Intrinsic surface magnetic anisotropy in YFeO as the origin of low-magnetic-field behavior of the spin Seebeck effect

Uchida, Kenichi*; Oe, Junichiro*; Kikkawa, Takashi*; Daimon, Shunsuke*; Hou, D.*; Qiu, Z.*; Saito, Eiji

Physical Review B, 92(1), p.014415_1 - 014415_8, 2015/07

https://doi.org/10.1103/PhysRevB.92.014415

Unidirectional spin-wave heat conveyer

An, Toshu*; Vasyuchka, V. I.*; Uchida, Kenichi*; Chumak, A. V.*; Yamaguchi, Kazuya*; Harii, Kazuya; Oe, Junichiro*; Jungfleisch, M. B.*; Kajiwara, Yosuke*; Adachi, Hiroto; et al.

Nature Materials, 12(6), p.549 - 553, 2013/06

https://doi.org/10.1038/nmat3628

Time-domain observation of the spinmotive force in permalloy nanowires

Hayashi, Masamitsu*; Ieda, Junichi; Yamane, Yuta; Oe, Junichiro*; Takahashi, Yukiko*; Mitani, Seiji*; Maekawa, Sadamichi

Physical Review Letters, 108(14), p.147202_1 - 147202_5, 2012/04

https://doi.org/10.1103/PhysRevLett.108.147202

Spinmotive force associated with a moving domain wall is observed directly in permalloy nanowires using real time voltage measurements with proper subtraction of the electromotive force. Whereas the wall velocity exhibits nonlinear dependence on a magnetic field, the generated voltage increases linearly with the field. We show that the sign of the voltage reverses when the wall propagation direction is altered. Numerical simulations explain quantitatively these features of spinmotive force and indicate that the spinmotive force scales with the field even in a field range where the wall motion is no longer associated with periodic structure transformation.

Spinmotive force due to intrinsic energy of ferromagnetic nanowires

Yamane, Yuta; Ieda, Junichi; Oe, Junichiro*; Barnes, S. E.*; Maekawa, Sadamichi

Applied Physics Express, 4(9), p.093003_1 - 093003_3, 2011/09

https://doi.org/10.1143/APEX.4.093003

Numerical study on the spin Seebeck effect

Oe, Junichiro; Adachi, Hiroto; Takahashi, Saburo; Maekawa, Sadamichi

Physical Review B, 83(11), p.115118_1 - 115118_5, 2011/03

https://doi.org/10.1103/PhysRevB.83.115118

Thermally driven spin-wave spin currents in ferromagnetic (FM) materials and a resulting measurable electric signal in a normal metal (NM) probe placed on FM are theoretically investigated. We develop the numerical technique for calculating a spin Seebeck signal detected by the NM probe that converts the spin current to the charge current. By taking into account the fluctuation-dissipation theorem for thermally fluctuating spins at the interface of a FM/NM junction, the spin current is induced in the NM probe via an exchange interaction when the FM feels the temperature gradient. Numerical simulation clarifies the role of the sample boundary on the spatial distribution of the spin current both in FM and NM. The spin-wave spin current that flows parallel to the heat current is also investigated.

Gigantic enhancement of spin Seebeck effect by phonon drag

Adachi, Hiroto; Uchida, Kenichi*; Saito, Eiji; Oe, Junichiro; Takahashi, Saburo; Maekawa, Sadamichi

Applied Physics Letters, 97(25), p.252506_1 - 252506_3, 2010/12

https://doi.org/10.1063/1.3529944

We investigate both theoretically and experimentally a gigantic enhancement of the spin Seebeck effect in a prototypical magnet LaYFeO at low temperatures. Our theoretical analysis sheds light on the important role of phonons: the spin Seebeck effect is enormously enhanced by nonequilibrium phonons that drag low-lying spin excitations. We further argue that this scenario gives a clue to understand the observation of the spin Seebeck effect that is unaccompanied by a global spin current, and predict that the substrate condition affects the observed signal.

New numerical approach for studying diluted magnetic semiconductors

Oe, Junichiro; Gu, B.; Maekawa, Sadamichi

Kotai Butsuri, 45(5), p.269 - 278, 2010/06

http://ci.nii.ac.jp/naid/40017190872

We report a new combined numerical approach for studying diluted magnetic semiconductors (DMS). In this approach, realistic parameters obtained by the calculation are used for performing quantum Monte Carlo calculations. We show that the proposed approach well describes the magnetic properties of DMS and can be used for designing the new DMS materials which has high Curie temperatures.

Spin-wave-mediated spin Seebeck effect

Adachi, Hiroto; Oe, Junichiro; Takahashi, Saburo; Maekawa, Sadamichi

no journal, , 

It has been a conventional wisdom that a spin current is carried by conduction electrons in metals. However, it was recently demonstrated that there exist another type of spin current carried by low-lying excitations of localized spins, i.e., the spin-wave excitations. One of the important feature of the latter spin current, which we call here a spin-wave spin current, is that it can propagate over a distance as long as several millimeters. Moreover, a recent report on the spin Seebeck effect in an insulating magnet provide us with a good opportunity to discuss the scenario of spin-wave-mediated spin Seebeck effect. In this talk, we focus on the spin Seebeck effect observed in an insulating magnet of yttrium iron garnet, and discuss the scenario of spin-wave-mediated spin Seebeck effect.

Numerical study on the thermal spin transport in ferromagnetic insulators

Adachi, Hiroto; Takahashi, Saburo; Maekawa, Sadamichi; Oe, Junichiro

no journal, , 

We report the theoretical study on the thermal spin transport in ferromagnetic insulators. By using the fluctuation-dissipation theorem, we derive a random torque acting on the magnetic moment at the finite temperature. The numerical results shows the propagating spin wave that is driven by the thermal gradient. Furthermore, we argue a measurable voltage induced by the inverse spin Hall effect by using realistic parameters of actual setup.

Numerical study on the thermally driven spin-wave spin current

Oe, Junichiro; Adachi, Hiroto; Takahashi, Saburo; Maekawa, Sadamichi

no journal, , 

Recently, the relation between the heat current and the spin current has much attracted from the view of the spintronics applications. The heat current induces the spin current, the spin Seebeck effect, has been discovered not only inferromagnetic metals but also in ferromagnetic semiconductors and ferromagnetic insulators. In this reports, we investigate the spin Seebeck effect by using the numerical simulation. We focus on the dynamics of the magnetization in the presence of the fluctuating torque which represents finite temperatures. The spin current is driven by the magnetization dynamics and converted to the charge current in a normal metal probe. We use the Landau-Lifshitz-Gilbert equation for calculating the magnetization dynamics and the diffusion equation for the dynamics of the conduction electrons. Our results show good agreement with the experimental results qualitatively.