研究者詳細 - 能崎　幸雄

論文 - 能崎　幸雄

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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

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

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 < 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

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

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

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

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

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

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

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

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

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

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

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

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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能崎 幸雄

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能崎　幸雄

論文 - 能崎　幸雄