論文 - 山野井　一人

Spatiotemporal visualization of a surface acoustic wave coupled to magnons across a submillimeter-long sample by pulsed laser interferometry

Maezawa K, Fujii S, Yamanoi K, Nozaki Y, Watanabe S

Physical Review Applied （AMER PHYSICAL SOC）  21 （ 4 ）  2024年04月

研究論文（学術雑誌）, 共著,  ISSN  2331-7019

　概要を見る

Surface acoustic waves (SAWs) coupled to magnons have attracted much attention because they allow for the long-range transport of magnetic information that cannot be achieved by magnon alone. We employed pulsed laser interferometry to visualize the entire spatiotemporal dynamics of a SAW that travels on a nickel (Ni) thin film and is coupled to magnons. It was possible to trace the coupling-induced amplitude reduction and phase shift that occurs as the SAW propagates over a distance of 0.4 mm. The observed changes are consistent with results obtained from conventional radio-frequency transmission measurements, which probe the total SAW absorption due to magnon-phonon coupling. This result verifies that our method can accurately capture the spatiotemporal dynamics of a SAW coupled to magnons across the entire length of the sample. Additionally, we validated our time-resolved profiles by comparing them with theoretical results that take the echo wave due to reflection into account. The impact of the echo wave is significant even when it has propagated over a distance of the order of millimeters. Our imaging results highlight the visualization of the long-range propagation of the SAW coupled to magnons and offer more information about the surface vibration profiles in such devices.

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Y₃Fe₅O₁₂ film with multi-domain epitaxy on single-crystalline LiNbO₃ substrate

Yamanoi K, Hase K, Komori S, Taniyama T, Nozaki Y

APL Materials （AIP Publishing）  12 （ 2 ）  2024年02月

研究論文（学術雑誌）, 共著, 筆頭著者, 責任著者, 査読有り,  ISSN  2166-532X

　概要を見る

Y3Fe5O12 is one of the magnetic insulators that can realize high-speed and low-power-consuming spintronics devices. However, it is hard to prepare a high-quality Y3Fe5O12 film via a conventional sputtering process owing to its low crystalline texture, which leads to a crucial increase in the Gilbert damping constant. Moreover, a single crystalline Gd3Ga5O12 substrate, whose lattice constant is well matched with Y3Fe5O12, is indispensable to improve the crystallinity of the Y3Fe5O12 film. In this article, we demonstrated an epitaxial growth of multiple domains for a 30-nm-thick Y3Fe5O12 film by means of magnetron sputtering on a single crystalline 128° Y-X LiNbO3 substrate , which has been widely utilized in surface acoustic wave devices. From the pole figure of x-ray diffraction, an oblique epitaxial growth of Y3Fe5O12(400) is successfully observed on the 128° Y-X LiNbO3 substrate after a high-temperature post-annealing. The saturation magnetization is equivalent to the value of the epitaxial Y3Fe5O12 film on the Gd3Ga5O12 substrate. The relatively low effective Gilbert damping constant of 0.0039 also supports the high crystalline texture of the Y3Fe5O12 film. The developed growth technique will pave the way for the application of the Y3Fe5O12 film on magneto-acoustic devices.

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NiFe/Pt 2層膜の音響スピン注入の温度依存性

山野井一人, 鳥羽竜生, 能崎幸雄

電気学会研究会資料 23 （ 076 ）  2023年08月

研究論文（研究会，シンポジウム資料等）, 共著, 筆頭著者

A large modulation of spin pumping using magnetic phase transitions in single crystalline dysprosium

Kazuto Yamanoi, Yuri Sakakibara, Junji Fujimoto, Mamoru Matsuo, Yukio Nozaki

Applied Physics Express （IOP Publishing）  16 （ 6 ） 063004 - 063004 2023年06月

研究論文（学術雑誌）, 共著, 筆頭著者, 責任著者, 査読有り,  ISSN  18820778

　概要を見る

We report a large modulation of spin pumping using temperature-induced magnetic phase transitions in c-axis oriented single crystalline dysprosium (Dy). From the temperature variation of the magnetic susceptibility, transitions from paramagnetic (PM) to ferromagnetic (FM) phases via antiferromagnetic (AFM) phase are clearly observed in the Dy. Unlike polycrystalline Dy, the spin pumping of both PM- and AFM-Dy are strongly suppressed owing to the increased non-dissipative backflow of spin current by the long-range spin transport, although two orders of magnitude difference exist between FM- and AFM-phases.

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Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films

Hayato Nakayama, Taisuke Horaguchi, Cong He, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuto Yamanoi, Yukio Nozaki

Physical Review B （AMER PHYSICAL SOC）  107 （ 17 ）  2023年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  24699950

　概要を見る

We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic Ni95Cu5 alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.

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Enhancement of room-temperature unidirectional spin Hall magnetoresistance by using a ferromagnetic metal with a low Curie temperature

Yamanoi, K., Semizu, H., Nozaki, Y.

Physical Review B （AMER PHYSICAL SOC）  106 （ 14 ）  2022年10月

研究論文（学術雑誌）, 共著, 筆頭著者, 責任著者, 査読有り,  ISSN  24699950

　概要を見る

The unidirectional spin Hall magnetoresistance (USMR) effect is useful to detect the direction of magnetization in a ferromagnetic metal/nonmagnetic metal bilayer, which is the typical geometry used in a spin-orbit torque switching device. In this Letter, we demonstrate the enhancement of the USMR effect by reducing the Curie temperature TC of the ferromagnetic (FM) layer in a FM/platinum bilayer. The USMR ratio was maximized when the thickness of each FM layer was consistent with the spin diffusion length. We found that the maximum USMR ratio can be doubled by replacing Ni81Fe19 (TC=854 K) with Ni85Cu15 (TC=527 K) as the FM. This enhancement of the USMR effect is attributed to an increase of electron-magnon scattering in accordance with Bloch law. We also found that the use of ferromagnets with face-centered-cubic structures, such as Ni, Ni81Fe19, and Ni85Cu15, increased the USMR effect relative to that of body-centered-cubic Fe.

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Temporal-offset dual-comb vibrometer with picometer axial precision

A. Iwasaki, D. Nishikawa, M. Okano, S. Tateno, K. Yamanoi, Y. Nozaki, S. Watanabe

APL Photonics （AIP Publishing）  7 （ 10 ） 106101 - 106101 2022年10月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  2378-0967

　概要を見る

We demonstrate a dual-comb vibrometer where the pulses of one frequency-comb are split into pulse pairs. We introduce a delay between two pulses of each pulse pair in front of the sample, and after the corresponding two consecutive reflections at the vibrating sample surface, the initially introduced delay is canceled by a modified Sagnac geometry. The remaining phase difference between the two pulses corresponds to the change in the axial position of the surface during the two consecutive reflections. The Sagnac geometry reduces the effect of phase jitter since both pulses propagate through nearly the same optical path (in opposite directions), and spurious signals are eliminated by time gating. We determine the amplitude of surface vibration on a surface-acoustic-wave device with an axial precision of 4 pm. This technique enables the highly accurate determination of extremely small displacements.

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NiFe薄膜中の表面弾性波により励起されたスピン波強度の温度依存性

山野井一人, 鳥羽竜生, 能崎幸雄

電気学会研究会資料 21 （ 142 ）  2021年12月

研究論文（研究会，シンポジウム資料等）, 共著, 筆頭著者

Einstein-de Haas phase shifts in surface acoustic waves

Shoma Tateno, Yuki Kurimune, Mamoru Matsuo, Kazuto Yamanoi, Yukio Nozaki

PHYSICAL REVIEW B （AMER PHYSICAL SOC）  104 （ 2 ）  2021年07月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  24699950

　概要を見る

We demonstrate the phase shift of the Rayleigh-type surface acoustic wave (RSAW) in a ferromagnetic Ni81Fe19 film based on the gyromagnetic Einstein-de Haas (EdH) torque that can be attributed to the back action of spin-wave excitation. The EdH torque modulates the transverse velocity of the bulk acoustic wave that causes the bipolar phase shift of RSAW. When compared with a magnetoelastic torque, the phase shift can be more prominently enhanced by increasing the frequency. The gyromagnetic torque in the RSAW paves the way for controlling spin-mechatronics devices without magnetoelastic torque which is specific to a certain material.

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Growth, strain, and spin-orbit torques in epitaxial Ni-Mn-Sb films sputtered on GaAs

N. Zhao, A. Sud, H. Sukegawa, S. Komori, K. Rogdakis, K. Yamanoi, J. Patchett, J. W. A. Robinson, C. Ciccarelli, H. Kurebayashi

Physical Review Materials （American Physical Society）  5 （ 1 ）  2021年01月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  24759953

　概要を見る

We report current-induced spin torques in epitaxial NiMnSb films on a commercially available epiready GaAs substrate. The NiMnSb was grown by cosputtering from three targets using optimized parameters. The films were processed into microscale bars to perform current-induced spin-torque measurements. Magnetic dynamics were excited by microwave currents, and electric voltages along the bars were measured to analyze the symmetry of the current-induced torques. We found that the extracted symmetry of the spin torques matches those expected from spin-orbit interaction in a tetragonally distorted half-Heusler crystal. Both fieldlike and dampinglike torques are observed in all the samples characterized, and the efficiency of the current-induced torques is comparable to that of ferromagnetic metal/heavy-metal bilayers.

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Magnetic dynamics of quasi-Antiferromagnetic layer fabricated by 90° magnetic coupling

Shuu Horiike, Gen Nagashima, Yuichiro Kurokawa, Yongshi Zhong, Kazuto Yamanoi, Terumitsu Tanaka, Kimihide Matsuyama, Hiromi Yuasa

Japanese Journal of Applied Physics （IOP PUBLISHING LTD）  59 （ SG ）  2020年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00214922

　概要を見る

In this study, we fabricated quasi-Antiferromagnetic (AFM) layers and investigated the magnetic dynamics of quasi-AFM in both an experiment and simulation. Quasi-AFM has multi domains with alternating antiparallel magnetization, which can be realized by using 90° magnetic coupling between two ferromagnetic layers. In magnetic resonance measurement, a frequency and damping constant of CoFe-based quasi-AFM are higher than those of conventional CoFe. Likewise, in micromagnetic simulation, we obtained the spin torque oscillation in Quasi-AFM with high frequency. This suggests the possibility of a novel material with the high frequency wave generator without a stray field, like antiferromagnetic materials.

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Signature of spin-dependent Seebeck effect in dynamical spin injection of metallic bilayer structures

Kazuto Yamanoi, Minoru Yafuso, Keishi Miyazaki, Takashi Kimura

JOURNAL OF PHYSICS-MATERIALS （IOP PUBLISHING LTD）  3 （ 1 ）  2020年01月

研究論文（学術雑誌）, 筆頭著者, 査読有り

　概要を見る

The dynamical spin injection in a ferromagnetic/paramagnetic bilayer with various paramagnetic layers has been examined by using the inverse spin Hall effect. We adapt a CoFeB film as a ferromagnetic layer, which has a large spin dependent Seebeck coefficient. The contribution of the spin pumping was evaluated from the line-width change of the ferromagnetic resonant spectra while that of the thermal spin injection was evaluated from the heat conductivity for the paramagnetic layer. We find that the spin Hall voltage does not show the systematic change with respect to the line-width change. However, the normalized spin Hall voltage is found to increase with the heat conductivity for the paramagnetic layer. These results suggest that the thermal spin injection is a major contribution for the dynamical spin injection in CoFeB/paramagnetic bilayer systems.

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Thermal Spin-Valve Effect in Magnetic Multi-layered Nanowires

Nagarjuna Asam, Kazuto Yamanoi, Kohei Ohnishi, Takashi Kimura

Journal of Superconductivity and Novel Magnetism （SPRINGER）  32 （ 10 ） 3109 - 3113 2019年10月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  15571939

　概要を見る

We have investigated the influence of the spin-dependent scattering on the heat transports in NiFe/Cu/NiFe and Co/Cu/Co tri-layered nanowires. The thermal conductivity and its spin dependence for the tri-layered wires have been evaluated by using an integrated nano-sized thermo couple. We find that the thermal spin-valve effect is always approximately 8 times larger than the electrical spin-valve effect, namely giant magnetoresistance effect. The numerical simulation with the experimental results enable us to estimate the thermal conductivity for the tri-layered wire and its spin dependence. Surprisingly, the spin dependence of the thermal conductivity for the Co/Cu/Co wire is as high as 8%, which is much larger than the electrical one. This indicates a high potential application of the thermal spin-valve effect.

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Bolometric ferromagnetic resonance techniques for characterising spin-Hall effect at high temperatures

P. Phu, K. Yamanoi, K. Ohnishi, J. Hyodo, K. Rogdakis, Y. Yamazaki, T. Kimura, H. Kurebayashi

Journal of Magnetism and Magnetic Materials （ELSEVIER）  485   304 - 307 2019年09月

研究論文（学術雑誌）, 共著, 責任著者, 査読有り,  ISSN  03048853

　概要を見る

We report on current-induced ferromagnetic resonance techniques to characterise spin-Hall effect at high temperatures. A microwave current was injected into a patterned CoFeB/Pt bi-layer grown on a glass substrate, simultaneously exerting spin-transfer torques through the spin-Hall effect and also causing Joule heating enabling the control of the device temperature. We measured the device temperature by using the device itself as a local temperature sensor. A clear reduction of CoFeB magnetisation was observed as the device temperature was increased allowing us to estimate the Curie temperature of our CoFeB film to be 920 K. The spin-Hall angle of Pt was quantified as (1.72 ± 0.03) × 10−2 at 300 K and was slightly increased to (1.75 ± 0.02) × 10−2 at 410 K. This simple method can be widely used for quantifying the spin-Hall angle of a large variety of materials at high temperatures.

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Tunable magnetization dynamics in artificial spin ice via shape anisotropy modification

T. Dion, D. M. Arroo, K. Yamanoi, T. Kimura, J. C. Gartside, L. F. Cohen, H. Kurebayashi, W. R. Branford

Physical Review B （AMER PHYSICAL SOC）  100 （ 5 ）  2019年08月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  24699950

　概要を見る

Ferromagnetic resonance (FMR) is performed on kagome artificial spin ice (ASI) formed of disconnected Ni80Fe20 nanowires. Here we break the threefold angular symmetry of the kagome lattice by altering the coercive field of each sublattice via shape anisotropy modification. This allows for distinct high-frequency responses when a magnetic field is aligned along each sublattice and additionally enables simultaneous spin-wave resonances to be excited in all nanowire sublattices, unachievable in conventional kagome ASI. The different coercive field of each sublattice allows selective magnetic switching via global field, unlocking novel microstates inaccessible in homogeneous-nanowire ASI. The distinct spin-wave spectra of these states are detected experimentally via FMR and linked to underlying microstates using micromagnetic simulation.

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Modification of the magnetization dynamics of a NiFe nanodot due to thermal spin injection

Nagarjuna Asam, Kazuto Yamanoi, Takashi Kimura

Journal of Physics D: Applied Physics （IOP PUBLISHING LTD）  51 （ 22 ）  2018年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00223727

　概要を見る

An array of NiFe nanodots has been prepared on a Cu/CoFeAl film. Since a thermal spin current is expected to be excited owing to a large spin-dependent Seebeck coefficient for the CoFeAl, we investigate the magnetization dynamics of the NiFe dots under the temperature gradient along the vertical direction. By using vector network analyzer measurements, we have demonstrated that the temperature gradient produces modulations of the frequency of ferromagnetic resonance and the linewidth of the resonance spectra. The observed parabolic dependences are well explained by the damping-like and field-like components of spin transfer torque.

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Dynamical Spin Injection Based on Heating Effect due to Ferromagnetic Resonance

Kazuto Yamanoi, Yuki Yokotani, Takashi Kimura

Physical Review Applied （AMER PHYSICAL SOC）  8 （ 5 ）  2017年11月

研究論文（学術雑誌）, 共著, 筆頭著者, 査読有り,  ISSN  2331-7019

　概要を見る

Dynamical spin injection based on the ferromagnetic resonance is an attractive and powerful method for generating and manipulating the spin current. To date, in a ferromagnet/nonmagnet bilayer system, the spin-pumping effect from the ferromagnet into the nonmagnet has been considered only as the mechanism of the dynamical spin injection. Here, we examine another method for the dynamical spin injection based on the heating effect due to the ferromagnetic resonance in a (Co,Fe)B/Pt bilayer system. The (Co,Fe)B film heated by the ferromagnetic resonance produces the temperature gradient across the (Co,Fe)B/Pt interface, resulting in the thermal spin injection from the (Co,Fe)B layer into the Pt film. The obtained electrical signal clearly shows the spin Hall signature and exceeds 20 mV Ω-1 m-1, which is relatively large compared to the values reported in similar bilayer structures driven by spin pumping. The structural dependence of the inverse spin Hall signal and its power dependence provide consistent results with the dynamical thermal-spin-injection model due to the ferromagnetic resonance.

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Stability of standing spin wave in permalloy thin film studied by anisotropic magnetoresistance effect

K. Yamanoi, Y. Yokotani, X. Cui, S. Yakata, T. Kimura

Journal of Applied Physics （AIP Publishing）  118 （ 23 ） 233909 - 233909 2015年12月

研究論文（学術雑誌）, 共著, 筆頭著者, 査読有り,  ISSN  0021-8979

　概要を見る

We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of the standing spin wave is an important advantage for the high power operation of the spin-wave device.

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Saturation of attenuation length of spin waves in thick permalloy films

Masaki Ota, Kazuto Yamanoi, Shinya Kasai, Seiji Mitani, Takashi Manago

Japanese Journal of Applied Physics （IOP PUBLISHING LTD）  54 （ 11 ）  2015年11月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  0021-4922

　概要を見る

The permalloy (Py) thickness dependence of the magnetostatic spin wave (MSSW) propagation was investigated. Large-group velocity is realized for thick Py films and the MSSW can propagate more than 150 μm. However, attenuation length hardly changes for samples with a Py thickness of more than 100 nm, despite the increasing group velocity with increasing thickness. The eddy current effect decreases the wave channel thickness and it could cause the damping enhancement due to intralayer spin pumping in thick Py films.

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Heat dissipation due to ferromagnetic resonance in a ferromagnetic metal monitored by electrical resistance measurement

Kazuto Yamanoi, Yuki Yokotani, Takashi Kimura

Applied Physics Letters （AMER INST PHYSICS）  107 （ 18 ） 182410 - 182410 2015年11月

研究論文（学術雑誌）, 共著, 筆頭著者, 査読有り,  ISSN  0003-6951

　概要を見る

The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated.

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