Cr doping-induced ferromagnetism in the spin-glass CdMnTe studied by X-ray magnetic circular dichroism

Verma, V.*; 坂本 祥哉*; 石川 弘一郎*; Singh, V. R.*; 石上 啓介*; 芝田 悟朗; 門野 利治*; 小出 常晴*; 黒田 真司*; 藤森 淳*

Physica B; Condensed Matter, 642, p.414129_1 - 414129_5, 2022/10

https://doi.org/10.1016/j.physb.2022.414129

The prototypical diluted magnetic semiconductor CdMnTe is a spin glass () or an antiferromagnet () but becomes ferromagnetic upon doping with a small amount of Cr atoms. To investigate the origin of the ferromagnetism in CdMnCrTe, we have studied its element specific magnetic properties by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). Measured XAS and XMCD spectra indicate that both Cr and Mn atoms are divalent and that the magnetic moments of Cr and Mn are aligned parallel. By analyzing the element-specific magnetization curves, we conclude that Cr doping leads to the formation of ferromagnetic or superparamagnetic clusters consisting of several Cr ions surrounded by a much larger number of Mn ions.

NMR studies on antiferromagnetic fluctuation in UPt

青山 泰介*; 小手川 恒*; 藤 秀樹*; 木村 憲彰*; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*

Physica B; Condensed Matter, 570, p.349 - 351, 2019/10

https://doi.org/10.1016/j.physb.2018.02.031

Pt-NMR measurements are performed on a heavy fermion superconductor UPt to investigate the in-plane anistropy. A splitting of the NMR line was observed and explained by anisotropic Knight shift tensors associated with the local symmetry of the Pt site.

Real time and real space analysis for coherent QENS and its application to liquid bismuth

菊地 龍弥*; 川北 至信

Physica B; Condensed Matter, 567, p.51 - 54, 2019/08

https://doi.org/10.1016/j.physb.2019.01.022

Real time and real space analysis for quasielastic neutron scattering (QENS) by means of the regularization method to estimate a spectrum has been developed. In our formalism, a mediation function between a dynamic structure factor, , and a time-space correlation function, ,is estimated to minimize the sum of the least square fitting term for in a space and the regularization term for in a space. On the application to liquid bismuth which shows complicate static local structure, it is shown that a distribution function for Gaussian superposition to represent has good characters as a mediating function. The calculated from the estimated mediation function showed a good agreement with the experimental even for small acoustic phonon excitation in a low region and gave more or less reasonable estimation of dynamic structure beyond the measured range. In addition of the main property of that the ability to focus onto the relaxation process at a specific atomic distance helped us to understand a complicated layered structure in liquid bismuth, possibility of easy separation of self-diffusion from coherent QENS is shown.

Status of neutron spectrometers at J-PARC

梶本 亮一; 横尾 哲也*; 中村 充孝; 川北 至信; 松浦 直人*; 遠藤 仁*; 瀬戸 秀紀*; 伊藤 晋一*; 中島 健次; 河村 聖子

Physica B; Condensed Matter, 562, p.148 - 154, 2019/06

BB2018-0526.pdf:2.45MB

https://doi.org/10.1016/j.physb.2018.11.061

Seven time-of-flight quasielastic/inelastic neutron scattering instruments are installed on six beamlines in the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC). Four of these instruments are chopper-type direct-geometry spectrometers, one is a near-backscattering indirect-geometry spectrometer, and the other two are spin-echo-type spectrometers. This paper reviews the characteristic features, recent scientific outcomes, and progress in development of MLF spectrometers.

Recent progress on practical materials study by Bragg edge imaging at J-PARC

及川 健一; Su, Y. H.; 鬼柳 亮嗣; 川崎 卓郎; 篠原 武尚; 甲斐 哲也; 廣井 孝介; Harjo, S.; Parker, J. D.*; 松本 吉弘*; et al.

Physica B; Condensed Matter, 551, p.436 - 442, 2018/12

https://doi.org/10.1016/j.physb.2017.12.038

We are promoting for practical product observation by the energy-resolved neutron imaging method using high-intensity pulsed neutrons at J-PARC, under the Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Bragg edge imaging, one of the energy-resolved neutron imaging methods for visualizing material properties, was applied to feasibility study of the temperature distribution of copper rod, complementary study of the texture and strain distribution of bent steel plates using neutron diffraction and EBSD, and so on. Outline of results obtained by these imaging experiments will be presented.

Study of the magnetization distribution in a grain-oriented magnetic steel using pulsed polarized neutron imaging

廣井 孝介; 篠原 武尚; 林田 洋寿*; Parker, J. D.*; Su, Y. H.; 及川 健一; 甲斐 哲也; 鬼柳 善明*

Physica B; Condensed Matter, 551, p.146 - 151, 2018/12

https://doi.org/10.1016/j.physb.2018.05.013

Grain oriented magnetic steel is widely used as a key material for magnetic industrial products. Since magnetic properties of steels are closely related to its magnetic domain structure, observation of the domain structure is important for understanding its magnetic properties. In this study, we attempted to observe the domain structure of a grain oriented steel using polarized pulsed neutron imaging. In the experiment, we first magnetized the sample by applying a magnetic field along the easy-to-magnetize direction via a coil, and confirmed the sample was magnetized almost uniformly from the obtained polarization distribution images. By analyzing the oscillatory behavior in the wavelength dependence of polarization, magnetization of the steel was estimated to be 1.82 T. Then, we removed the field and performed the same measurement. As a result, a striped domain structure was observed, with neighboring domains aligned anti-parallel to each other. From these results, it was demonstrated that our magnetic imaging method could visualize the magnetization and the direction of the domains in the practical steel.

Phonon dynamics of NaI investigated by G() analysis

中村 充孝; 菊地 龍弥*; 蒲沢 和也*; 川北 至信

Physica B; Condensed Matter, 551, p.351 - 354, 2018/12

BB2017-0467.pdf:0.48MB

https://doi.org/10.1016/j.physb.2017.12.057

実空間における動的構造関数G()は、非弾性中性子散乱実験により得られる動的構造因子S()から導出される。本研究では、典型的なアルカリハライド結晶であるNaIにG()解析を適用した。NaIは、構成元素の質量差が大きいために光学フォノンと音響フォノンのエネルギー差が大きくなるが、この特性はG()解析の妥当性を評価する上で有効である。J-PARCのフェルミチョッパー分光器四季で測定したNaI粉末のS()に対して、最大エントロピー法を利用した新開発の解析ソフトウェアを使ってG()に変換したところ、LAモードとTOモードが逆位相で振動することを見出した。この結果は物理的に妥当なものであり、G()解析の有用性を如実に示している。本発表ではさらなる解析結果について報告を行う予定である。

Characteristics of the 2012 model lithium-6 time-analyzer neutron detector (LiTA12) system as a high efficiency detector for resonance absorption imaging

甲斐 哲也; 佐藤 節夫*; 廣井 孝介; Su, Y. H.; 瀬川 麻里子; Parker, J. D.*; 松本 吉弘*; 林田 洋寿*; 篠原 武尚; 及川 健一; et al.

Physica B; Condensed Matter, 551, p.496 - 500, 2018/12

https://doi.org/10.1016/j.physb.2017.11.086

The 2012 model lithium-6 time-analyzer neutron detector (LiTA12) system, based on a lithium glass scintillator and multi-anode photomultiplier tube, has the highest neutron efficiency among the detectors for pulsed neutron imaging together with a flexibility of the efficiency by changing the thickness of the lithium glass. The authors expect this detector system could become a main detector system for the energy-resolved neutron imaging system, RADEN, at J-PARC, and have started evaluation of the LiTA12 system. For example, spatial resolution for resonance absorption imaging was evaluated by using a line-pair pattern made by 3 micro meter thick gold on a quartz plate. Less than 1 mm width line pairs were resolved at an 8 Mcps neutron counting rate and around 5 eV neutron energy.

Anomaly of structural relaxation in complex liquid metal of bismuth; Dynamic correlation function of coherent quasi-elastic neutron scattering

川北 至信; 菊地 龍弥*; 稲村 泰弘; 田原 周太*; 丸山 健二*; 花島 隆泰*; 中村 充孝; 鬼柳 亮嗣; 山内 康弘*; 千葉 薫*; et al.

Physica B; Condensed Matter, 551, p.291 - 296, 2018/12

https://doi.org/10.1016/j.physb.2017.12.037

単元素液体金属の中には、その静的構造が剛体球充填モデルでは全く表せない、複雑な構造を有する物質がある。液体ビスマスは、構造因子のメインピークの高波数側に非対称な肩構造を有する。二体分布関数の第一ピークと第二ピークの距離の比が1:2で、一次元的に配列しているような奇妙な値を示すとともに、第一ピークの長距離側に明確な肩構造を有する。二種類の直径の異なる剛体球からなるモデルでは、構造因子の肩構造が生じることから、こうした単元素液体金属の複雑性の起源として、短時間だけ生じる共有結合や、金属イオンを遮蔽する電子が有効二体間ポテンシャルに作り出す振動(フリーデル振動)など、まったく物理的描像が異なる仮説がいくつかなされている。そこで我々は液体ビスマスの中性子準弾性散乱を、J-PARCのMLFに設置された冷中性子ディスクチョッパー分光器を用いて測定し、液体ダイナミクスを動的相関関数から調べた。その結果、二体分布関数の第一ピークの肩構造の緩和時間が、第一ピークや第二ピークなどその他の主要構造に比べて著しく長いことが分かった。

Dynamical quadrupole structure factor of frustrated ferromagnetic chain

大西 弘明

Physica B; Condensed Matter, 536, p.346 - 349, 2018/05

https://doi.org/10.1016/j.physb.2017.10.056

In a spin-1/2 - Heisenberg chain with ferromagnetic and antiferromagnetic , the ground state in high magnetic fields is a quadrupole state, the so-called spin nematic state. To understand the properties of the spin nematic state from the viewpoint of excitation dynamics, we have studied dynamical spin structure factors by density-matrix renormalization group methods. In the spin nematic regime, we find gapless longitudinal and gapped transverse spin excitation spectra, in accordance with quasi-long-ranged longitudinal and short-ranged transverse spin correlations, respectively. These features can be examined by inelastic neutron scattering experiments. However, they are indirect evidence for the spin nematic state. Here, we proceed to analyze dynamical quadrupole structure factors to clarify excitation dynamics in the quadrupole channel. We observe gapless excitations at =, signaling quasi-long-ranged antiferro-quadrupole correlations. Information of spectral intensity distribution would be useful to discuss how we can detect the spin nematic state directly by experiments.