論文 - 能崎　幸雄

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<100>(100) parallel to MgO<110>(100) was achieved at a practical growth rate of 0.73 nm/s. The M-H hysteresis measured along Fe<100> directions exhibits a superior squareness with a low coercivity (H-c = 5 Oe). The saturation field along <110> 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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