Electronic structure of the high- ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.035204

The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3 contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3 electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3 states have a finite contribution to the density of states at the Fermi energy. These states, presumably consisting of majority-spin - hybridized states or minority-spin e states, would be responsible for the ferromagnetic order in this material.

Origin of the dramatic change of fission mode in fermium isotopes investigated using Langevin equations

宮本 裕也*; 有友 嘉浩*; 田中 翔也; 廣瀬 健太郎; 西尾 勝久

Physical Review C, 99(5), p.051601_1 - 051601_7, 2019/05

https://doi.org/10.1103/PhysRevC.99.051601

The fission of even-even fermium nuclides Fm at low excitation energy was studied using Langevin equations of three-dimensional nuclear-shape parametrization. The mass distributions of fission fragments show a dramatic change from an asymmetric shape for the lighter fermium isotopes to sharp symmetric fission for the heavier isotopes. The time evolution of the nuclear shape on the potential surface reveals that the lighter fermium isotopes showing asymmetric fission are trapped in the second minimum for a substantial length of time before overcoming the second saddle point. This behavior changes dramatically for the compact symmetric fission found in the heavier neutron-rich fermium nuclei that disintegrate immediately after overcoming the first saddle point, without feeling the second barrier, resulting in a fission time two orders of magnitude shorter.

Cation distribution and magnetic properties in ultrathin (NiCo)FeO (x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism

若林 勇希*; 野中 洋亮*; 竹田 幸治; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; 芝田 悟朗*; 田中 新*; 斎藤 祐児; 山上 浩志; et al.

Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10

https://doi.org/10.1103/PhysRevMaterials.2.104416

We study the electronic structure and magnetic properties of epitaxial (NiCo)FeO(111) layers with thicknesses = 1.7 - 5.2 nm grown on AlO(111)/Si(111) structures. We revealed the crystallographic (octahedral or tetrahedral ) sites and the valences of the Fe, Co, and Ni cations using experimental soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra and configuration-interaction cluster-model calculation.

Role of multichance fission in the description of fission-fragment mass distributions at high energies

廣瀬 健太郎; 西尾 勝久; 田中 翔也*; Lguillon, R.*; 牧井 宏之; 西中 一朗*; Orlandi, R.; 塚田 和明; Smallcombe, J.*; Vermeulen, M. J.; et al.

Physical Review Letters, 119(22), p.222501_1 - 222501_6, 2017/12

https://doi.org/10.1103/PhysRevLett.119.222501

JAEAタンデム加速器施設で行ったO+U反応における多核子移行チャンネルを用いた実験により、U, Np、およびPuの核分裂質量分布を励起エネルギー1060MeVにおいて測定した。これらのうち、U, Npのデータは本実験により初めて観測された。原子核の殻効果の減衰によって対称分裂すると予想されていた高励起エネルギーにおいても、質量分布が非対称を示すことがわかった。搖動散逸定理に基づく動力学モデル計算との比較から、この振る舞いはマルチチャンス核分裂によるものであることを明らかにした。

Study of fission using multi-nucleon transfer reactions

西尾 勝久; 廣瀬 健太郎; Lguillon, R.*; 牧井 宏之; Orlandi, R.; 塚田 和明; Smallcombe, J.*; 千葉 敏*; 有友 嘉浩*; 田中 翔也*; et al.

Proceedings of 6th International Conference on Fission and Properties of Neutron-rich Nuclei (ICFN-6), p.590 - 597, 2017/11

https://doi.org/10.1142/9789813229426_0101

We are promoting a fission study using multi-nucleon transfer reactions, where excited states in neutron-rich actinide nuclei, which cannot be accessed by particle capture and/or fusion reactions, are populated. This allows us to study fission in the new region of chart of nuclei. Also, the excited states in the fissioning nucleus are widely populated in the reactions, thus the effects of excitation energy on fission can be investigated. Experiments were carried out at the JAEA tandem facility in Tokai, Japan. We studied reactions using the O beam (9MeV/u) and several actinide target nuclei such as Th, U, Np, Cm. Ejectile nuclei and thus the transfer channels were identified by a newly developed silicon E-E detectors. The produced nuclei in one experiment reached more than fifteen. Fission fragment mass distributions (FFMDs) were measured for each isotopes. Measured FFMDs are reproduced by a calculation based on the fluctuation-dissipation model (Langevin-type calculation), where effects of multi-chance fission were included. We also started to measure the prompt neutrons accompanied by fission.

Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

坂本 祥哉*; 若林 勇希*; 竹田 幸治; 藤森 伸一; 鈴木 博人*; 伴 芳祐*; 山上 浩志; 田中 雅明*; 大矢 忍*; 藤森 淳*

Physical Review B, 95(7), p.075203_1 - 075203_5, 2017/02

https://doi.org/10.1103/PhysRevB.95.075203

GeFe (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K and hence is a promising material for spintronic applications compatible with Si technology. We have studied its underlying electronic structure by soft X-ray angle-resolved photoemission spectroscopy measurements and first-principles supercell calculation. We observed finite Fe 3 components in the states at the Fermi level () in a wide region of momentum space, and the was located 0.35 eV above the valence-band maximum of the host Ge. Our calculation indicates that the is also within the deep acceptor-level impurity band induced by the strong -() hybridization. We conclude that the additional minority-spin electron characteristic of the Fe state is responsible for the short-range ferromagnetic coupling between Fe atoms.

Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor GeFe

若林 勇希*; 坂本 祥哉*; 竹田 幸治; 石上 啓介*; 高橋 文雄*; 斎藤 祐児; 山上 浩志; 藤森 淳*; 田中 雅明*; 大矢 忍*

Scientific Reports (Internet), 6, p.23295_1 - 23295_9, 2016/03

AA2016-0503.pdf:1.66MB

https://doi.org/10.1038/srep23295

We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, GeFe (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3 electrons are strongly hybridized with the Ge 4 states, and have a large orbital magnetic moment relative to the spin magnetic moment, namely / 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20 - 100K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.

Spin and orbital magnetic moments of Fe in the -type ferromagnetic semiconductor (In,Fe)As

小林 正起*; Anh, L. D.*; Hai, P. N.*; 竹田 幸治; 坂本 祥哉*; 門野 利治*; 岡根 哲夫; 斎藤 祐児; 山上 浩志; 原田 慈久*; et al.

Applied Physics Letters, 105(3), p.032403_1 - 032403_4, 2014/07

AA2015-0418.pdf:0.82MB

https://doi.org/10.1063/1.4890733

The electronic and magnetic properties of Fe atoms in the ferromagnetic semiconductor (In,Fe)As codoped with Be have been studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Fe edge. The XAS and XMCD spectra showed simple spectral line shapes similar to Fe metal, but the ratio of the orbital and spin magnetic moments estimated using the XMCD sum rules was significantly larger than that of Fe metal, indicating a significant orbital moment of Fe 3 electrons in (In,Fe)As:Be. The XMCD intensity as a function of magnetic field indicated hysteretic behavior of the superparamagnetic-like component due to discrete ferromagnetic domains. VC

Crystallization and preliminary X-ray diffraction studies of polyketide synthase-1 (PKS-1) from

田口 千穂; 田浦 太志*; 玉田 太郎; 正山 祥生; 正山 征洋*; 田中 宏幸*; 黒木 良太; 森元 聡*

Acta Crystallographica Section F, 64(3), p.217 - 220, 2008/03

https://doi.org/10.1107/S1744309108003096

Polyketide synthase-1 (PKS-1) is a novel type III polyketide synthase that catalyzes biosynthesis of the hexanoyl triacetic acid lactone in (Mexican strain). PKS-1 was overproduced in , purified and finally crystallized in two different space groups. The crystal obtained in 0.1 M HEPES buffer (pH 7.5) containing 0.2 M calcium acetate and 20% (w/v) polyethylene glycol 3350, diffracted to 1.65 resolution and belonged to space group 1 with unit-cell parameters of a = 54.3 , b = 59.3 , c = 62.6 , = 69, = 81, = 80. Another crystal obtained in 0.1 M HEPES buffer (pH 7.5) containing 0.2 M sodium chloride and 20% (w/v) polyethylene glycol 3350, diffracted to 1.55 resolution and belonged to the space group 222 with unit-cell parameters of a = 54.3 , b = 110 , c = 130 . These data will enable us to determine the crystal structure of PKS-1.

Fission yield measurement using multi-nucleon transfer reactions

廣瀬 健太郎; 西尾 勝久; 田中 翔也*; Leguillon, R.*; 牧井 宏之; 西中 一朗*; Orlandi, R.; 塚田 和明; Smallcombe, J.*; Vermeulen, M. J.*; et al.

no journal, , 

The multi-nucleon transfer reaction is very useful way to populate a multitude of nuclides in a wide excitation energy range. We have developed a measurement system at the JAEA tandem accelerator facility to obtain fission observables such as fission-fragment mass distributions (FFMD), prompt fission neutron multiplicities and so on. By identifying the ejectile, the initial compound nucleus is also identified. At high excitation energies, fission of nuclides produced via neutron emission from the initial compound nucleus also contribute to FFMD. In the present study, effects of the multi-chance fission on FFMDs were successfully separated by a combination of a systematic data set obtained from experiments using O beams and actinide targets and a dynamical fission calculation based on the fluctuation-dissipation model.