論文 - 能崎　幸雄

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