Magnetic evolution, phase transitions, and electronic band structure of the ferrotoroidic candidate BaCrS

Zhao, G.*; Li, J.*; Zhang, J.*; 小嶋 健児*; Cai, Y.*; 伊藤 孝; Yoon, S. W.*; Wang, X.*; 前川 禎通*; Su, G.*; et al.

Physical Review Research (Internet), 8(1), p.013331_1 - 013331_10, 2026/03

https://doi.org/10.1103/h576-nnnz

Ferrotoroidic materials, which break both time- and space-reversal symmetries to enhance magnetoelectric responses, are of great interest for applications. BaCrS, a recently synthesized quasi-one-dimensional ferrotoroidic candidate, combines polarization, magnetization, and toroidal moment, yet its electronic band structure, magnetic evolution, and phase transitions remain incompletely understood to date. Here, we investigate BaCrS, using electrical transport, direct current magnetization, alternating current susceptibility, specific heat, and muon spin rotation (SR) measurements, along with various first-principles calculations. Electrical transport measurements and density functional theory confirm a narrow band gap (0.707~eV, experimentally; 0.680~eV, theoretically). SR measurements reveal that static magnetism dominates down to 2~K, with an ordered volume fraction of 89% at this temperature. Two distinct transitions are identified: one around the Nel temperature [~K] and another corresponding to a phase transition near 30~K, as consistently indicated by our complementary experimental techniques. The absence of dynamic critical behaviors and the lack of a -type specific heat anomaly are consistent with a first-order-like transition at . Based on various complementary experimental results and theoretical calculations, we propose a hypothesis that the 30~K broad feature arises from the complex interplay between crystal structure distortion and magnetic coupling, which is potentially directly linked to ferrotoroidicity. As the first study integrating SR with complementary experiments and first-principles calculations to explore ferrotoroidicity, this work provides key insights into the underlying physics of BaCrS and related compounds in this area.

原子力科学研究所放射性廃棄物処理場の新規制基準対応; 第3廃棄物処理棟、解体分別保管棟及び減容処理棟の耐震補強

池谷 正太郎; 鈴木 武; 横堀 智彦; 菅原 聡; 横田 顕; 菊地 絃太; 村口 佳典; 北原 理; 瀬谷 真南人; 黒澤 剛史; et al.

JAEA-Technology 2025-001, 169 Pages, 2025/08

JAEA-Technology-2025-001.pdf:14.22MB

原子力科学研究所の放射性廃棄物処理場は、多様な施設により構成されており、その中に、第3廃棄物処理棟、解体分別保管棟及び減容処理棟がある。これらの3建家は、核原料物質、核燃料物質及び原子炉の規制に関する法律による規制を受けており、耐震重要度分類でCクラスに分類されている。東京電力福島第一原子力発電所の事故を契機として原子力規制委員会が策定した新規制基準に対応するため、最新の建築基準法に基づき3建家の耐震評価を実施したところ、許容応力度評価で一部基準を満足しない箇所が認められた。これに対応すべく、令和3年3月5日に設計及び工事の計画の認可(設工認)を取得し、令和3年(2021)から令和4年(2022)までの期間にて耐震補強を行った。本報告書は、第3廃棄物処理棟、解体分別保管棟及び減容処理棟の各建家の耐震設計の概況をはじめ、耐震改修工事の工事概要、作業体制、安全管理、使用前事業者検査について取りまとめたものである。

Magnetism of kagome metals (FeCo)Sn studied by SR

Cai, Y.*; Yoon, S.*; Sheng, Q.*; Zhao, G.*; Seewald, E. F.*; Ghosh, S.*; Ingham, J.*; Pasupathy, A. N.*; Queiroz, R.*; Lei, H.*; et al.

Physical Review B, 111(21), p.214412_1 - 214412_17, 2025/06

https://doi.org/10.1103/PhysRevB.111.214412

We study the magnetic properties of the metallic kagome system (FeCo)Sn by a combination of muon spin relaxation (SR), magnetic susceptibility, and scanning tunneling microscopy (STM) measurements in single crystal specimens with Co concentrations = 0, 0.11, 0.8. In the undoped antiferromagnetic compound FeSn, we find possible signatures for a previously unidentified phase that sets in at ~K, well beneath the Neel temperature ~K as indicated by a peak in the relaxation rate 1/ observed in zero field (ZF) and longitudinal field (LF) SR measurements, with a corresponding anomaly in the ac and dc susceptibility, and an increase in the static width 1/ in ZF-SR measurements. No signatures of spatial symmetry breaking are found in STM down to 7~K. Related to the location and motion of muons in FeSn, we confirmed a previous report that about 40% of the implanted muons reside at a field-cancelling high symmetry site at ~K, while an onset of thermal hopping changes the site occupancy at higher temperatures. In FeCoSn, where disorder eliminated the field-cancellation effect, all the implanted muons exhibit precession and/or relaxation in the ordered state. In FeCoSn, we find canonical spin glass behavior with freezing temperature ~K; the ZF and LF-SR time spectra exhibit results similar to those observed in dilute alloy spin glasses CuMn and AuFe, with a critical behavior of at and as . The absence of spin dynamics at low temperatures makes a clear contrast to the spin dynamics observed by SR in many geometrically frustrated spin systems on insulating kagome, pyrochlore, and triangular lattices. The spin glass behavior of CoSn doped with dilute Fe moments is shown to originate primarily from the randomness of doped Fe moments rather than due to geometrical frustration of the underlying lattice.

Fukushima Daiichi Nuclear Power Plant accident analysis considering the thermal stratification and containment leakage

中村 勇気*; 小島 良洋*; 山下 拓哉; 下村 健太; 溝上 伸也

Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NUTHOS-14) (Internet), 12 Pages, 2024/08

At the Fukushima Daiichi Nuclear Power Plant accident, it has been reported that several units of containment vessel had failed, and large quantity of radionuclides had been released into the environment. However, the detailed accident progression of such a containment failure, which includes core melt, reactor vessel failure and following containment vessel behavior, has still large uncertainties. Especially for the unit 2 and 3, they had succeeded in the initial core cooling, but at last lost their cooling system and fell into severe accident to release the fission product into the environment. Nowadays, several information has been obtained by the internal inspection into the containment of the Fukushima Daiichi Nuclear Power Plants. To clarify the uncertainties in the accident scenario, considering the information and several insights already accustomed by previous research, the latest accident scenario in unit 2 and unit 3 of the Fukushima Daiichi Nuclear Power Plants accident are suggested and tested by the severe accident analysis code, MAAP in this study. It is shown that unit 2 and 3 both accident scenario would have resulted in the thermal stratification in suppression pool which encouraged the containment pressure response in the early phase of the accident. In addition, containment vessel leakage would have occurred and affected the containment depressurization.

Neutron transmission CB-KID imager using samples placed at room temperature

石田 武和*; Vu, TheDang*; 宍戸 寛明*; 相澤 一也; 奥 隆之; 及川 健一; 原田 正英; 小嶋 健児*; 宮嶋 茂之*; 小山 富男*; et al.

Journal of Low Temperature Physics, 214(3-4), p.152 - 157, 2024/02

https://doi.org/10.1007/s10909-023-03030-9

We built a new cryostat to apply a current-biased kinetic inductance detector (CB-KID) for conducting neutron transmission imaging of room temperature samples under pulsed neutrons. A Wood's metal alloy of melting temperature 75.2C was placed at room temperature to inspect the measurement system at J-PARC. Since one of the four phases of Wood's metal is a fine Cd-rich needle phase (width 25 m and length 5 mm), it is suitable for observing fine mosaic structure selectively by neutron imaging. The spatial resolution of the CB-KID imager was estimated as 10 m by using a Gd Siemens-star pattern. The CB-KID system is useful to conduct transmission imaging for various materials rather easily at room temperature.

Orientation mapping of YbSn single crystals based on Bragg-dip analysis using a delay-line superconducting sensor

宍戸 寛明*; Vu, TheDang*; 相澤 一也; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 奥 隆之; 曽山 和彦; 宮嶋 茂之*; et al.

Journal of Applied Crystallography, 56(4), p.1108 - 1113, 2023/08

https://doi.org/10.1107/S1600576723005204

Recent progress in high-power pulsed neutron sources has stimulated the development of the Bragg dip and Bragg edge analysis methods using a two-dimensional neutron detector with high temporal resolution to resolve the neutron energy by the time-of-flight method. A delay-line current-biased kinetic inductance detector (CB-KID) is a two-dimensional superconducting sensor with a high temporal resolution and multi-hit capability. Here, it is demonstrated that a delay-line CB-KID with a B neutron conversion layer can be applied to high-spatial-resolution neutron transmission imaging and spectroscopy up to 100 eV. Dip structures are observed in the transmission spectra of YbSn single crystals, induced by Bragg diffraction and nuclear resonance absorption. The orientation mapping of YbSn crystals is successfully drawn based on the analysis of observed Bragg dip positions in the transmission spectra.

Magnons and spinons in BaCoTeO; A Composite system of isolated spin- triangular Heisenberg-like and frustrated honeycomb Ising-like antiferromagnets

児島 佑樹*; 栗田 伸之*; 田中 秀数*; 中島 健次

Physical Review B, 105(2), p.L020408_1 - L020408_6, 2022/01

https://doi.org/10.1103/PhysRevB.105.L020408

二次元性の良いスピン1/2Heisenberg三角格子反強磁性体を含むBaCoTeOの磁気励起を中性子散乱を用いて観測した。BaCoTeOの磁気モデルは2つの独立した二次元系スピン1/2Heisenberg三角格子反強磁性体とIsing的J1-J2-J3ハニカム格子反強磁性体で捉えることができる。三角格子に由来する励起スペクトルは線形スピン波理論の分散関係とは異なり、複数のロトンライクミニマムを持つ。これはフェルミオニックスピノンを用いた計算によって示される結果と類似している。ハニカム格子に由来する分散関係は高エネルギー領域に現われ、線形スピン波理論で捉えることができた。

Hybridization of Bogoliubov quasiparticles between adjacent CuO layers in the triple-layer cuprate BiSrCaCuO studied by angle-resolved photoemission spectroscopy

出田 真一郎*; Johnston, S.*; 吉田 鉄平*; 田中 清尚*; 森 道康; 安齋 太陽*; 井野 明洋*; 有田 将司*; 生天目 博文*; 谷口 雅樹*; et al.

Physical Review Letters, 127(21), p.217004_1 - 217004_6, 2021/11

https://doi.org/10.1103/PhysRevLett.127.217004

Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO layers in the triple-layer cuprate high-temperature superconductor BiSrCaCuO is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anti-crossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the -wave superconducting gap of both BQP bands smoothly develops with momentum without abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off-nodal to the anti-nodal region, which is explained by the momentum-dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs, as well as the combination of phonon modes of the triple CuO layers and spin fluctuations are discussed.

Neutron imaging for intermetallic alloy using a delay line current-biased kinetic-inductance detector

宍戸 寛明*; Vu, TheDang*; 相澤 一也; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 奥 隆之; 曽山 和彦; 宮嶋 茂之*; et al.

Journal of Physics; Conference Series, 1975, p.012023_1 - 012023_8, 2021/07

https://doi.org/10.1088/1742-6596/1975/1/012023

The current-biased kinetic-inductance detector (CB-KID) is a solid-state superconducting neutron detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrate high temperature operation of CB-KID at 7.9 K with the delayline method. High temperature operation reduces imaging pixel size by suppressing signal propagation velocity. High spatial neutron transmission image for a mixed metal alloy consisting of heavy elements Sm and Sn is successfully constructed. We also examine the capability of element discrimination imaging based on the resonance dip analysis.

Homogeneity of neutron transmission imaging over a large sensitive area with a four-channel superconducting detector

Vu, TheDang; 宍戸 寛明*; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 宮嶋 茂之*; 奥 隆之; 曽山 和彦; 相澤 一也; et al.

Superconductor Science and Technology, 34(1), p.015010_1 - 015010_10, 2021/01

https://doi.org/10.1088/1361-6668/abc2af

We demonstrated that a four-readout superconducting neutron imaging system shows good spatial heterogeneity and linearity using the delay-line method. We examined the precise pattern of a B-dot-array absorber and found the X-direction pitch (Px) = 250.7 um with a scatter of (Hx)= 5.4 um and the Y-direction pitch (Py)= 249.1 um with a scatter of (Hy)= 3.4 um while the B dot array was fully extended toward the X direction across the detector sensitive area. We consider that this demonstrates detection with good spatial homogeneity and conclude. The transmission-imaging system is suitable for use at pulsed neutron facilities. We also reported a clear transmission image of tiny screws and nuts, and ladybug (insect). We recognize that further efforts to improve the detection efficiency are necessary to make using the detector more practical.