研究者詳細 - 能崎　幸雄

論文 - 能崎　幸雄

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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

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

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

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

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

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

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

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

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

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

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

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

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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能崎 幸雄

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論文 - 能崎　幸雄