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Journal Articles

Giant spin hydrodynamic generation in laminar flow

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:0 Percentile:100(Multidisciplinary Sciences)

Journal Articles

Universal $$frac{1}{3}$$-suppression of magnonic shot noise in diffusive insulating magnets

Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*

Physical Review B, 100(1), p.014406_1 - 014406_8, 2019/07

 Times Cited Count:0 Percentile:100(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.

Journal Articles

Angular momentum compensation manipulation to room temperature of the ferrimagnet Ho$$_{3-x}$$Dy$$_{x}$$Fe$$_5$$O$$_{12}$$ detected by the Barnett effect

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:7 Percentile:21.51(Physics, Applied)

Journal Articles

Asymmetric quantum shot noise in magnon transport

Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*

Physical Review B, 99(13), p.134403_1 - 134403_7, 2019/04

 Times Cited Count:2 Percentile:56.85(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.

JAEA Reports

Setting of EAL in JMTR

Kawamata, Takanori; Onuma, Yuichi; Hanakawa, Hiroki

JAEA-Review 2018-031, 33 Pages, 2019/02

JAEA-Review-2018-031.pdf:1.62MB

As "Regulations on events to be reported by nuclear disaster prevention manager based on act on special measures concerning nuclear emergency preparedness" was revised and enfored in 2017, Nuclear operator emergency action plan at Oarai Research and Development Institute was reconsidered, and Emergency Action Level (EAL) in JMTR was newly set. In setting the EAL, characteristics of the JMTR and EAL in nuclear power reactors were considerd because the characteristics of research reactors are different in reactor types. This report shows the basic policy and the selection result of the EAL setting in the JMTR.

Journal Articles

Advanced analysis technology for new material and product development

Sasaki, Hirokazu*; Nishikubo, Hideo*; Nishida, Shinsuke*; Yamazaki, Satoshi*; Nakasaki, Ryusuke*; Isomatsu, Takemi*; Minato, Ryuichiro*; Kinugawa, Kohei*; Imamura, Akihiro*; Otomo, Shinya*; et al.

Furukawa Denko Jiho, (138), p.2 - 10, 2019/02

no abstracts in English

Journal Articles

Magnonic noise and Wiedemann-Franz law

Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*

Physical Review B, 98(9), p.094430_1 - 094430_8, 2018/09

 Times Cited Count:8 Percentile:32.09(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.

Journal Articles

Observation of gyromagnetic reversal

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:9 Percentile:36.37(Physics, Applied)

Journal Articles

Dirac surface state-modulated spin dynamics in a ferrimagnetic insulator at room temperature

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:8 Percentile:26.78(Multidisciplinary Sciences)

Journal Articles

Spin current noise of the spin Seebeck effect and spin pumping

Matsuo, Mamoru*; Onuma, Yuichi; Kato, Takeo*; Maekawa, Sadamichi

Physical Review Letters, 120(3), p.037201_1 - 037201_5, 2018/01

 Times Cited Count:19 Percentile:9.11(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.

Journal Articles

Heat and spin interconversion

Onuma, Yuichi; Matsuo, Mamoru*; Maekawa, Sadamichi; Saito, Eiji

Magune, 12(5), p.217 - 224, 2017/10

no abstracts in English

Journal Articles

Theory of the spin Peltier effect

Onuma, Yuichi; Matsuo, Mamoru*; Maekawa, Sadamichi

Physical Review B, 96(13), p.134412_1 - 134412_4, 2017/10

 Times Cited Count:21 Percentile:14.69(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.

Journal Articles

Theory of spin hydrodynamic generation

Matsuo, Mamoru*; Onuma, Yuichi; Maekawa, Sadamichi

Physical Review B, 96(2), p.020401_1 - 020401_5, 2017/07

 Times Cited Count:14 Percentile:25.88(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.

Journal Articles

Spin transport in half-metallic ferromagnets

Onuma, Yuichi; Matsuo, Mamoru; Maekawa, Sadamichi

Physical Review B, 94(18), p.184405_1 - 184405_5, 2016/11

 Times Cited Count:9 Percentile:43.52(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 $$T^{3/2}$$, with $$T$$ being temperature and is sensitive to $$T$$. We propose that spin Hall conductivity may be a tool to study the minority-spin state.

Journal Articles

Origin of the spin Seebeck effect in compensated ferrimagnets

Gepr$"a$gs, 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:80 Percentile:2.93(Multidisciplinary Sciences)

Journal Articles

Magnon instability driven by heat current in magnetic bilayers

Onuma, Yuichi*; Adachi, Hiroto; Saito, Eiji; Maekawa, Sadamichi

Physical Review B, 92(22), p.224404_1 - 224404_8, 2015/12

 Times Cited Count:7 Percentile:58.13(Materials Science, Multidisciplinary)

Journal Articles

Enhanced dc spin pumping into a fluctuating ferromagnet near Tc

Onuma, Yuichi*; Adachi, Hiroto; Saito, Eiji; Maekawa, Sadamichi

Physical Review B, 89(17), p.174417_1 - 174417_10, 2014/05

 Times Cited Count:61 Percentile:6.75(Materials Science, Multidisciplinary)

JAEA Reports

Simulator for materials testing reactors

Takemoto, Noriyuki; Sugaya, Naoto; Otsuka, Kaoru; Hanakawa, Hiroki; Onuma, Yuichi; Hosokawa, Jinsaku; Hori, Naohiko; Kaminaga, Masanori; Tamura, Kazuo*; Hotta, Koji*; et al.

JAEA-Technology 2013-013, 44 Pages, 2013/06

JAEA-Technology-2013-013.pdf:4.42MB

A real-time simulator for operating both a reactor and irradiation facilities of a materials testing reactor, Simulator of Materials Testing Reactors, was developed for understanding reactor behavior and upskilling in order to utilize for a nuclear human resource development and to promote partnership with developing countries which have a plan to introduce nuclear power plant. The simulator is designed based on the JMTR (Japan Materials Testing Reactor) and it simulates operation, irradiation tests and various kinds of anticipated operational transients and accident conditions caused by the reactor and irradiation facilities. The development of the simulator was sponsored by the Japanese government as one of the specialized projects of advanced research infrastructure in order to promote basic as well as applied researches. This report summarizes the simulation model, hardware specification and operation procedure of the simulator.

Journal Articles

Spin Seebeck effect in antiferromagnets and compensated ferrimagnets

Onuma, Yuichi; Adachi, Hiroto; Saito, Eiji; Maekawa, Sadamichi

Physical Review B, 87(1), p.014423_1 - 014423_7, 2013/01

 Times Cited Count:86 Percentile:4.03(Materials Science, Multidisciplinary)

JAEA Reports

Outline of new irradiation facility in JMTR

Takahashi, Kiyoshi; Hanawa, Hiroshi; Onuma, Yuichi; Hosokawa, Jinsaku; Kanno, Masaru

JAEA-Technology 2012-007, 31 Pages, 2012/03

JAEA-Technology-2012-007.pdf:4.76MB

The Japan Materials Testing Reactor (JMTR), achieving first criticality in March 1968, has been used in testing the durability and integrity of reactor fuels and components, basic nuclear research, the production of radioisotopes, and other purposes. The JMTR, however, stopped in August 2006 after its 165th operation cycle, and is currently under going partial renewal of reactor facilities and installation of new irradiation facilities, geared toward being restarted in 2012. Now, the installation of two new irradiation facilities under the LWR irradiation environment were finished until 2011FY. One is a power ramping test facility of high-burnup fuel. Another one is a material irradiation facility for IASCC research under the LWR irradiation environment. And another irradiation facility (Hydraulic rabbit irradiation facility) maintenance is carried out on 2011FY. This report is described the installed new irradiation facilities and established irradiation facility until 2011FY in JMTR.

46 (Records 1-20 displayed on this page)