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論文

Interaction between surface acoustic waves and spin waves in a ferromagnetic thin film

山本慧; Xu, M.*; Puebla, J.*; 大谷義近*; 前川禎通*

Journal of Magnetism and Magnetic Materials, 545, p.168672_1 - 168672_10, 2022/03

https://doi.org/10.1016/j.jmmm.2021.168672

被引用回数：3 パーセンタイル：45.08(Materials Science, Multidisciplinary)

We present a theoretical description of magnon-phonon interactions in a multi-layer structure containing a ferromagnetic thin film. The formalism is applicable to an arbitrary direction of external magnetic field and various types of acoustic waves including Rayleigh and Love surface modes. A particular attention is paid to the spatial profile of the acoustic wave modes and analytical expressions for the effective coupling coefficients are derived taking into account the degree of mode profile overlap between spin waves and acoustic waves. The results are applied to reproduce a strongly anisotropic and non-reciprocal linewidth of acoustic ferromagnetic resonance reported in a recent experiment.

論文

Holographic dual approach to magnetism and magnetization dynamics

横井直人*; 齊藤英治

Journal of Magnetism and Magnetic Materials, 545, p.168673_1 - 168673_12, 2022/03

https://doi.org/10.1016/j.jmmm.2021.168673

被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)

We propose a dual gravitational theory corresponding to isotropic ferromagnetic systems based on the holographic duality, and establish the holographic dictionary between physical quantities in ferromagnets and the gravitational theory. Utilizing the holographic dictionary, the holographic calculation in the dual gravitational theory is shown to reproduce thermodynamics of ferromagnets including ferromagnetic phase transitions and low-temperature behaviors originating from magnons and conduction electrons. We further derive the equation for magnetization dynamics in ferromagnets from the equations for scalar fields and non-abelian gauge fields on charged black holes in the dual gravitational theory. From these results, the holographic duality is expected to give a new guiding principle to explore new phenomena in spintronics and magnonics based on the gravitational perspective.

論文

Spin Hall magnetoresistance in Pt/CrO/YIG structure

Qi, J.*; Hou, D.*; Chen, Y.*; 齊藤英治; Jin, X.*

Journal of Magnetism and Magnetic Materials, 534, p.167980_1 - 167980_6, 2021/09

https://doi.org/10.1016/j.jmmm.2021.167980

被引用回数：1 パーセンタイル：16.71(Materials Science, Multidisciplinary)

Temperature dependence of the spin Hall magnetoresistance (SMR) has been investigated herein Pt/CrO/YFeO $_{12}$ structure. Well below the Nel temperature of CrO, the SMR is not observed at the noise level of 1.2 ppm. In vicinity of the Nel temperature, only a positive SMR tracks the YIG magnetic switching process, supporting that the SMR of normal metal/antiferromagnetic insulator/ferromagnetic insulator trilayer is controlled by the Nel vector of the antiferromagnetic insulator. A high field magnetoresistance is observed up to an external magnetic field of 20000 Oe which has a field angle dependence symmetry consistent with the SMR. We attribute this high field magnetoresistance to be induced by the Hanle magnetoresistance in Pt.

論文

Crystalline dependence of spin transmission in CrO thin films

Qin, J.*; Hou, D.*; Chen, Y.*; 齊藤英治; Jin, X.*

Journal of Magnetism and Magnetic Materials, 501, p.166362_1 - 166362_4, 2020/05

https://doi.org/10.1016/j.jmmm.2019.166362

被引用回数：3 パーセンタイル：27.83(Materials Science, Multidisciplinary)

Spin transmission in CrO films of different crystalline textures is studied experimentally. With YFeO $_{12}$ /CrO/Pt trilayer devices, a spin current is injected into CrO by spin pumping from YFeO $_{12}$ , and the spin transmission is monitored by the inverse spin Hall voltage ( $V_mathrm{ISHE}$ ) in Pt. For (0001) plane textured CrO films, $V_mathrm{ISHE}$ vanishes quickly below the Nel temperature. However, the $V_mathrm{ISHE}$ shows a broad shoulder below the Nel temperature for and plane co-textured CrO. Such a difference in the temperature dependence of CrO can be understood by the different Nel vector orientations with respect to the injected spin moment direction.

論文

Skyrmion-generated spinmotive forces in inversion broken ferromagnets

山根結太*; 家田淳一

Journal of Magnetism and Magnetic Materials, 491, p.165550_1 - 165550_5, 2019/12

https://doi.org/10.1016/j.jmmm.2019.165550

被引用回数：3 パーセンタイル：13.64(Materials Science, Multidisciplinary)

We present an analytical study on the spinmotive force (SMF) generated by translational motion of magnetic skyrmion. A SMF refers to an electrical voltage induced by dynamical magnetic textures, which reflects the spatiotemporal variation of the magnetization. The dynamics of a skyrmion thus can be detected by a SMF measurement, which may play an important role in future skyrmion-based technologies. We find the dependence of the SMF on skyrmion structure (e.g., skyrmion or anti-skyrmion, Neel or Bloch type, and the polarity of the skyrmion core) and Rashba and Dresselhaus spin-orbit couplings (SOCs). To this end, we derive explicit formulae for the spin-dependent electric fields originating from the two SOCs. Our findings offer a comprehensive understanding of the phenomenon and an estimation of the electrical voltage signal associated with a moving skyrmion for a given experiment.

論文

Magnetic excitations and transport properties in frustrated ferromagnetic chain

大西弘明

Journal of Magnetism and Magnetic Materials, 479, p.88 - 90, 2019/06

https://doi.org/10.1016/j.jmmm.2019.02.006

被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)

In a spin nematic state of a spin-1/2 frustrated ferromagnetic chain, low-energy excitations are governed by bound magnons, so that bound magnons carry spin current and thermal current. Regarding magnetic excitations, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-range longitudinal and short-range transverse spin correlations, respectively, while we observe gapless quadrupole excitations, signaling quasi-long-range quadrupole correlations. In the present work, we investigate spin and thermal transport properties by exploiting numerical methods, such as exact diagonalization and density-matrix renormalization group. We will discuss the effects of bound magnon propagation in spin and thermal transport, based on detailed analyses of current-current correlation functions in the spin nematic ground state, and temperature and field dependencies of the spin Drude weight and the thermal Drude weight.

論文

Microscopic formulation of nonlinear spin current induced by spin pumping

亀田麻衣*; 廣部大地*; 大門俊介*; 塩見雄毅*; 高橋三郎*; 齊藤英治

Journal of Magnetism and Magnetic Materials, 476, p.459 - 463, 2019/04

https://doi.org/10.1016/j.jmmm.2018.12.061

被引用回数：1 パーセンタイル：6.16(Materials Science, Multidisciplinary)

Nonlinear effects of spin pumping have been investigated by numerically calculating the temporal evolution of the magnon number affected by three- and four-magnon interactions. We showed that the three-magnon interaction gives rise to the enhancement of spin-pumping spin current. We also found that the four-magnon interaction in combination with the three-magnon interaction can be responsible for the experimentally observed low-frequency oscillation of spin current.

論文

Invariant incommensurate coherence length in spin-density-wave excitation of Cr $_{0.99}$ Fe $_{0.01}$

平賀晴弘*; 矢野真一郎*; 福田竜生

Journal of Magnetism and Magnetic Materials, 469, p.629 - 632, 2019/01

https://doi.org/10.1016/j.jmmm.2018.09.035

被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)

Low-energy magnetic excitation of spin-density wave (SDW) in a single crystal of Cr $_{0.99}$ Fe $_{0.01}$ was measured using cold neutron triple-axis spectroscopy. Because of the unchanged incommensurability and the constant line width in 2.5 6 meV, the magnetic excitation could not be explained with a conventional dispersion of . In this paper, we conjectured the presence of standing waves, which would be excited in local spin matrices. The effectively vertical dispersion was attributed to the longitudinal spin fluctuation in the spin matrices. A series of low-energy magnetic excitations in Cr alloys could be understood with the coexistence of the standing waves and progressive waves such as spin waves.

論文

Enhanced orbital magnetic moment in FeCo nanogranules observed by Barnett effect

緒方裕大; 中堂博之; Gu, B.; 小林伸聖*; 小野正雄; 針井一哉; 松尾衛; 齊藤英治; 前川禎通

Journal of Magnetism and Magnetic Materials, 442, p.329 - 331, 2017/11

https://doi.org/10.1016/j.jmmm.2017.06.101

被引用回数：6 パーセンタイル：54.9(Materials Science, Multidisciplinary)

The gyroscopic g factor, , of FeCo nanogranules embedded in a matrix of MgF (FeCo-MgF) was determined by measuring the magnetic-field generation from a rotating sample due to the Barnett effect. The value of the FeCo-MgF is estimated to be 1.76 0.11. The orbital contribution to the magnetic moment in the FeCo nanogranules was found to be quite large compared with that in bulk FeCo, being consistent with a density-functional-theory calculation that shows that the orbital magnetic moment may increase at the FeCo/MgF interfaces. The result suggests that the orbital magnetic moment is enhanced by symmetry breaking at the surface of the FeCo nanogranules.

論文

Three-dimensional magnetic domain structure in a model with exchange randomness

横田光史

Journal of Magnetism and Magnetic Materials, 432, p.532 - 538, 2017/06

https://doi.org/10.1016/j.jmmm.2017.02.031

被引用回数：1 パーセンタイル：6.72(Materials Science, Multidisciplinary)

Surface magnetic domain structure can be different from internal one. Both of them are influenced by structural randomness. Three-dimensional numerical simulations are performed using a model with random exchange interactions and dipolar interactions on a lattice with the periodic boundary condition for the horizontal directions to simulate infinite system in the directions and with the free boundary condition for vertical direction (z) to represent the existence of surface. The lattice sizes are for and for . To simulate highly anisotropic materials, time dependent Ginzburg-Landau equation using a model with Ising symmetry is solved numerically. Dependence of magnetic domain patterns on thickness of the system and the degree of disorder is investigated for systems with small thickness. Magnetic structure factor for the surface layer is compared with that for the internal layer. The inverse of the wave number that gives the maximum value of the magnetic structure factor depends on the thickness of the system as $T^{0.3}$ approximately. The distribution of the local magnetization depends on the disorder rather differently for different thicknesses of the system.

論文

The Study of the magnetization process of Fe film by magnetic Compton scattering and Mssbauer spectroscopy

安居院あかね; 増田亮*; 小林康弘*; 加藤忠*; 柄本俊*; 鈴木宏輔*; 櫻井浩*

Journal of Magnetism and Magnetic Materials, 408, p.41 - 45, 2016/06

AA2015-0849.pdf:1.54MB

https://doi.org/10.1016/j.jmmm.2016.02.016

被引用回数：4 パーセンタイル：23.27(Materials Science, Multidisciplinary)

本研究では磁気コンプトン散乱およびメスバーワー分光を用いてFe薄膜の磁化過程を詳細に調べた。磁気コンプトン散乱からスピン磁気モーメントと軌道磁気モーメントの磁化曲線を算出した。メスバーワースペクトルからは磁化と外部磁場のなす角の印加磁場依存性を調べた。これにより磁化曲線の振る舞いは磁化と外部磁場のなす角の変化と大きなかかわりがあることが分かった。

論文

What determines the sign of the spin Hall effects in Cu alloys doped with 5d elements?

Xu, Z.; Gu, B.; 森道康; Ziman, T.*; 前川禎通

Journal of Magnetism and Magnetic Materials, 400, p.184 - 187, 2016/02

https://doi.org/10.1016/j.jmmm.2015.08.073

被引用回数：4 パーセンタイル：23.27(Materials Science, Multidisciplinary)

We perform a systematical analysis of the spin Hall effect (SHE) in the Cu alloys doped with a series of 5d elements, by the combined approach of density functional theory and Hartree-Fock approximation. We find that not only the spin orbit interactions (SOI) in both the 5d and 6p orbitals, but also the local correlations in the 5d orbitals of the impurities, are decisive on the sign of the spin Hall angle (SHA). Including all of these three factors properly, we predict the SHA for each alloy in the series. The signs of CuIr and CuPt are sensitive to perturbation of the local correlations. This observation is favorable for controlling the sign of the transverse spin Hall voltage.

論文

Effects of exchange randomness on two-dimensional magnetic domain pattern formation

横田光史

Journal of Magnetism and Magnetic Materials, 385, p.119 - 123, 2015/07

https://doi.org/10.1016/j.jmmm.2015.03.015

被引用回数：1 パーセンタイル：5.16(Materials Science, Multidisciplinary)

Magnetic domain pattern formation is known to be influenced by structural disorder. We perform numerical simulations using a model of two-dimensional magnetic domain pattern formation focusing on effects of exchange randomness. The model is a scalar model with exchange and dipolar interactions, which includes disorder in the exchange interactions. Morphological change of the patterns with the increase in the disorder is observed. The distribution of the local magnetization becomes broader with the increase of the disorder. For a definite realization of the randomness, many patterns can appear.

論文

Current-induced spin polarization on a Pt surface; A New approach using spin-polarized positron annihilation spectroscopy

河裾厚男; 深谷有喜; 前川雅樹; Zhang, H.; 関剛斎*; 吉野達郎*; 齊藤英治*; 高梨弘毅*

Journal of Magnetism and Magnetic Materials, 342, p.139 - 143, 2013/09

https://doi.org/10.1016/j.jmmm.2013.04.006

被引用回数：19 パーセンタイル：64.33(Materials Science, Multidisciplinary)

電流通電下にある白金超薄膜表面におけるスピン偏極陽電子消滅を観測した。その結果、表面で形成されるオルソポジトロニウムの強度が通電方向に応じて変化することが明らかになった。この結果は、通電下において白金表面の伝導電子がスピン偏極していることを示唆している。その場合、伝導電子のスピン偏極率は1%以上であると推定される。

論文

Bias voltage dependence of tunneling magnetoresistance in granular C $_{60}$ -Co films with current-perpendicular-to-plane geometry

境誠司; 三谷誠司*; 松本吉弘; 圓谷志郎; Avramov, P.; 大伴真名歩; 楢本洋*; 高梨弘毅

Journal of Magnetism and Magnetic Materials, 324(12), p.1970 - 1974, 2012/06

https://doi.org/10.1016/j.jmmm.2012.01.033

被引用回数：3 パーセンタイル：15.52(Materials Science, Multidisciplinary)

Voltage-dependence of the tunneling magnetoresistance effect in the granular C $_{60}$ -Co films has been investigated under the current-perpendicular-to-plane geometry. The transport measurements demonstrate that the granular C $_{60}$ -Co films show unusually an exponential MR-V dependence. Small characteristic energies of less than 10's meV are derived from the temperature dependences of the characteristic voltage in the exponential relationship. Considering the voltage drops between Co nanoparticles and also the effect of cotunneling on the energy values, the characteristic energies for the voltage-induced degradation of the spin polarization are found to show a satisfactory agreement with that for the thermally-induced one. It can reasonably be expected that the onset of magnetic disorder to the localized d-electron spins at the interface region of the C $_{60}$ -Co compound with Co nanoparticles will lead to the unusual voltage and temperature dependence of the MR ratio and the spin polarization.

論文

Magnetic circular dichroism of [Co/Pd] and [CoB/Pd] multilayered films

安居院あかね; 朝日透*; 佐山淳一*; 水牧仁一朗*; 田中真人*; 逢坂哲彌*

Journal of Magnetism and Magnetic Materials, 320(22), p.3015 - 3018, 2008/11

https://doi.org/10.1016/j.jmmm.2008.08.011

被引用回数：1 パーセンタイル：6.48(Materials Science, Multidisciplinary)

膜製作温度260 $^{circ}$ Cで作成された[Co/Pd]及び[CoB/Pd]多層膜についてCo L吸収端において軟X線吸収測定及び磁気円2色性測定を行った。試料はPd相の厚さによって磁化方向が変わり測定はに垂直磁化を示す膜厚のものからPd相を厚くして面内磁化を示すものまでを測定した。Co相にBを添加した場合としない場合についてミクロスコピックな磁気的性質が変化したので報告する。

論文

Resonant X-ray magnetic diffraction experiments on SmBC

稲見俊哉; 本間徹生*; 筒井智嗣*; 犬童健太郎*; 小野寺秀也*; 石井賢司; 大和田謙二; 葛下かおり*; 中尾裕則*; 村上洋一*

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.748 - 750, 2007/03

われわれはSmBCの $T_{rm N2}$ =37Kと $T_{rm N1}$ =51Kの逐次相転移を共鳴X線回折で調べた。強い共鳴回折がSmの吸収端で $T_{rm N2}$ 以下では101反射に観測され、一方、中間相では、非整合な=(1, ,1)の位置に観測された(=0.13)。したがって、SmBCの逐次相転移は整合-非整合磁気相転移であることがわかった。

論文

Fractal dimension in percolating Heisenberg antiferromagnets

伊藤晋一*; 梶本亮一; Adams, M. A.*; Bull, M. J.*; 岩佐和晃*; 阿曽尚文*; 吉澤英樹*; 竹内徹也*

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1549 - 1551, 2007/03

三次元パーコレーション・ハイゼンベルク反強磁性体RbMnMg $_{1-c}$ Fにおける静的・動的性質を調べた。磁性イオン濃度がパーコレーション濃度に近い試料を用いて、超格子点近傍をネール温度より低い温度にて測定した。中性子回折実験により、弾性散乱成分の波数依存性は $q^{-x}$ でよく表されることがわかった。さらに非弾性中性子散乱によって磁気フラクトンを測定したところ、観測されたフラクトンはの分散関係を持つことがわかった。実験から求められた指数は及びであり、両者ともフラクタル次元とよく一致する。

論文

Magnetic penetration depth and self-induced irradiation effects in superconducting PuCoGa probed by muon spin rotation

大石一城; Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Bauer, E. D.*; Morales, L. A.*; Sarrao, J. L.*; MacLaughlin, D. E.*; Shu, L.*; 伊藤孝; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.566 - 568, 2007/03

PuCoGaは電子系超伝導体の中で最も高い超伝導転移温度 ${it T$_{rm c}$}$ =18.5Kを有する。また、放射性元素であるPuの崩壊により自己照射効果を受けるという特徴を有する。われわれは試料作成から400日が経過した単結晶試料( ${it T$_{rm c}$}$ =15.5K)を用いてSR測定を行い、磁場侵入長の温度依存性に対する自己照射効果の影響を調べた。その結果=0Kでの磁場侵入長は、作成から25日後の単結晶試料( ${it T$_{rm c}$}$ =18.5K)に比べ、1.8倍増大することが明らかとなった。一方で磁場侵入長の温度依存性は25日後の試料で観測された結果と同様、温度に線形に増大することから、自己照射効果により ${it T$_{rm c}$}$ は約18%減少したにもかかわらず、依然として波超伝導体の特徴が保持されていることを確認した。

論文

NMR observation of quadrupolar order parameter in NpO

徳永陽; 青木大*; 本間佳哉*; 神戸振作; 酒井宏典; 池田修悟; 藤本達也; Walstedt, R. E.*; 安岡弘志; 塩川佳伸*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.735 - 737, 2007/03

f電子系化合物の示す複雑で豊かな物性の背後には、f電子が持つ多極子の自由度が隠されている。この多極子の自由度が最も顕著に現れるのが多極子秩序と呼ばれる現象である。通常、多極子秩序と言った場合、電気的な四極子モーメントによる秩序を指すことが多い。ところが最近、二酸化ネプツニウムにおいて、四極子よりもさらに高次の多極子である八極子に起因する新しい磁気秩序の可能性が指摘され注目を集めている。講演では現在われわれが行っている二酸化ネプツニウム単結晶を用いた核磁気共鳴研究の最新の成果を中心に、この新奇な秩序相について紹介する。