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Nakata, Koki; Onuma, Yuichi*; Kim, S. K.*
Physical Review B, 105(18), p.184409_1 - 184409_7, 2022/05
Times Cited Count:2 Percentile:34.67(Materials Science, Multidisciplinary)We show that the ratio of the thermal to spin transport coefficient of magnons in insulating magnets exhibits a different behavior from the linear response and the universal law breaks down in the strong nonlinear regime.
Nakata, Koki; Onuma, Yuichi*
Physical Review B, 105(14), p.144436_1 - 144436_7, 2022/04
Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)Using a junction of the ferromagnetic insulators irradiated by linearly polarized laser, we propose a method for the generation of dc and ac spin currents of magnons across the junction interface, and provide an analytical formula for magnon transport induced by the inversion symmetry breaking.
Nakata, Koki; Onuma, Yuichi*
Physical Review B, 104(6), p.064408_1 - 064408_8, 2021/08
Times Cited Count:9 Percentile:62.1(Materials Science, Multidisciplinary)Using the quantum Boltzmann equation for Bose systems, we have developed the formula for thermal transport of bosons and found a difference from the conventional, with a particular focus on magnons.
Kato, Takeo*; Onuma, Yuichi*; Matsuo, Mamoru
Physical Review B, 102(9), p.094437_1 - 094437_10, 2020/09
Times Cited Count:16 Percentile:71.02(Materials Science, Multidisciplinary)Takahashi, Ryo*; Chudo, Hiroyuki; Matsuo, Mamoru; Harii, Kazuya*; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Nature Communications (Internet), 11, p.3009_1 - 3009_6, 2020/06
Times Cited Count:18 Percentile:80.01(Multidisciplinary Sciences)Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*
Physical Review B, 100(1), p.014406_1 - 014406_8, 2019/07
Times Cited Count:1 Percentile:4.76(Materials Science, Multidisciplinary)Extending a Boltzmann-Langevin theory to magnons, we show a universality of current-noise suppression in diffusive systems against the difference of quantum-statistical properties of bosons and fermions.
Imai, Masaki; Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Applied Physics Letters, 114(16), p.162402_1 - 162402_4, 2019/04
Times Cited Count:20 Percentile:73.01(Physics, Applied)Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*
Physical Review B, 99(13), p.134403_1 - 134403_7, 2019/04
Times Cited Count:4 Percentile:22(Materials Science, Multidisciplinary)We study a frequency-dependent noise-to-current ratio for asymmetric, symmetric, and noncommutative current noise in a ferromagnetic insulating junction, and extract quantum-mechanical properties of magnon transport at low temperatures. We demonstrate that the noncommutative noise, which vanishes in the dc limit (i.e., a classical regime), increases monotonically as a function of frequency, and show that the noncommutative noise associated directly with quantum fluctuations of magnon currents breaks through the classical upper limit determined by the symmetric noise and realizes asymmetric quantum shot noise. Finally, we show that our theoretical predictions are within experimental reach with current device and measurement schemes while exploiting low temperatures. Our work provides a platform toward experimental access to quantum fluctuations of magnon currents.
Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*
Physical Review B, 98(9), p.094430_1 - 094430_8, 2018/09
Times Cited Count:11 Percentile:49.2(Materials Science, Multidisciplinary)We theoretically establish mutual relations among magnetic momentum, heat, and fluctuations of propagating magnons in a ferromagnetic insulating junction in terms of noise and the bosonic Wiedemann-Franz (WF) law. Using the Schwinger-Keldysh formalism, we calculate all transport coefficients of a noise spectrum for both magnonic spin and heat currents, and establish Onsager relations between the thermomagnetic currents and the zero-frequency noise. Making use of the magnonic WF law and the Seebeck coefficient in the low-temperature limit, we theoretically discover universal relations, i.e. being independent of material parameters, for both the nonequilibrium and equilibrium noise, and show that each noise is described solely in terms of thermal conductance.
Imai, Masaki; Ogata, Yudai*; Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru*; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Applied Physics Letters, 113(5), p.052402_1 - 052402_3, 2018/07
Times Cited Count:18 Percentile:65.6(Physics, Applied)Tang, C.*; Song, Q.*; Chang, C.-Z.*; Xu, Y.*; Onuma, Yuichi; Matsuo, Mamoru*; Liu, Y.*; Yuan, W.*; Yao, Y.*; Moodera, J. S.*; et al.
Science Advances (Internet), 4(6), p.eaas8660_1 - eaas8660_6, 2018/06
Times Cited Count:30 Percentile:84.42(Multidisciplinary Sciences)Matsuo, Mamoru*; Onuma, Yuichi; Kato, Takeo*; Maekawa, Sadamichi
Physical Review Letters, 120(3), p.037201_1 - 037201_5, 2018/01
Times Cited Count:43 Percentile:89.44(Physics, Multidisciplinary)We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal metal (NM)/ferromagnet (FM) bilayer system. Starting with a simple FI-NM interface model with both spin-conserving and spin-non-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for an yttrium iron garnet (YIG) - platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the spin-non-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.
Onuma, Yuichi; Matsuo, Mamoru*; Maekawa, Sadamichi; Saito, Eiji
Magune, 12(5), p.217 - 224, 2017/10
no abstracts in English
Onuma, Yuichi; Matsuo, Mamoru*; Maekawa, Sadamichi
Physical Review B, 96(13), p.134412_1 - 134412_4, 2017/10
Times Cited Count:38 Percentile:83.36(Materials Science, Multidisciplinary)A microscopic theory of the spin Peltier effect in a bilayer structure comprising a paramagnetic metal (PM) and a ferromagnetic insulator (FI) based on the nonequilibrium Green's function method is presented. Spin current and heat current driven by temperature gradient and spin accumulation are formulated as functions of spin susceptibilities in the PM and the FI, and are summarized by Onsager's reciprocal relations. By using the current formulas, we estimate heat generation and absorption at the interface driven by the heat-current injection mediated by spins from PM into FI.
Matsuo, Mamoru*; Onuma, Yuichi; Maekawa, Sadamichi
Physical Review B, 96(2), p.020401_1 - 020401_5, 2017/07
Times Cited Count:42 Percentile:85.75(Materials Science, Multidisciplinary)Spin-current generation by fluid motion is theoretically investigated. Based on quantum kinetic theory, the spin-diffusion equation coupled with fluid vorticity is derived. We show that spin currents are generated by the vorticity gradient in both laminar and turbulent flows and that the generated spin currents can be detected by the inverse spin Hall voltage measurements, which are predicted to be proportional to the flow velocity in a laminar flow. In contrast, the voltage in a turbulent flow is proportional to the square of the flow velocity. This study will pave the way to fluid spintronics.
Onuma, Yuichi; Matsuo, Mamoru; Maekawa, Sadamichi
Physical Review B, 94(18), p.184405_1 - 184405_5, 2016/11
Times Cited Count:23 Percentile:67.71(Materials Science, Multidisciplinary)We theoretically investigate spin transport in half-metallic ferromagnets at finite temperatures. The side-jump and skew-scattering contributions to spin Hall conductivity are derived using the Kubo formula. The electron-magnon interaction causes a finite density of states in the energy gap of the minority-spin band and induces spin Hall conductivity. We show that spin Hall conductivity is proportional to , with being temperature and is sensitive to . We propose that spin Hall conductivity may be a tool to study the minority-spin state.
Geprgs, S.*; Kehlberger, A.*; Coletta, F.*; Qiu, Z.*; Guo, E.-J.*; Schulz, T.*; Mix, C.*; Meyer, S.*; Kamra, A.*; Althammer, M.*; et al.
Nature Communications (Internet), 7, p.10452_1 - 10452_6, 2016/02
Times Cited Count:152 Percentile:97.33(Multidisciplinary Sciences)Onuma, Yuichi*; Adachi, Hiroto; Saito, Eiji; Maekawa, Sadamichi
Physical Review B, 92(22), p.224404_1 - 224404_8, 2015/12
Times Cited Count:8 Percentile:35.57(Materials Science, Multidisciplinary)Onuma, Yuichi*; Adachi, Hiroto; Saito, Eiji; Maekawa, Sadamichi
Physical Review B, 89(17), p.174417_1 - 174417_10, 2014/05
Times Cited Count:101 Percentile:94.67(Materials Science, Multidisciplinary)Onuma, Yuichi; Adachi, Hiroto; Saito, Eiji; Maekawa, Sadamichi
Physical Review B, 87(1), p.014423_1 - 014423_7, 2013/01
Times Cited Count:117 Percentile:95.84(Materials Science, Multidisciplinary)