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Journal Articles

Sodium-cooled Fast Reactors

Ohshima, Hiroyuki; Morishita, Masaki*; Aizawa, Kosuke; Ando, Masanori; Ashida, Takashi; Chikazawa, Yoshitaka; Doda, Norihiro; Enuma, Yasuhiro; Ezure, Toshiki; Fukano, Yoshitaka; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

This book is a collection of the past experience of design, construction, and operation of two reactors, the latest knowledge and technology for SFR designs, and the future prospects of SFR development in Japan. It is intended to provide the perspective and the relevant knowledge to enable readers to become more familiar with SFR technology.

Journal Articles

Temporal change in radiological environments on land after the Fukushima Daiichi Nuclear Power Plant accident

Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Sato, Tetsuro*; Seki, Akiyuki; Sanada, Yukihisa; Wainwright-Murakami, Haruko*; et al.

Journal of Radiation Protection and Research, 44(4), p.128 - 148, 2019/12

Journal Articles

Spin pumping blocked by single-layer graphene

Haku, Satoshi*; Tashiro, Takaharu*; Nakayama, Hiroyasu*; Ieda, Junichi; Entani, Shiro; Sakai, Seiji; Ando, Kazuya*

Applied Physics Express, 8(7), p.073009_1 - 073009_3, 2015/07

 Times Cited Count:5 Percentile:18.73(Physics, Applied)

We found that the spin pumping in a Ni$$_{81}$$Fe$$_{19}$$/Pt bilayer is strongly suppressed by inserting single-layer graphene (SLG) at the interface. The spin pumping in the Ni$$_{81}$$Fe$$_{19}$$/Pt bilayer enhances the magnetization damping of the ferromagnetic layer, which is quantified from microwave frequency dependence of ferromagnetic resonance linewidth. We show that the enhancement of the magnetization damping due to the spin pumping disappears in a Ni$$_{81}$$Fe$$_{19}$$/SLG/Pt trilayer. This result indicates that the spin pumping is blocked by the atomic monolayer, demonstrating the crucial role of the interfacial short-range spin-exchange coupling in the spin pumping in metallic systems.

Journal Articles

Polaron spin current transport in organic semiconductors

Watanabe, Shun*; Ando, Kazuya*; Kang, K.*; Mooser, S.*; Vaynzof, Y.*; Kurebayashi, Hidekazu*; Saito, Eiji; Sirringhaus, H.*

Nature Physics, 10(4), p.308 - 313, 2014/04

 Times Cited Count:164 Percentile:97.87(Physics, Multidisciplinary)

Journal Articles

Spin mixing conductance at a well-controlled platinum/yttrium iron garnet interface

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:112 Percentile:95.88(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$$times$$10$$^{18}$$m$$^{-2}$$ at the well-controlled Pt/YIG interface, which is close to a theoretical prediction.

Journal Articles

Solution-processed organic spin-charge converter

Ando, Kazuya*; Watanabe, Shun*; Mooser, S.*; Saito, Eiji; Sirringhaus, H.*

Nature Materials, 12(7), p.622 - 627, 2013/07

 Times Cited Count:152 Percentile:97.27(Chemistry, Physical)

We show that a pure spin current can be produced in a solution-processed conducting polymer by pumping spins through a ferromagnetic resonance in an adjacent magnetic insulator, and that this generates an electric voltage across the polymer film. We demonstrate that the experimental characteristics of the generated voltage are consistent with it being generated through an inverse spin Hall effect in the conducting polymer. In contrast with inorganic materials, the conducting polymer exhibits coexistence of high spin-current to charge-current conversion efficiency and long spin lifetimes. Our discovery opens a route for a new generation of molecular-structure-engineered spintronic devices, which could lead to important advances in plastic spintronics.

JAEA Reports

The International Atomic Energy Agency Nuclear Energy Management School 2012

Ohgama, Kazuya; Ando, Yoko; Yamaguchi, Mika; Ikuta, Yuko; Shinohara, Nobuo; Murakami, Hiroyuki; Yamashita, Kiyonobu; Uesaka, Mitsuru*; Demachi, Kazuyuki*; Komiyama, Ryoichi*; et al.

JAEA-Review 2013-004, 76 Pages, 2013/05

JAEA-Review-2013-004.pdf:13.53MB

JAEA together with the Japan Nuclear Human Resource Development Network (JN-HRD Net), the University of Tokyo (UT) and the Japan Atomic Industrial Forum (JAIF) cohosted the IAEA-Nuclear Energy Management School in Tokai Village, aiming that Japan will be the center of nuclear HRD in the Asian region. In the school, not only lectures by IAEA experts, but also lectures by Japanese experts and technical visits were included for foreign participants. The school contributed to the internationalization of Japanese young professionals, development of nuclear human resource of other countries, and enhancement of cooperation between IAEA and Japan. Additionally, collaborative relationship within JN-HRD Net was strengthened by the school. In this report, findings obtained during the preparatory work and the school period are reported for future international nuclear HRD activities in Japan.

Journal Articles

Spin-pump-induced spin transport in $$p$$-type Si at room temperature

Shiko, Eiji*; Ando, Kazuya*; Kubo, Kazuki*; Saito, Eiji; Shinjo, Teruya*; Shiraishi, Seiji*

Physical Review Letters, 110(12), p.127201_1 - 127201_5, 2013/03

 Times Cited Count:148 Percentile:97.36(Physics, Multidisciplinary)

A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in $$p$$-type silicon ($$p$$-Si). Ferromagnetic resonance and effective s-d coupling in Ni$$_{80}$$Fe$$_{20}$$ results in spin accumulation at the Ni$$_{80}$$Fe$$_{20}$$/$$p$$-Si interface, inducing spin injection and the generation of spin current in the $$p$$-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the $$p$$-Si. This approach demonstrates the generation and transport of pure spin current in $$p$$-Si at room temperature.

Journal Articles

Heat-induced damping modification in yttrium iron garnet/platinum hetero-structures

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:47 Percentile:85.88(Physics, Applied)

Journal Articles

Spin pumping by nonreciprocal spin waves under local excitation

Iguchi, Ryo*; Ando, Kazuya*; Qiu, Z.*; An, Toshu*; Saito, Eiji; Sato, Tetsuya*

Applied Physics Letters, 102(2), p.022406_1 - 022406_3, 2013/01

 Times Cited Count:17 Percentile:58.33(Physics, Applied)

We measured spatial distribution of spin pumping by nonreciprocal magnetostatic surface waves (MSSWs) using inverse spin Hall effect (ISHE) in a YIG/Pt system under local excitation. The local intensity of spin pumping by MSSWs shows center displacement of $$pm$$ 1 mm from the center of a waveguide according to the reversal of a bias field, which is due to the nonreciprocal propagation of MSSWs over a macroscopic distance. The combination of spin pumping and ISHE enables electrical investigation of local spin dynamics in a magnetic insulator.

Journal Articles

Directional control of spin-wave emission by spatially shaped light

Sato, Takuya*; Terui, Yuki*; Moriya, Rai*; Ivanov, B. A.*; Ando, Kazuya*; Saito, Eiji; Shimura, Tsutomu*; Kuroda, Kazuo*

Nature Photonics, 6(10), p.662 - 666, 2012/10

 Times Cited Count:191 Percentile:99.15(Optics)

In future spintronics it is anticipated that spin waves will function as unique information carriers that are free from Joule heating. Directional control of spin-wave emission has been desired for the realization of switching devices. Here, we propose a promising technique that makes use of a spatially shaped light pulse with circular polarization. Focusing this light pulse on a magnet generates spin waves via the inverse Faraday effect. Moreover, the wave number distribution of the spin waves is determined by the spatial intensity distribution of the light spot. We demonstrate the principle of this technique both theoretically and experimentally. We successfully control the direction of the energy flow by shaping the light spot into an ellipse, with its major axis parallel or perpendicular to the magnetic field.

Journal Articles

Interface induced inverse spin Hall effect in bismuth/permalloy bilayer

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:73 Percentile:92.24(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, $$I_c$$, 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 $$I_c$$ quantitatively, in which spin transport modulation near Bi/Py interface is considered.

Journal Articles

Spin pumping driven by bistable exchange spin waves

Ando, Kazuya*; Saito, Eiji

Physical Review Letters, 109(2), p.026602_1 - 026602_5, 2012/07

 Times Cited Count:47 Percentile:85.86(Physics, Multidisciplinary)

Spin pumping driven by bistable exchange spin waves is demonstrated in a Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ film under parametric excitation. In the Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ film, the spin pumping driven by parametric excitation selectively enhances the relaxation of short-wavelength exchange spin waves, indicating strong coupling between the exchange spin waves and spin currents at the interface through efficient spin transfer. The parametric spin pumping, furthermore, allows direct access to nonlinear spin wave dynamics in combination with the inverse spin Hall effect, revealing unconventional bistability of the exchange spin waves.

Journal Articles

Geometry dependence on inverse spin Hall effect induced by spin pumping in Ni$$_{81}$$Fe$$_{19}$$/Pt films

Nakayama, 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:186 Percentile:98.01(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 Ni$$_{81}$$Fe$$_{19}$$/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 Ni$$_{81}$$Fe$$_{19}$$ and Pt thickness dependence of the ISHE induced by the spin pumping.

Journal Articles

All-oxide system for 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:31 Percentile:75.67(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.

Journal Articles

Observation of the inverse spin Hall effect in silicon

Ando, Kazuya*; Saito, Eiji

Nature Communications (Internet), 3, p.629_1 - 629_6, 2012/01

 Times Cited Count:188 Percentile:97.87(Multidisciplinary Sciences)

Journal Articles

Electrically tunable spin injector free from the impedance mismatch problem

Ando, Kazuya*; Takahashi, Saburo; Ieda, Junichi; Kurebayashi, Hidekazu*; Trypiniotis, T.*; Barnes, C. H. W.*; Maekawa, Sadamichi; Saito, Eiji

Nature Materials, 10(9), p.655 - 659, 2011/09

 Times Cited Count:246 Percentile:98.67(Chemistry, Physical)

Journal Articles

Inverse spin-Hall effect induced by spin pumping in metallic systems

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:405 Percentile:99.49(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 Ni$$_{81}$$Fe$$_{19}$$/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/Y$$_3$$Fe$$_4$$GaO$$_{12}$$ film, in which the metallic Ni$$_{81}$$Fe$$_{19}$$ layer is replaced by an insulating Y$$_3$$Fe$$_4$$GaO$$_{12}$$ layer, supporting that the spin-pumping-induced ISHE is responsible for the observed electromotive force.

Journal Articles

Spin pumping efficiency from half metallic Co$$_2$$MnSi

Chudo, Hiroyuki; Ando, Kazuya*; Saito, Kesami*; Okayasu, Satoru; Haruki, Rie; Sakuraba, Yuya*; Yasuoka, Hiroshi; Takanashi, Koki; Saito, Eiji

Journal of Applied Physics, 109(7), p.073915_1 - 073915_4, 2011/04

 Times Cited Count:19 Percentile:61.42(Physics, Applied)

We present spin pumping using a Heusler alloy Co$$_2$$MnSi/Pt bilayer film. A spin current is produced by a ferromagnetic resonance (FMR) technique. The pure spin current injected into the Pt layer from the Co$$_2$$MnSi layer is detected by the inverse spin-Hall effect (ISHE), which converts the spin current into an electric current. We estimated a damping constant of the Co$$_2$$MnSi/Pt bilayer film from an angular dependence of FMR spectra. Using the damping constant efficiency of spin pumping from the Co$$_2$$MnSi layer is evaluated. We found that a mixing conductance at the Co$$_2$$MnSi/Pt interface is comparable to that at a permalloy/Pt interface.

Journal Articles

Universality of the spin pumping in metallic bilayer films

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:31 Percentile:77.1(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$$_{1-x}$$Fe$$_{x}$$/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.

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