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Journal Articles

Vortex rectenna powered by environmental fluctuations

Lustikova, J.*; Shiomi, Yuki*; Yokoi, Naoto*; Kabeya, Noriyuki*; Kimura, Noriaki*; Ienaga, Koichiro*; Kaneko, Shinichi*; Okuma, Satoshi*; Takahashi, Saburo*; Saito, Eiji

Nature Communications (Internet), 9, p.4922_1 - 4922_6, 2018/11

 Times Cited Count:13 Percentile:78.13(Multidisciplinary Sciences)

Journal Articles

Enhanced magneto-optical Kerr effect at Fe/insulator interfaces

Gu, B.; Takahashi, Saburo*; Maekawa, Sadamichi

Physical Review B, 96(21), p.214423_1 - 214423_6, 2017/12

 Times Cited Count:6 Percentile:41.1(Materials Science, Multidisciplinary)

Journal Articles

Generation of megahertz-band spin currents using nonlinear spin pumping

Watanabe, Shingo*; Hirobe, Daichi*; Shiomi, Yuki*; Iguchi, Ryo*; Daimon, Shunsuke*; Kameda, Mai*; Takahashi, Saburo*; Saito, Eiji

Scientific Reports (Internet), 7, p.4576_1 - 4576_6, 2017/07

 Times Cited Count:4 Percentile:28.18(Multidisciplinary Sciences)

Journal Articles

Optically transparent ferromagnetic nanogranular films with tunable transmittance

Kobayashi, Nobukiyo*; Masumoto, Hiroshi*; Takahashi, Saburo*; Maekawa, Sadamichi

Scientific Reports (Internet), 6, p.34227_1 - 34227_7, 2016/09

 Times Cited Count:24 Percentile:77.22(Multidisciplinary Sciences)

Journal Articles

Theory of spin Hall magnetoresistance (SMR) and related phenomena

Chen, Y.-T.*; Takahashi, Saburo*; Nakayama, Hiroyasu*; Althammer, M.*; Goennenwein, S. T. B.*; Saito, Eiji; Bauer, G. E. W.*

Journal of Physics; Condensed Matter, 28(10), p.103004_1 - 103004_15, 2016/03

 Times Cited Count:57 Percentile:63.7(Physics, Condensed Matter)

We review the so-called spin Hall magnetoresistance (SMR) in bilayers of a magnetic insulator and a metal, in which spin currents are generated in the normal metal by the spin Hall effect. The associated angular momentum transfer to the ferromagnetic layer and thereby the electrical resistance is modulated by the angle between the applied current and the magnetization direction. The SMR provides a convenient tool to non-invasively measure the magnetization direction and spin-transfer torque to an insulator. We introduce the minimal theoretical instruments to calculate the SMR, i.e. spin diffusion theory and quantum mechanical boundary conditions. This leads to a small set of parameters that can be fitted to experiments. We discuss the limitations of the theory as well as alternative mechanisms such as the ferromagnetic proximity effect and Rashba spin-orbit torques, and point out new developments.

Journal Articles

Spin hydrodynamic generation

Takahashi, Ryo*; Matsuo, Mamoru; Ono, Masao; Harii, Kazuya; Chudo, Hiroyuki; Okayasu, Satoru; Ieda, Junichi; Takahashi, Saburo*; Maekawa, Sadamichi; Saito, Eiji

Nature Physics, 12, p.52 - 56, 2016/01

 Times Cited Count:65 Percentile:95.17(Physics, Multidisciplinary)

Journal Articles

Giant dielectric and magnetoelectric responses in insulating nanogranular films at room temperature

Kobayashi, Nobukiyo*; Masumoto, Hiroshi*; Takahashi, Saburo*; Maekawa, Sadamichi

Nature Communications (Internet), 5, p.4417_1 - 4417_6, 2014/07

 Times Cited Count:40 Percentile:86.19(Multidisciplinary Sciences)

The electric and magnetic properties of matter are of great interest for materials science and their use in electronic applications. Large dielectric and magnetoelectric responses of materials at room temperature are a great advantage for electromagnetic device applications. Here we present a study of FeCo-MgF nanogranular films exhibiting giant dielectric and magnetoelectric responses at room temperature; with dielectric constant $$varepsilon$$'=490 and magnetoelectric response $$Delta$$$$varepsilon$$'/$$varepsilon$$'$$_{0}$$=3%. In these films, Fe-Co alloy-based nanometer-sized magnetic granules are dispersed in a Mg-fluoride-based insulator matrix. Insulating nanogranular films are a new class of multifunctional materials. The giant responses are caused by spin-dependent charge oscillation between magnetic granules via quantum-mechanical tunnelling. A possible application of such insulating nanogranular materials with giant response is in the construction of a tunable device, in which impedance components such as capacitance and inductance are tunable at room temperature.

Journal Articles

Anomalous temperature dependence of current-induced torques in CoFeB/MgO heterostructures with Ta-based underlayers

Kim, J.*; Sinha, J.*; Mitani, Seiji*; Hayashi, Masamitsu*; Takahashi, Saburo*; Maekawa, Sadamichi; Yamanouchi, Michihiko*; Ono, Hideo*

Physical Review B, 89(17), p.174424_1 - 174424_8, 2014/05

 Times Cited Count:81 Percentile:94.83(Materials Science, Multidisciplinary)

We have studied the underlayer thickness and temperature dependencies of the current-induced effective field in CoFeB/MgO heterostructures with Ta-based underlayers. The underlayer thickness at which the effective field saturates is found to be different between the two orthogonal components of the effective field; i.e., the dampinglike term tends to saturate at a smaller underlayer thickness than the fieldlike term. For large underlayer thickness films in which the effective field saturates, we find that the measurement temperature significantly influences the size of the effective field. A striking difference is found in the temperature dependence of the two components: the dampinglike term decreases whereas the fieldlike term increases with increasing temperature. Using a simple spin diffusion-spin transfer model, we find that all of these results can be accounted for provided the real and imaginary parts of an effective spin mixing conductance are negative. These results imply that either spin transport in this system is different from conventional metallic interfaces or effects other than spin diffusion into the magnetic layer need to be taken into account in order to model the system accurately.

Journal Articles

Effect of anisotropic spin absorption on the Hanle effect in lateral spin valves

Izuchi, Hiroshi*; Fukuma, Yasuhiro*; Takahashi, Saburo*; Maekawa, Sadamichi; Otani, Yoshichika*

Physical Review B, 89(8), p.081308_1 - 081308_5, 2014/02

 Times Cited Count:25 Percentile:76.27(Materials Science, Multidisciplinary)

Journal Articles

Theory of spin Hall magnetoresistance

Chen, Y.-T.*; Takahashi, Saburo*; Nakayama, Hiroyasu*; Althammer, M.*; Goennenwein, S. T. B.*; Saito, Eiji; Bauer, G. E. W.*

Physical Review B, 87(14), p.144411_1 - 144411_9, 2013/04

 Times Cited Count:468 Percentile:99.66(Materials Science, Multidisciplinary)

We present a theory of the spin Hall magnetoresistance (SMR) in multilayers made from an insulating ferromagnet F, such as yttrium iron garnet (YIG), and a normal metal N with spin-orbit interactions, such as platinum (Pt). The SMR is induced by the simultaneous action of spin Hall and inverse spin Hall effects and therefore a nonequilibrium proximity phenomenon. We compute the SMR in F|N and F|N|F layered systems, treating N by spin-diffusion theory with quantum mechanical boundary conditions at the interfaces in terms of the spin-mixing conductance. Our results explain the experimentally observed spin Hall magnetoresistance in N|F bilayers. For F|N|F spin valves we predict an enhanced SMR amplitude when magnetizations are collinear. The SMR and the spin-transfer torques in these trilayers can be controlled by the magnetic configuration.

Journal Articles

Spin Hall effect

Maekawa, Sadamichi; Takahashi, Saburo

Spin Current (2nd Edition), p.194 - 208, 2012/10

Journal Articles

Spin Hall effect in superconductors

Takahashi, Saburo*; Maekawa, Sadamichi

Japanese Journal of Applied Physics, 51(1), p.010110_1 - 010110_7, 2012/01

 Times Cited Count:19 Percentile:65.55(Physics, Applied)

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:220 Percentile:98.75(Chemistry, Physical)

Journal Articles

Composite excitation of Josephson phase and spin waves in Josephson junctions with ferromagnetic insulator

Hikino, Shinichi*; Mori, Michiyasu; Takahashi, Saburo; Maekawa, Sadamichi

Journal of the Physical Society of Japan, 80(7), p.074707_1 - 074707_8, 2011/07

 Times Cited Count:7 Percentile:50.11(Physics, Multidisciplinary)

Journal Articles

Giant enhancement of spin accumulation and long-distance spin precession in metallic lateral spin valves

Fukuma, Yasuhiro*; Le, W.*; Izuchi, Hiroshi*; Takahashi, Saburo; Maekawa, Sadamichi; Otani, Yoshichika*

Nature Materials, 10(7), p.527 - 531, 2011/07

 Times Cited Count:150 Percentile:97.64(Chemistry, Physical)

Journal Articles

Detection of spin-wave spin current in a magnetic insulator

Kajiwara, Yosuke*; Takahashi, Saburo*; Maekawa, Sadamichi; Saito, Eiji*

IEEE Transactions on Magnetics, 47(6), p.1591 - 1594, 2011/06

 Times Cited Count:8 Percentile:47.07(Engineering, Electrical & Electronic)

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:338 Percentile:99.43(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 transfer torque in MTJs with synthetic ferrimagnetic layers by the Keldysh approach

Ichimura, Masahiko*; Hamada, Tomoyuki*; Imamura, Hiroshi*; Takahashi, Saburo*; Maekawa, Sadamichi

Journal of Applied Physics, 109(7), p.07C906_1 - 07C906_3, 2011/03

 Times Cited Count:4 Percentile:20.9(Physics, Applied)

Journal Articles

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

 Times Cited Count:43 Percentile:85.67(Materials Science, Multidisciplinary)

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.

Journal Articles

Linear-response theory of spin Seebeck effect in ferromagnetic insulators

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

Physical Review B, 83(9), p.094410_1 - 094410_6, 2011/03

 Times Cited Count:204 Percentile:98.59(Materials Science, Multidisciplinary)

We formulate a linear response theory of the spin Seebeck effect, i.e., a spin voltage generation from heat current flowing in a ferromagnet. Our approach focuses on the collective magnetic excitation of spins, i.e., magnons. We show that the linear-response formulation provides us with a qualitative as well as quantitative understanding of the spin Seebeck effect observed in a prototypical magnet, yttrium iron garnet.

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