmagnetic layer thickness.

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Numerical simulation of write-operation in MRAM memory cell array with magnetostatic interaction

Y. Nozaki, S. Nagayasu, S. Ishii, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  97 （ 10 ） 10P505 (1-3) 2005年05月

研究論文（学術雑誌）, 共著, 査読有り

CPP transport properties of polycrystalline Fe3O4 thin films sputtered on Cu underlayers

F. Qin, Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  97 （ 10 ） 10C315 (1-3) 2005年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Transport properties of sputtered Fe3O4 thin films have been studied with the current perpendicular to plane (CPP) configuration. Fabricated polycrystalline Fe3O4 films exhibit superior CPP conductivity of 12 k Omega(-1) center dot m(-1). In addition to the Verwey transition (VT), observed at 114 K, another type of drastic conductivity change [field induced transition (FT)] was observed at lower temperature (T &lt; 70 K) and higher bias voltage (V-b &gt; 0.18 V) regime. The conductivity change at FT is discontinuous and several orders in magnitude. The transition temperature for FT presents considerable Vb dependence, contrarily no distinguished dependence for VT. (c) 2005 American Institute of Physics.

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Numerical simulation of write-operation in a magnetic random access memory cell array with a magnetostatic interaction

Y Nozaki, H Terada, K Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  97 （ 10 ） 10P505 (1-3) 2005年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

The margin for selective write-operation in a current coincident scheme has been numerically evaluated by considering a magnetostatic interaction in a magnetic random access memory cell array. For a conventional method, the margin over 20% cannot be achieved as the cell size is smaller than 0.2 x 0.4 mu m(2). This is mainly attributed to the degradation of field localization created by a conductor current. The minimum cell size ensuring the practical margin can be decreased to 0.16 x 0.24 mu m(2) by using an opposing current flowing through neighboring conductors. The margin is found to be remarkably decreased as a current pulse width becomes less than 0.4 ns because of a gyromagnetic effect. (c) 2005 American Institute of Physics.

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Fabrication and characterization of ferromagnetic tunnel junction with transition metal oxides.

F. Qin, Y. Nozaki, K. Matsuyama

Research Reports on ISEE of Kyushu University （Kyushu University）  10 （ 2 ） 63 – 66 - 66 2005年03月

研究論文（大学，研究機関等紀要）, 共著, 査読有り,  ISSN  1342-3819

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A novel ferromagnetic tunnel junction with transition metal oxides has been fabricated with photo-lithographic technique. Well defined tunneling properties were observed in a novel barrier material of TiO_x with the thickness down to 2 nm. Spin dependent transport properties have been confirmed for Fe_3O_4/ TiO_x/M (M =Co, Co/NiFe, NiFe) tunnel junctions, where highest magneto-resistance (MR) change of 7% was observed for Co. Drastic improvement of field sensitivity was attained with the exchange coupled Co/NiFe bi-layer.

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Electrically induced conductivity switching in sputtered Fe3O4 thin film.

F. Qin, Y. Nozaki, K. Matsuyama

Research Reports on ISEE of Kyushu University （Kyushu University）  9 （ 2 ） 85 – 88 - 88 2004年09月

研究論文（大学，研究機関等紀要）, 共著, 査読有り,  ISSN  1342-3819

　概要を見る

Electric transport properties have been studied for Fe_3O_4 thin films with current perpendicular to plane geometry, aiming at development of oxide spintronics devices. Excellent conductivity comparable to a bulk single crystal was attained by optimizing an under layer material and film deposition condition. A novel conductivity switching, up to three orders of magnitude, was observed. The threshold value of electric field for switching and its temperature dependence were investigated.

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Effect of metallic under-layer on structural and magnetic properties of sputtered Fe3O4 films

F. Qin, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   e1835 – e1837 - E1837 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

High-quality Fe3O4 films are fabricated on glass substrates with metallic underlayers of Cr/Cu or Al by RF magnetron sputtering at relatively low deposition temperature of 300 degrees C. The measured values of saturation magnetization M-s are 462 emu/cm(3) for Al(50 nm)/ Fe3O4(200 nm) and 422 emu/cm(3) for Cr(45 nm)/ Cu(300 nm)/ Fe3O4(200 nm), which are drastically enhanced compared with that for the reference sample deposited directly on a glass substrate, and practically comparable to the bulk value of 477 emu/ cm(3). (C) 2003 Elsevier B. V. All rights reserved.

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Controlling of spin orientation in a pseudo spin valve MRAM cell with pulsed conductor currents

J. Kikuchi, A. Akiyoshi, H. Terada, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   1895 – 1897 - 1897 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

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Reversal of spin orientation using current-carrying conductors are studied for a micro-structured pseudo-spin valve material of Co79Fe21(3 nm)/Cu(4 nm)/Co73Fe27(4 nm) by magnetoresistive measurements. Selective spin reorientation in one of the two magnetic layers are successfully performed with practical current amplitude smaller than 10 mA/mum. Compositionally differentiated coercive field in the CoFe films would be a dominant cause for the selectivity of the spin reorientation. (C) 2004 Elsevier B.V. All rights reserved.

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Thermal stability of Co90Pt10 islands with relief-structured samples

Y. Nozaki, S. Nagayasu, S. Ishii, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   e1319 – e1321 - E1321 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Thermal stability of submicron scale Co90Pt10 island has been investigated using relief-structured giant magnetoresistive samples. Elongated islands with the lateral dimension of 0.5 mu m x 2.0 mu m and the thickness of 6 nm show nonlinear increase of the coercive field with decreasing temperature. The evaluated energy barrier becomes larger than 80k(B)T for the thickness ranging from 6 to 18 nm. (C) 2003 Elsevier B.V. All rights reserved.

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Effect of magnetostatic fringe field coupling on magnetic properties of nano-structured single domain particle arrays

32. H. Oishi, S. Ishii, Y. Nozaki, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  272-276   e1355 – e1357 - E1357 2004年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

We have numerically investigated the co-operative magnetization reversal of magnetic particle arrays with fringe fields coupling. Demagnetization processes of one-dimensional particle arrays are studied taking the inter-particle separation S and uniaxial anisotropy K-u as parameters. Particles are found to rotate toward same or opposite directions depending on the values of S and K-u: (C) 2003 Elsevier B.V. All rights reserved.

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Magnetic and electric properties of Fe3O4 thin films sputtered on metallic underlayer

F. Qin, Y. Nozaki, and K. Matsuyama

IEICE Transactions on Electronics （The Institute of Electronics, Information and Communication Engineers）  E87-C （ 2 ） 189 – 192 - 192 2004年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0916-8524

　概要を見る

High-quality Fe3O4 thin films have been fabricated onto metallic underlayers of Cr/Cu and Al by rf-magnetron sputtering at low substrate temperatures (&lt; 573 K). The measured saturation magnetizations M-s are 462 emu/cm(3) for Al (50 nm)/Fe3O4 (200 nm) and 422 emu/cm(3) for Cr (45nm)/Cu (300nm)/Fe3O4 (200nm), which are markedly enhanced compared with that for the reference sample deposited directly on a glass substrate, and practically comparable to the bulk value of 477 emu/cm(3). Highly conductive transport with an order-disorder change of the Verwey transition was observed in the current-perpendicular-to-plane geometry. The order of decrease in coercive field was achieved by exchange coupling with an overlaid NiFe layer.

Non-linear temperature dependence of switching fields in relief-structured Co/Ni80Fe20 particles

Y. Nozaki, K. Matsuyama, and S. Ishii

Journal of Applied Physics （The American Institute of Physics）  93 （ 11 ） 9182 – 9185 - 9185 2003年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

The temperature dependence of the switching properties in low sub-mum scale Co/Ni80Fe20 particles with different aspect ratios L/w (= 1-6, w = 0.4 mum) and thicknesses t (= 1-5 nm) are investigated using magnetotransport measurements of relief structured. films with giant magnetoresistance. The shape of each particle is a parallelogram with slope angle theta(=0degrees-60degrees). The switching field of the particles increased with theta due to the variation of the end-domain configuration. Nonlinear temperature dependence of the switching field was observed, which could be explained by the thermal nucleation theory of the magnetization reversal at below 150 K. The amplitude of the energy barrier height DeltaE for the reversal was strongly suppressed by decreasing the thickness of the particles. This degradation of the thermal stability may be caused by the variation of the film morphology by decreasing the thickness. (C) 2003 American Institute of Physics.

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Switching behavior of cross contacting current perpendicular to plane giant magnetoresistance structure fabricated by two-step ion milling technique

H Oishi, Y Nozaki, K Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  93 （ 10 ） 7613 - 7615 2003年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

A current perpendicular to plane giant magnetoresistance structure with a cross contact geometry was fabricated by a two-step ion-milling technique. Multilayer pillars with various layer structures and a lateral dimension down to 0.4 mum were embedded between orthogonal top and bottom electrodes. The microfabricated cross point structure minimizes the influence of electrode resistance in measurements of magnetoresistance in current perpendicular to plane geometry. Individual switching of Co layer was observed in a pillar with layer structure of [Co(10 nm)/Cu(4 nm)/Co(2 nm)/Cu(10 nm)](3) and lateral dimension of 0.4x2.0 mum(2). Distinct three-step resistance change was observed for the rising part of the magnetoresistance (MR) curve, corresponding to the switching of Co(2 nm) layers. Somewhat complicated MR behavior in the falling part suggests the existence of a local minimum configuration during the switching of Co(10 nm) layers. The switching behavior of magnetic layers with interlayer dipole coupling was studied by micromagnetic simulations. Markedly different switching field of Co layers can be attributable to the variation of the dipole fields at each layer. (C) 2003 American Institute of Physics.

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Size dependence of switching current and energy barrier in the magnetization reversal of rectangular MRAM cell

Y. Nozaki, and K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  93 （ 10 ） 7295 – 7297 2003年05月

研究論文（学術雑誌）, 共著, 査読有り

Switching behavior of cross contacting CPP-GMR structure fabricated by two-step ion milling technique

H. Oishi, Y. Nozaki, K. Matsuyama

Journal of Applied Physics （The American Institute of Physics）  93 （ 10 ） 7613 – 7615 2003年05月

研究論文（学術雑誌）, 共著, 査読有り

Size dependence of switching current and energy barrier in the magnetization reversal of rectangular magnetic random access memory cell

Y Nozaki, K Matsuyama

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  93 （ 10 ） 7295 - 7297 2003年05月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

Write operation in magnetic random access memory (MRAM) with bit density of Gbit/cm2 order has been numerically simulated for low submicron scale magnetic cells. The amplitude of both the switching current I-w and the energy barrier DeltaE of the magnetic cell show strong dependence on the width w and the thickness t of the cell. The calculated results show that the amplitude of I-w is proportional to t/w, while that of DeltaE is proportional to wt(2). To obtain the sufficient energy barrier against a thermal stability (DeltaE&gt;80k(B)T, at 300 K), the thicker magnetic cell is required as the cell is downsized for high-density memory applications, although the thinner one is preferred to lower the switching current. From the calculated results, it appears that the margin of the switching current for selective write operation is decreased with decreasing the lateral aspect ratio of the cell. The addressability for the write operation is also degraded by the formation of structural defect in the cell. In this article, optimum configurations of the magnetic cell applicable for Gbit MRAM are discussed. (C) 2003 American Institute of Physics.

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Gbit級MRAM機能動作の計算機シミュレーション

能崎幸雄, 松山公秀

電子情報通信学会技術研究報告 （電子情報通信学会）  102 （ 723 ） 35 – 40 2003年03月

研究論文（学術雑誌）, 共著, 査読有り

Selective writing of sub-um2 domains in spin valve strip with current coincident scheme

K. Matsuyama, Y. Nozaki, J. Kikuchi

Proceedings of International Workshop on Informations & Electrical Engineering (IWIE 2002) （Kyunghee University）  36 （ 5 ） 152 – 157 2002年05月

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

Magnetization switching properties of sub-micron scale relief-structured GMR materials

Y. Nozaki, K. Matsuyama, S. Ishii

Proceedings of International Workshop on Informations & Electrical Engineering (IWIE 2002) （Kyunghee University）  2001   146 – 151 - 18 2002年05月

研究論文（学術雑誌）, 共著, 査読有り

Magnetoresistive measurement of switching behavior in nano-structured magnetic dot arrays

K. Matsuyama, Y. Nozaki, T. Misumi

Journal of Magnetism and Magnetic Materials （Elsevier）  239 （ 1-3 ） 11 – 13 2002年03月

研究論文（学術雑誌）, 共著, 査読有り

Spin dependent CPP transport properties of semiconductive-oxide/ferromagnet multilayers

Y. Nozaki, Y. Maeda, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  239 （ 1-3 ） 157 – 159 - 159 2002年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

The spin-dependent CPP (current perpendicular to plane) transport properties in semiconductive-oxide(MOx)/ ferromagnet multilayers consisting of CoPt/Co/MOx/Co/MOx/Co/CoPt, where M = Ti, Sn, were investigated by magneto-transport measurement. The XRD patterns reveal that the structures of sputtered MOx films are amorphous or nanocrystalline. The MR ratio of a TiOx-based multilayer (0.43%) was much smaller than that of a SnOx- based one (2.0%) at T = 77 K. As inferred from the shape of MR curves with a large saturation field above 4 kOe, suppressed MR change in the TiOx-based multilayer is caused by the interlayer diffusion of Co atoms into the TiOx layer. The same behavior was not observed in the SnOx-based one. The MR ratio was reduced by half on increasing t(SnOx) from 4 to 8 nm. This decrease can be ascribed to the scattering of the spin-polarized electron in the SnOx layer. (C) 2002 Elsevier Science B.V. All rights reserved.

Sub-micron scale relief structures of GMR materials fabricated by half-milling control

Y. Nozaki, T. Misumi, and K. Matsuyama

Journal of Magnetism and Magnetic Materials （Elsevier）  239 （ 1-3 ） 237 – 239 - 239 2002年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

We have investigated the magneto-transport properties of a GMR material consisting of CoPt(10nm)/Cu(10nm)/ NiFe(6nm) in which only the top NiFe layer is patterned by the half-milling technique. The top NiFe film was structured into a two-dimensional particle array with lateral dimensions of w = 0.2 mum and aspect ratio L/w = 1, 2 4 or 8. From MR measurements, the remanent magnetization of the NiFe particle array was found to gradually decrease with L/w, which can be ascribed to the relative increase of an end domain area in the particles, The longitudinal switching field H-swt markedly decreases as L/w &lt; 2. From the micromagnetic simulation, it was found that the decrease of H-swt was caused by the change of switching configuration from an edge reversal to a coherent rotation with decreasing L/w. (C) 2002 Elsevier Science B.V. All rights reserved.

MR measurement of sub-micron relief structures fabricated in GMR material

K. Matsuyama, Y. Nozaki, and T. Misumi

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  37 （ 4 ） 2114 – 2116 2001年07月

研究論文（学術雑誌）, 共著, 査読有り

Sub-micron GMR sensor with vertically integrated hard magnetic biasing applicable for high temperature

K. Matsuo, K. Matsuyama, and Y. Nozaki

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  37 （ 4 ） 2001 – 2003 2001年07月

研究論文（学術雑誌）, 共著, 査読有り

Sub-micron GMR sensors with vertically integrated hard magnet biasing applicable for high temperature operation

K Matsuo, K Matsuyama, Y Nozaki

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  37 （ 4 ） 2001 - 2003 2001年07月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

This paper demonstrates high-temperature operation of a sub-micron GMR sensor, biased with a vertically integrated hard magnet. In the present study, fringe fields from vertically integrated CoPt pattern are used for biasing transverse to the short axis of the GMR strip. While, well-defined shape anisotropy in the narrow strip pattern is used for biasing parallel to the short axis. A sputtered Co/Cu multilayer overlaid with CoPt is structured into strip pattern with a width of down to 0.4 mum by electron beam lithography and Ar ion milling. A typical layer structure of the studied samples is [Co(2.0 mn)/Cu(2.0 mn)]/ Ta(8.0 nm)/CoPt(23 nm). The fabricated self-biased GMR strip exhibited superior linear MR response to alternative external fields ranged from 0.4 to 250 Oe at room temperature and 553 K (apparatus limit).

MR measurement of sub-micron scale relief structures fabricated in GMR materials

K Matsuyama, Y Nozaki, T Misumi

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  37 （ 4 ） 2114 - 2116 2001年07月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

Understanding of magnetization process in patterned thin films is important for their applications in downsizing various magnetic devices. This paper deals with an experimental technique which enables us to characterize magnetization process in the ends of patterned ultra-thin films. In this study, only the top layer of magnetic sandwich structures were patterned into an array of fine magnetic particles using electron beam lithography and Ar ion milling to form relief structures in the films. The magnetization process of the arrays was inferred from magnetoresistance (MR) measurements of the films. MR behaviors of particle array samples of substrate/FM1/Cu/FM2 (FM1, FM2 = Co, NiFe, CoPt) in different pattern widths of omega = 0.2 and 0.6 mum, lengths L ranging from 0.2 to 280 mum and thicknesses of t = 6 and 18 mn were studied. From longitudinal MR measurements, a distinct decrease in remanent magnetization was found for sub-mum particle arrays, which may be associated with the formation of edge domains in the particles.

Selective writing of sub-um2 domain in spin valve strip with current coincident scheme

K. Matsuyama, N. Murashima, and Y. Nozaki

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  36 （ 5 ） 2767 – 2769 2000年09月

研究論文（学術雑誌）, 共著, 査読有り

Selective writing of sub-mu m(2) domain in spin valve strip with current coincident scheme

K Matsuyama, N Murashima, M Higashidani, Y Nozaki

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  36 （ 5 ） 2767 - 2769 2000年09月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

Cooperative nucleation of sub-mum(2) domains has been performed for a spin valve strip (0.4 mum width) of NiFe/Co/Cu/Co overlaid with orthogonal two-layer conductors (write and assist conductors). The current induced MR change due to the write current I-w markedly increases with the additional assist current I-a. Threshold value of I-w, required for domain nucleation was decreased from 15 mA/mum to 9 mA/mum by the application of I-a with an amplitude of 10 mA/mum, which confirms selective writing with the current coincident scheme. The cooperative effect disappears, when the phase difference between I-w and I-a becomes larger than the pulse width of 30 ns, Which can be associated with the fast relaxation time of the magnetization process in the sub-mum(2) region.

Magnetic properties of nanostructured wires deposited on the side edge of patterned thin film

K. Matsuyama, S. Komatsu, and Y. Nozaki

Journal of Applied Physics （The American Institute of Physics）  87 （ 9 ） 4724 – 4726 - 4726 2000年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

In the present study, magnetic nanowires with various cross-sectional dimensions have been fabricated by evaporating a magnetic material on the side edges of the patterned nonmagnetic thin film. The method allows the lengths of the two short axes to be defined precisely by controlling the thickness of the oxide (W-x) and magnetic material (W-y). The MFM images of the produced Co wires (2 mu m length) with dimensions of W-x=W-y=200 nm and W-x=W-y=50 nm present the single domain configuration. The MFM and magnetoresistance (MR) measurement demonstrate that the longitudinal magnetization switching field increases with the decrease of W-x and W-y, which becomes 1.3 kOe for wires with W-x=W-y=50 nm. The profile of the MR hysteresis suggests that considerable coherent rotation takes place before the irreversible longitudinal switching. Transverse saturation fields larger than 6 kOe were measured in the orthogonal two short axis directions, which confirms the successful fabrication of three-dimensional wires with comparable cross-sectional dimensions. (C) 2000 American Institute of Physics. [S0021-8979(00)60608-4].

Linear giant magnetoresistance behavior of submicron scale Co/Cu multilayer strips with antiferromagnetic coupling

K. Matsuyama, K. Matsuo, and Y. Nozaki

Journal of Applied Physics （The American Institute of Physics）  87 （ 9 ） 5359 – 5361 - 5361 2000年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Linear magntoresistance (MR) response of Co/Cu multilayer strips with sub-mu m width has been performed with a field sensitivity of sub-Oe. The orthogonal spin orientation for neighboring Co layers is initiated with an additional external field applied along the short axis of the strip. The thickness of the Cu layer was optimized to be 2.1 nm, at which the MR ratio of the as grown sample took a maximum value. The MR ratio of the as-grown film of [Co(2 nm)/Cu(2.1 nm)](3)/Co(2 nm)/Cu(2 nm) was 12.4%. The multilayer was patterned into strips with the pattern width w down to 0.2 mu m by means of electron beam lithography and Ar ion milling. The measured maximum MR ratio of the strips with w=0.4 and 0.2 mu m were 9.3% and 8.2%, respectively. The observed parabolic MR profile shows good agreement with the micromagnetic simulation assuming the symmetric scissors motion of the magnetization in the multilayer. A linear MR response was observed in a giant MR strip with 0.4 mu m width by applying alternating external fields, ranged from 0.1 to 10 Oe, under a transverse bias field of 300 Oe. (C) 2000 American Institute of Physics. [S0021-8979(00)54908-1].

Micromagnetic structure analysis of head-on-head type 180° domain wall in submicron size Co wires

Y. Nozaki, K. Matsuyama, T. Ono, H. Miyajima

Japanese Journal of Applied Physics （The Japan Society of Applied Physics）  38 （ 11 ） 6282 – 6286 - 6286 1999年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-4922

　概要を見る

Micromagnetic structures of the 180 degrees domain wall in submicron-size ferromagnetic Co wires were investigated by means of magnetic force microscopy. The domain waif width delta (similar to mu m) observed in the Co wire is about 10 times larger than that observed in Co films of the same thickness. From micromagnetic calculations using the Landau-Lifshitz-Gilbert (LLG) equation, the magnetic structure of the 180 degrees domain wall is expected to be a large vortex accompanied by a magnetic ripple structure. This complicated 180 degrees domain wall is formed to reduce the demagnetizing energy due to a head-on-head configuration of the magnetization, which results in a micron-scale transition area of the domain wall. The wire width dependence of the 180 degrees domain wall width obtained by micromagnetic calculations is almost consistent with that measured from the magnetic force micrograph.

Magnetic and electric properties of Sn-oxide/M (M=Fe, Ni, Co) multilayers

K. Matsuyama, K. Nishihata, S. Komatsu, and Y. Nozaki

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  35 （ 5 ） 2901 – 2903 - 2903 1999年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0018-9464

　概要を見る

Magnetic and electronic properties of novel semiconductive-oxide/ferromagnet multilayers of Sn-oxide and ferromagnetic metals (Fe, Ni, Co), deposited with a multi-target rf magnetron sputtering system, were studied. Among the studied material systems, Co/Sn-oxide sustains well-defined layer structure and ferromagnetic property for the thinnest thickness of 1 nm, A thermionic CPP transport was observed in [Co(2 nm) /Sn-oxide (4 nm)](10), which activation energy was evaluated as 4.4x10(-3) erg from the thermal dependence of conductivity. Negative magnetoresistance was observed in two orthogonal directions of in-plane external fields, which confirms spin dependent transport in Sn-oxide thin film, The measured MR change is 0.6 % (Delta R = 0.8 Omega, R-s=140 Omega) at room temperature.

Controlling of sub-um^2 domain in spin valve strip with conductor current

K. Matsuyama, Y. Hosokawa, and Y. Nozaki

IEEE Transactions on Magnetics （The Institute of Electrical and Electronics Engineering）  35 （ 5 ） 2826 – 2828 1999年09月

研究論文（学術雑誌）, 共著, 査読有り

Controlling of sub-mu m(2) domains in spin valve strips with conductor current

K Matsuyama, H Hosokawa, Y Nozaki

IEEE TRANSACTIONS ON MAGNETICS （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  35 （ 5 ） 2826 - 2828 1999年09月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0018-9464

　概要を見る

Nucleation and erasing of sub-mu m(2) domains in spin valve strips have been performed with current pulses applied through conductors, A spin valve material of NiFe/Co/Cu/Co was deposited by magnetron sputtering and patterned into sense lines of 40 parallel strips with 0.4 mu m width and 2 mu m pitch. Selective domain nucleation under parallel conductors with 1 mu m width and 2.6 mu m pitch has been confirmed by the current induced MR change, Pulses with opposite polarity performed erasing of nucleated domains. Reproducible MR change with a variation of +/-10 % relative to the mid value was realized in 10(4) operations of the domain nucleation process.

Effect of material parameters on magnetization process in microstructured thin film

K. Matsuyama, F. Nakamura, and Y. Nozaki

Journal of Magnetism and Magnetic Materials （Elsevier）  198-199   248 – 250 - 250 1999年06月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Effects of material parameters on the magnetization process in a sub-micron strip pattern have been studied by micromagnetic simulations. A grain structure in the thin film is modeled by a discretized square element array. A structural parameter is introduced considering discontinuous film structure. The exchange stiffness is also varied as parameters. Simulated transverse susceptibility chi and the longitudinal magnetization reversal field H(rev) in continuous film structure are somewhat smaller than the analytical predictions based on the coherent rotation model. The values of chi and H(rev) significantly decrease with the decrease of inter-grain coupling due to discontinuous structure. Numerical analysis for transients of the internal energy during the magnetization process reveals that the demagnetizing term dominates the transverse magnetization process. While, the demagnetizing and exchange energy terms comparatively contribute to the potential barrier for the longitudinal magnetization reversal. Various types of micromagnetic configurations of edge-curl, buckling and vortex were observed in the magnetization reversal depending on the material parameters. (C) 1999 Elsevier Science B.V. All rights reserved.

Geometrically induced giant magnetoresistance behavior in quarter-micrometer strip pattern

K. Matsuyama, K. Matsuo, and Y. Nozaki

Journal of Applied Physics （The American Institute of Physics）  85 （ 8 ） 5474 – 5476 - 5476 1999年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

The present article reports a geometrically induced magnetoresistance (MR) behavior observed in magnetic strips consisting of a symmetric layer structure with lateral sizes down to 0.2 mu m. The MR ratio was markedly improved from 2.8% for an as-grown film of Co(6 nm)/Cu(6 nm)/Co(6 nm) to 4.6% by structuring it into a strip with 0.3 mu m width. The parabolic MR behavior observed in the hard-axis direction suggests that the magnetization in the two magnetic layers rotates toward the opposite directions, which can be explained by the magnetostatic interaction between the surface magnetic charges at the pattern edges. The dependence of MR saturation field on the pattern width agrees well with a theoretical prediction based on a coherent rotation model. The MR ratio was markedly increased by the increase of the layer number and the thickness of the magnetic layer, the highest value of 7.8% was obtained for a strip made of [Co(6 nm)/Cu(4 nm)](2) Co(6 nm). A linear- and hysteresis-free MR response was performed with an alternative field modulation under a transverse bias field. (C) 1999 American Institute of Physics. [S0021-8979(99)63008-0].

ミクロンサイズ強磁性細線における180°対向磁壁の磁気構造

能崎幸雄, 小野輝男, 宮島英紀, 松山公秀

Journal of the Magnetics Society of Japan （日本磁気学会）  23 （ 4-2 ） 1121 – 1124 - 1124 1999年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0285-0192

　概要を見る

The micromagnetic structure of the 180° domain wall in submicron-size ferromagnetic Co wires was investigated by means of magnetic force microscopy. The wall width δ (∼μm) observed in Co wire is much larger than that observed in Co films of the same thickness. From micromagnetic calculation using the Landau-Lifshitz-Gilbert (LLG) equation, the magnetic structure of the 180° wall is expected to be a large vortex accompanied by a magnetic ripple structure. This complicated 180° wall is formed to suppress the demagnetizing energy due to a head-on-head configuration of the magnetization, which results in a micron-scale-wide transition area of the wall. The wire-width dependence of the 180° wall width obtained by micromagnetic calculation is almost consistent with that measured from the magnetic force micrograph.

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Magnetic domain structure of micron-size Co line array

Y. Nozaki, T. Ono, H. Miyajima, K. Matsuyama

Journal of the Magnetics Society of Japan （The Magnetics Society of Japan）  23 （ 1-2 ） 658 – 660 - 660 1999年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0285-0192

　概要を見る

The magnetic domain structure of lithographic Co line (1μm×280μm×70 nm) arrays was investigated in terms of a shape effect. The strong shape anisotropy along the Co line plays an important role in the formation of the magnetic domain structure. The magnetic stray field distribution above the Co line array was measured by using magnetic force microscope (MFM). As the magnetization of the Co line was saturated along the line, the stripe domain structure was observed. The direction of the magnetic moment was periodically modulated along the mean magnetization direction. The periodicity (λ= 0.8μm) is much longer than that of the magnetic ripple structure (∼10 nm) which is generally observed in the polycrystalline ferromagnetic Co thin film. The stripe domain structure is caused by the competition between the crystalline anisotropy perpendicular to the film plane and the shape anisotropy of the line.

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サブμｍ幅磁性多層膜細線の磁気抵抗特性

松尾 健一, 松山 公秀, 能崎 幸雄

日本応用磁気学会誌 （The Magnetics Society of Japan）  23 （ 4 ） 1249 - 1252 1999年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0285-0192

　概要を見る

GMR-like behavior was observed in magnetic strips consisting of a symmetric layer structure with pattern widths down to 0.2 μm, and was significantly different from that observed in as-grown samples. The dependence of the MR saturation field on the pattern width agrees well with a theoretical prediction based on a coherent rotation model. The MR ratio was markedly increased by increasing the number of layers and the thickness of the magnetic layers; the highest value of 7.8% was obtained for a strip made of [Co(6 nm)/Cu(4 nm)]₂/Co(6 nm). A linear and hysteresis-free MR response was obtained with an alternating field modulation under a transverse bias field. A thickness dependence of the GMR property implies that the probable cause of the antiparallel spin orientation in the strip pattern is magnetostatic interaction between the surface magnetic charges at the pattern edges.

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Magnetic and electric properties of SnOx/M (M=Fe, Ni, Co) multilayers

Kimihide Matsuyama, Katsunori Nishihata, Shinya Komatsu, Yukio Nozaki

Digests of the Intermag Conference （IEEE）  1999年

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0074-6843

　概要を見る

Discussed is a spin dependent current perpendicular to plane (CPP) transport observed in a novel semiconductive-oxide/ferromagnet multilayers of [SnOx(6 nm)/M(t nm)×10 (M=Fe, Ni, Co), deposited with a multi-target magnetron sputtering system. This transport property is dominated by the local region of the current path, where the magnetostatic coupling due to the interlayer roughness causes the antiparallel spin configuration in the remanence state.

Magnetization reversal process in micron size ferromagnetic Co line array

Y. Nozaki, T. Ono, K. Motohashi, H. Miyajima, and T. Kinoshita

Journal of Magnetism and Magnetic Materials （Elsevier）  177   1271 – 1272 - 1272 1998年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

The magnetization reversal process in a lithographic Co line array was investigated. The coercive force parallel to the Co line increases with the spacing between the Co lines. (C) 1998 Elsevier Science B.V. All rights reserved.

パルス磁場を用いたＢｉ系酸化物超伝導体における磁束の粘性力の測定

小林心, 能崎幸雄, 宮島英紀,本橋一成, 木下岳司

Journal of the Magnetics Society of Japan （日本応用磁気学会）  21 （ 4-2 ） 397 – 400 1997年04月

研究論文（学術雑誌）, 共著, 査読有り

Magnetic flux penetration process in two-dimentional superconductor covered with ferromagnetic particle array

Y. Nozaki, Y. Otani, K. Runge, H. Miyajima, B. Pannetier, J. P. Nozieres, and G. Fillion

Journal of Applied Physics （The American Institute of Physics）  79 （ 11 ） 8571 – 8577 1996年06月

研究論文（学術雑誌）, 共著, 査読有り

Magnetic flux penetration process in two-dimensional superconductor covered with ferromagnetic particle array

Y Nozaki, Y Otani, K Runge, H Miyajima, B Pannetier, JP Nozieres, G Fillion

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  79 （ 11 ） 8571 - 8577 1996年06月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

The magnetostatic effect of a ferromagnetic particle array on an underlying two-dimensional superconducting Nb thin film was investigated in terms of flux penetration processes by means of high sensitive magnetometry. For bare Nb film, a large drop in magnetization due to a flux rearrangement appeared in the low field region below 2.5 mT. However, once magnetic particles were fabricated on the surface of the Nb film, the drop was not observed. In this configuration, the ferromagnetic particles seem to behave as flux guides for the external magnetic field, whereby the flux distribution inside the superconductor is well regulated. Furthermore, a periodical oscillation was observed in the hysteresis loops. This behavior is associated with a flux quantization in the regions where the superconductivity is suppressed by the stray field of the ferromagnetic particles. The local flux density distribution around the ferromagnetic particles was evaluated by using the London equation, and the magnetization curve of the Nb film with periodically modulated superconducting order parameter was calculated. (C) 1996 American Institute of Physics.

試料共振型高感度磁力計

宮島英紀，本橋一成, 能崎幸雄, 大谷義近, 増田宏

Journal of the Magnetics Society of Japan （日本応用磁気学会）  20 （ 5 ） 919 – 921 1996年05月

研究論文（学術雑誌）, 共著, 査読有り

試料共振型磁力計による微小磁気モーメント測定

能崎幸雄, 宮島英紀，大谷義近，増田宏，本橋一成，眞砂卓史，K Runge

Journal of the Magnetics Society of Japan （日本応用磁気学会）  20 （ 2 ） 297 – 300 - 300 1996年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0285-0192

　概要を見る

A new type of highly sensitive magnetometer called a resonating sample magnetometer (RSM) is described. A magnetic sample is mounted on the end of a cantilever rod that incorporates a flat spring with a pick-up coil. The sample is magnetized in a de field, -5 kOe<<i>H</i>_a< +5 kOe,and is simultaneously subjected to a small ac field gradient.The ac field gradient exerts an alternating magnetic force on the sample, proportional to the sample's magnetic moment. The resulting oscillation of the rod is greatly amplified by using the mechanical resonance of the flat Elinvar spring, whose elastic modulus is almost constant in response to temperature variation. The deflection is measured by the pick-up coil. The RSM is considered as a possible system for measuring the temperature variation of magnetization. At room temperature, the sensitivity of the RSM is 6 × 10^-7 emu, and a complete hysteresis loop can be measured in about 15 min.

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超伝導体と軟磁性体の複合体の磁化特性

津山祥紀，大谷義近，眞砂卓史, 能崎幸雄, 宮島英紀

Journal of the Magnetics Society of Japan （日本応用磁気学会）  20 （ 2 ） 449 – 452 - 452 1996年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0285-0192

　概要を見る

The magnetization process of a hybrid system composed of a soft magnet (Fe-Si) and a superconductor (Bi₂Sr₂Ca₂Cu₃O_<i>x</i>) is investigated from the viewpoint of the magnetostatic coupling interaction. The residual magnetization of the hybrid system is higher than that of the superconductor, while the susceptibility is lower than that of the Fe-Si alloy. The behavior is interpreted as due to the occurrence of magnetic image in the superconductor and also to the magnetic flux pinning at the corner of the superconductor.

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Magnetostatic effect on magnetic flux penetration in superconducting Nb film covered with a micron-size magnetic particle array

Y. Nozaki, Y. Otani, K. Runge, H. Miyajima, B. Pannetier, and J. P. Nozieres

Journal of Applied Physics （The American Institute of Physics）  79 （ 8 ） 6599 – 6601 - 6601 1996年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-8979

　概要を見る

Magnetostatic effect of the micron-size ferromagnetic particle array on a two-dimensional superconductor was investigated. In the bare Nb film, a sharp drop in magnetization due to the flux rearrangement was observed, whereas this behavior was not observed for the Nb film with the ferromagnetic particles arranged on top. The difference in the magnetization curves may be attributed to the regulated flux penetration process by the ferromagnetic particle array. (C) 1996 American Institute of Physics.

High-resolution observation of magnetization processes in 2um x 2um x 0.04 um permalloy particles

K. Runge, Y. Nozaki, Y. Otani, H. Miyajima, B. Pannetier, T. Matsuda, and A. Tonomura

Journal of Applied Physics （The American Institute of Physics）  79 （ 8 ） 5075 – 5077 1996年04月

研究論文（学術雑誌）, 共著, 査読有り

High-resolution observation of magnetization processes in 2 mu mx2 mu mx0.04 mu m permalloy particles

K Runge, Y Nozaki, Y Otani, H Miyajima, B Pannetier, T Matsuda, A Tonomura

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  79 （ 8 ） 5075 - 5077 1996年04月

筆頭著者, 最終著者, 責任著者, 査読有り,  ISSN  0021-8979

　概要を見る

The magnetization process in an array of 2 mu m x 2 mu m x 0.04 mu m permalloy particles fabricated on a 100 nm carbon membrane was investigated by means of high-resolution Lorentz microscopy and electron holography in magnetic fields parallel and perpendicular to the film surface. For perpendicular fields, the magnetization reversal was found to begin with the nucleation of a vortex which gradually transformed into a closure domain configuration. At the remanent state, the flux closure was achieved with the generation of a new type of doubled domain wall. (C) 1996 American Institute of Physics.

Hydrogenation characteristics and magnetic properties of fine Ni particles coated with Pd

Y. Otani, H. Miyajima, M. Yamaguchi, Y. Nozaki, T. Manago, A. J. Fagen, and J.M.D. Coey

Journal of Magnetism and Magnetic Materials （Elsevier）  140-144   403 – 404 - 404 1995年02月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Hydrogenation characteristics and magnetic properties of Ni fine particles with thin Pd shell were investigated. The Pd shell appeared to turn weakly ferromagnetic below about 20 K, but this magnetic polarization was suppressed by hydrogenation.

Magnetic flux penetration process in superconducting Nb film covered with lithographic array of ferromagnetic particles

Y. Otani, Y. Nozaki, H. Miyajima, B. Pannetier, M. Ghidini, J.P. Nozieres, G. Fillion, and P. Pugnat

Physica C （Elsevier）  235-240   2945 – 2946 - 2946 1994年12月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0921-4534

　概要を見る

The effect of a micron size Sm33Co67 or Fe-Ni ferromagnetic particles array fabricated on a 2D superconducting niobium film was investigated by means of a magnetoresistivity measurement and rotating SQUID magnetometry. The magnetic particles seem to act as flux accumulators or flux guides through which flux lines penetrate inio the superconducting Nb film.

Magnetic properties of fine Ni particles coated with Pd

Y. Otani, H. Miyajima, M. Yamaguchi, Y. Nozaki, A. J. Fagen, and J.M.D. Coey

Journal of Magnetism and Magnetic Materials （Elsevier）  135 （ 3 ） 293 – 297 - 297 1994年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0304-8853

　概要を見る

Magnetic properties of Ni fine particles (0.7 mu m in diameter) coated with Pd (5-30 nm thick) were studied before and after hydrogenation. The system offers the possibility of studying hydrogenation under isovolumetric constraint, but this seems to produce little change in the saturation loading. The Pd shell appears to turn weakly ferromagnetic below about 20 K under high magnetic fields, but this magnetic polarization is suppressed by hydrogenation. The lowering of the magnetization of Ni by Pd coating may be related to a change in the surface anisotropy of Ni.