Irradiation test using foreign reactor, 1; Study of irradiation test with capsule temperature control system (Joint research)

Takabe, Yugo; Otsuka, Noriaki; Fuyushima, Takumi; Sayato, Natsuki; Inoue, Shuichi; Morita, Hisashi; Jaroszewicz, J.*; Migdal, M.*; Onuma, Yuichi; Tobita, Masahiro*; et al.

JAEA-Technology 2022-040, 45 Pages, 2023/03

JAEA-Technology-2022-040.pdf:6.61MB

Because of the decommission of the Japan Materials Testing Reactor (JMTR), the domestic neutron irradiation facility, which had played a central role in the development of innovative nuclear reactors and the development of technologies to further improve the safety, reliability, and efficiency of light water reactors, was lost. Therefore, it has become difficult to pass on the operation techniques of the irradiation test reactors and irradiation technologies, and to train human resources. In order to cope with these issues, we conducted a study on the implementation of irradiation tests using overseas reactors as neutron irradiation sites as an alternative method. Based on the "Arrangement between the National Centre for Nuclear Research and the Japan Atomic Energy Agency for Cooperation in Research and Development on Testing Reactor," the feasibility of conducting an irradiation test at the MARIA reactor (30 MW) owned by the National Centre for Nuclear Research (NCBJ) using the temperature control system, which is one of the JMTR irradiation technologies, was examined. As a result, it was found that the irradiation test was possible by modifying the ready-made capsule manufactured in accordance with the design and manufacturing standards of the JMTR. After the modification, a penetration test, an insulation continuity test, and an operation test in the range of room temperature to 300C, which is the operating temperature of the capsule, were conducted and favorable results were obtained. We have completed the preparations prior to transport to the MARIA reactor.

Direct and alternating magnon spin currents across a junction interface irradiated by linearly polarized laser

Nakata, Koki; Onuma, Yuichi*

Physical Review B, 105(14), p.144436_1 - 144436_7, 2022/04

https://doi.org/10.1103/PhysRevB.105.144436

Using a junction of the ferromagnetic insulators irradiated by linearly polarized laser, we propose a method for the generation of dc and ac spin currents of magnons across the junction interface, and provide an analytical formula for magnon transport induced by the inversion symmetry breaking.

Microscopic theory of spin Hall magnetoresistance

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

Physical Review B, 102(9), p.094437_1 - 094437_10, 2020/09

https://doi.org/10.1103/PhysRevB.102.094437

Universal -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

AA2019-0205.pdf:0.36MB

https://doi.org/10.1103/PhysRevB.100.014406

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.

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

AA2019-0013.pdf:0.42MB

https://doi.org/10.1103/PhysRevB.99.134403

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.

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

https://www.furukawa.co.jp/rd/review/fj138/fj138_02.pdf

no abstracts in English

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

https://doi.org/10.1063/1.5041464

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

https://doi.org/10.1103/PhysRevLett.120.037201

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.

Theory of the spin Peltier effect

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

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

https://doi.org/10.1103/PhysRevB.96.134412

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.

Spin transport in half-metallic ferromagnets

Onuma, Yuichi; Matsuo, Mamoru; Maekawa, Sadamichi

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

https://doi.org/10.1103/PhysRevB.94.184405

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 , with being temperature and is sensitive to . We propose that spin Hall conductivity may be a tool to study the minority-spin state.