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Shiomi, Yuki*; Nomura, Kentaro*; Kajiwara, Yosuke*; Eto, Kazuma*; Novak, M.*; Segawa, Koji*; Ando, Yoichi*; Saito, Eiji
Physical Review Letters, 113(19), p.196601_1 - 196601_5, 2014/11
Times Cited Count：308 Percentile：98.94(Physics, Multidisciplinary)Uchida, Kenichi*; Adachi, Hiroto; Kajiwara, Yosuke*; Maekawa, Sadamichi; Saito, Eiji
Solid State Physics, 64; Recent Advances in Magnetic Insulators; From Spintronics to Microwave Applications, p.1 - 27, 2013/11
Times Cited Count：14 Percentile：17.43(Physics, Condensed Matter)Qiu, Z.*; Ando, Kazuya*; Uchida, Kenichi*; Kajiwara, Yosuke*; Takahashi, Ryo*; Nakayama, Hiroyasu*; An, Toshu*; Fujikawa, Yasunori*; Saito, Eiji
Applied Physics Letters, 103(9), p.092404_1 - 092404_4, 2013/08
Times Cited Count：131 Percentile：95.78(Physics, Applied)A platinum (Pt)/yttrium iron garnet (YIG) bilayer system with a well-controlled interface has been developed; spin mixing conductance at the Pt/YIG interface has been studied. A clear interface with good crystal perfection is experimentally demonstrated to be one of the important factors for an ultimate spin mixing conductance. The spin mixing conductance is obtained to be 1.3
10
m
at the well-controlled Pt/YIG interface, which is close to a theoretical prediction.
Fe
O
Kajiwara, Yosuke*; Uchida, Kenichi*; Kikuchi, Daisuke*; An, Toshu*; Fujikawa, Yasunori*; Saito, Eiji
Applied Physics Letters, 103(5), p.052404_1 - 052404_4, 2013/07
Times Cited Count：7 Percentile：28.54(Physics, Applied)Heat-current-induced manipulation of spin relaxation in YFeO under an in-plane temperature gradient is investigated. We show that the linewidth of the ferromagnetic resonance spectrum, i.e., the spin relaxation, in an YFeO film increases or decreases depending on the temperature-gradient direction and that this modulation is attributed to the spin-transfer torque caused by a thermally induced transverse spin-wave spin current in the YFeO film. The experimental results also show that the spin-current magnitude generated by spin pumping in an attached Pt film is inversely proportional to the square of the modulated Gilbert damping constant, consistent with a phenomenological spin-pumping model.
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
Times Cited Count：144 Percentile：96.41(Chemistry, Physical)Uchida, Kenichi*; Nonaka, Tatsumi*; Kikkawa, Takashi*; Kajiwara, Yosuke*; Saito, Eiji
Physical Review B, 87(10), p.104412_1 - 104412_6, 2013/03
Times Cited Count：110 Percentile：94.65(Materials Science, Multidisciplinary)The longitudinal spin Seebeck effect (LSSE) is investigated in various garnet ferritesY
Fe
O ( = Gd, Ca; = Al, Mn, V, In, Zr) by means of the inverse spin Hall effect in Pt films. The magnitude of the LSSE voltage in the Pt/YFeO samples is found to be enhanced with increasing concentration of Fe in the garnet ferrites, which can be explained by a change in the spin-mixing conductance at the Pt/YFeO interfaces. We also investigate the dependence of the LSSE voltage on macroscopic magnetic parameters of YFeO. The experimental results show that the LSSE voltage in the Pt/YFeO samples hasa positive correlation with the Curie temperature and the saturation magnetization, but no clear correlation with the gyromagnetic ratio and the Gilbert damping constant of the samples.
Jungfleisch, M. B.*; An, Toshu*; Ando, Kazuya*; Kajiwara, Yosuke*; Uchida, Kenichi*; Vasyuchka, V. I.*; Chumak, A. V.*; Serga, A. A.*; Saito, Eiji; Hillebrands, B.*
Applied Physics Letters, 102(6), p.062417_1 - 062417_4, 2013/02
Times Cited Count：49 Percentile：84.11(Physics, Applied)Kirihara, Akihiro*; Uchida, Kenichi*; Kajiwara, Yosuke*; Ishida, Masahiko*; Nakamura, Yasunobu*; Manako, Takashi*; Saito, Eiji; Yorozu, Shinichi*
Nature Materials, 11(8), p.686 - 689, 2012/08
Times Cited Count：257 Percentile：98.48(Chemistry, Physical)Hou, D.*; Qiu, Z.*; Harii, Kazuya; Kajiwara, Yosuke*; Uchida, Kenichi*; Fujikawa, Yasunori*; Nakayama, Hiroyasu*; Yoshino, Tatsuro*; An, Toshu*; Ando, Kazuya*; et al.
Applied Physics Letters, 101(4), p.042403_1 - 042403_4, 2012/07
Times Cited Count：82 Percentile：91.88(Physics, Applied)Inverse spin Hall effect has been investigated in bismuth(Bi)/permalloy(Py) bilayer films by using the spin pumping at room temperature. From the ferromagnetic-resonance-spectrum linewidth data, Bi is proved to be a good spin sink in our structure. We measured inverse spin Hall voltage and conductance of the Bi/Py bilayer and found that the inverse spin Hall current, 
, decreases with increasing the Bi thickness, which is in contrast to the former understanding in similar bilayer systems, e.g., Pt/Py. We constructed a model to explain the thickness dependence of quantitatively, in which spin transport modulation near Bi/Py interface is considered.
Uchida, Kenichi*; Ota, Takeru*; Adachi, Hiroto; Xiao, J.*; Nonaka, Tatsumi*; Kajiwara, Yosuke*; Bauer, G. E. W.*; Maekawa, Sadamichi; Saito, Eiji
Journal of Applied Physics, 111(10), p.103903_1 - 103903_11, 2012/05
Times Cited Count：132 Percentile：95.87(Physics, Applied)
Fe
/Pt filmsNakayama, Hiroyasu*; Ando, Kazuya*; Harii, Kazuya; Yoshino, Tatsuro*; Takahashi, Ryo*; Kajiwara, Yosuke*; Uchida, Kenichi*; Fujikawa, Yasunori*; Saito, Eiji
Physical Review B, 85(14), p.144408_1 - 144408_7, 2012/04
Times Cited Count：217 Percentile：98.06(Materials Science, Multidisciplinary)Geometric effects on the inverse spin Hall effect (ISHE) induced by the spin pumping driven by the ferromagnetic resonance (FMR) have been investigated quantitatively. We measured the FMR spectra and the electromotive force induced by the ISHE with changing the size and the thickness in NiFe/Pt films. The intensity of generated charge currents due to the ISHE changes systematically with changing the film geometry. The experimental results show a clear difference between NiFe and Pt thickness dependence of the ISHE induced by the spin pumping.
Qiu, Z.*; Kajiwara, Yosuke*; Ando, Kazuya*; Fujikawa, Yasunori*; Uchida, Kenichi*; Tashiro, Takaharu*; Harii, Kazuya*; Yoshino, Tatsuro*; Saito, Eiji
Applied Physics Letters, 100(2), p.022402_1 - 022402_3, 2012/01
Times Cited Count：32 Percentile：74.10(Physics, Applied)In a simple all-oxide system, spin pumping driven by spin wave resonances have been investigated by using the inverse spin-Hall effect (ISHE). In a lanthanum doped yttrium iron garnet (La:YIG)/indium tin oxide (ITO) bilayer film, the spin pumping generates and injects a spin current into the ITO layer, and an electromotive force signal is observed via the ISHE. The electromotive forces were measured depend on the out-of-plane magnetic-field-angle and the microwave excitation power, which were consistent with the theoretical prediction of the ISHE. The realization of the all-oxide spin pumping system extends possibilities for the oxide spintronics.
Fe
O/Pt hybrid structureUchida, Kenichi*; An, Toshu*; Kajiwara, Yosuke*; Toda, Masaya*; Saito, Eiji
Applied Physics Letters, 99(21), p.212501_1 - 212501_3, 2011/11
Times Cited Count：51 Percentile：84.31(Physics, Applied)A spin current generated from a surface acoustic wave (SAW) was observed in an YFeO/Pt(YIG)/Pt hybrid structure. At the YIG/Pt interface, a SAW generated in the YIG layer was found to pump a spin current into the Pt layer, which was detected through the inverse spin-Hall effect in the Pt. The YIG/Pt lateral structure combined with a piezoelectric wedge transducer enables the systematic investigation of the spin-voltage distribution due to the SAW in the YIG. Since the observed phenomenon has high affinity with SAW-based electronics, it will pave the way for constructing spintronic SAW devices.
Kajiwara, Yosuke*; Takahashi, Saburo*; Maekawa, Sadamichi; Saito, Eiji*
IEEE Transactions on Magnetics, 47(6), p.1591 - 1594, 2011/06
Times Cited Count：9 Percentile：45.71(Engineering, Electrical & Electronic)Ando, Kazuya*; Takahashi, Saburo; Ieda, Junichi; Kajiwara, Yosuke*; Nakayama, Hiroyasu*; Yoshino, Tatsuro*; Harii, Kazuya*; Fujikawa, Yasunori*; Matsuo, Mamoru*; Maekawa, Sadamichi; et al.
Journal of Applied Physics, 109(10), p.103913_1 - 103913_11, 2011/05
Times Cited Count：489 Percentile：99.53(Physics, Applied)The inverse spin-Hall effect (ISHE) induced by the spin pumping has been investigated systematically in simple ferromagnetic/paramagnetic bilayer systems. The spin pumping driven by ferromagnetic resonance injects a spin current into the paramagnetic layer, which gives rise to an electromotive force transverse to the spin current using the ISHE in the paramagnetic layer. In a NiFe/Pt film, we found an electromotive force perpendicular to the applied magnetic field at the ferromagnetic resonance condition. The spectral shape of the electromotive force is well reproduced using a simple Lorentz function, indicating that the electromotive force is due entirely to the ISHE induced by the spin pumping; the extrinsic magnetogalvanic effects are eliminated in this measurement. The electromotive force varies systematically by changing the microwave power, magnetic-field angle, and film size, which are well reproduced by a calculation based on the Landau-Lifshitz-Gilbert equation combined with the models of the ISHE and spin pumping. The electromotive force was observed also in a Pt/YFe
GaO film, in which the metallic NiFe layer is replaced by an insulating YFeGaO layer, supporting that the spin-pumping-induced ISHE is responsible for the observed electromotive force.
Sandweg, C. W.*; Kajiwara, Yosuke*; Chumak, A. V.*; Serga, A. A.*; Vasyuchka, V. I.*; Jungfleisch, M. B.*; Saito, Eiji; Hillebrands, B.*
Physical Review Letters, 106(21), p.216601_1 - 216601_4, 2011/05
Times Cited Count：271 Percentile：98.31(Physics, Multidisciplinary)Yoshino, Tatsuro*; Ando, Kazuya*; Harii, Kazuya*; Nakayama, Hiroyasu*; Kajiwara, Yosuke*; Saito, Eiji
Applied Physics Letters, 98(3), p.132503_1 - 132503_3, 2011/03
Times Cited Count：34 Percentile：75.74(Physics, Applied)We show a clear guideline for generating a large spin current using the spin pumping in metallic bilayer films. We measured spin currents generated by the spin pumping in Ni
Fe/Pt bilayer films using the inverse spin-Hall effect (ISHE). The magnitude of the ISHE signals are well reproduced by a calculation based on the model of the spin pumping. The result shows that the amplitude of a spin current is universally determined by the product of the saturation magnetization, the additional damping constant, and the solid angle of the magnetization precession.
Fe/Pt filmsNakayama, Hiroyasu*; Ando, Kazuya*; Harii, Kazuya*; Fujikawa, Yasunori*; Kajiwara, Yosuke*; Yoshino, Tatsuro*; Saito, Eiji
Journal of Physics; Conference Series, 266, p.012100_1 - 012100_4, 2011/01
Times Cited Count：9 Percentile：95.62(Materials Science, Multidisciplinary)The inverse spin-Hall effect, conversion of spin currents into electric voltage, has been investigated in NiFe/Pt bilayer films with different length and width. We measured the electric voltage generated by the inverse spin-Hall effect induced by the spin pumping at room temperature. The experimental results indicate that the electric voltage induced by the inverse spin-Hall effect is proportional to the length of NiFe/Pt bilayer films. In contrast, the electric voltage exhibits almost no variation by changing the width of the NiFe/Pt films. These results are consistent with the inverse spin-Hall effect model.
/Pt ( = Ni, Fe, and NiFe) bilayer filmYoshino, Tatsuro*; Ando, Kazuya*; Harii, Kazuya*; Nakayama, Hiroyasu*; Kajiwara, Yosuke*; Saito, Eiji
Journal of Physics; Conference Series, 266, p.012115_1 - 012115_4, 2011/01
Times Cited Count：12 Percentile：97.32(Materials Science, Multidisciplinary)The spin-mixing conductances in /Pt ( = Ni, Fe, and NiFe) bilayer films were quantified from the peak-to-peak linewidth of ferromagnetic resonance (FMR) spectra based on the model of the spin pumping. When the Pt layer is attached to the layer, we found the enhancement of the FMR linewidth due to the spin pumping. The experimental results show that the spin-mixing conductances in /Pt ( = Ni, Fe, and NiFe) bilayer films have the same order of magnitude, showing that spin injection efficiency in the spin pumping is almost identical in these films.
Uchida, Kenichi*; Xiao, J.*; Adachi, Hiroto; Oe, Junichiro; Takahashi, Saburo; Ieda, Junichi; Ota, Takeru*; Kajiwara, Yosuke*; Umezawa, Hiromitsu*; Kawai, Hirotaka*; et al.
Nature Materials, 9(11), p.894 - 897, 2010/11
Times Cited Count：1146 Percentile：99.88(Chemistry, Physical)Thermoelectric generation is an essential function in future energy-saving technologies. However, it has so far been an exclusive feature of electric conductors, a situation which limits its application; conduction electrons are often problematic in the thermal design of devices. Here we report electric voltage generation from heat flowing in an insulator. We reveal that, despite the absence of conduction electrons, the magnetic insulator LaY
FeO can convert a heat flow into a spin voltage. Attached Pt films can then transform this spin voltage into an electric voltage as a result of the inverse spin Hall effect. The experimental result require us to introduce a thermally activated interface spin exchange between LaYFeO and Pt. Our findings extend the range of potential materials for thermoelectric applications and provide a crucial piece of information for understanding the physics of the spin Seebeck effect.
