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Te
Wang, Y.*; 梶原 駿*; 松岡 秀樹*; Saika, B. K.*; 山神 光平*; 竹田 幸治; 和達 大樹*; 石坂 香子*; 岩佐 義宏*; 中野 匡規*
Nano Letters, 22(24), p.9964 - 9971, 2022/12
被引用回数：1 パーセンタイル：44.44(Chemistry, Multidisciplinary)In a conventional magnetic material, a long-range magnetic order develops in three dimensions, and reducing a layer number weakens its magnetism. Here we demonstrate anomalous layer-number-independent ferromagnetism down to the two-dimensional (2D) limit in a metastable phase of CrTe. We fabricated CrTe thin films by molecular-beam epitaxy and found that CrTe could host two distinct ferromagnetic phases characterized with different Curie temperatures (
). One is the bulk-like high- phase showing room-temperature ferromagnetism, which is consistent with previous studies. The other is the metastable low- phase with 
160 K, which exhibits a layer-number-independent down to the 2D limit in marked contrast with the conventional high- phase, demonstrating a purely 2D nature of its ferromagnetism. Such significant differences between two distinct phases could be attributed to a small variation in the doping level, making this material attractive for future ultracompact spintronics applications with potential gate-tunable room-temperature 2D ferromagnetism.
-
hybridization intertwined with anomalous ground state formation in the van der Waals itinerant magnet Fe
GeTe
山神 光平*; 藤澤 唯太*; Markel, P.-A.*; Barnaby, S.*; 角田 一樹; 竹田 幸治; 岡田 佳憲*
Physical Review B, 106(4), p.045137_1 - 045137_8, 2022/07
被引用回数：2 パーセンタイル：0(Materials Science, Multidisciplinary)FeGeTe is a van der Waals (vdW) coupled unconventional ferromagnetic metal with a high Curie temperature (
), exceeding 300 K. The formation of an anomalous ground state far below has attracted great interest, leading to a need to understand the spin-polarized electronic state near the Fermi energy (
) at low temperature. Despite recent extensive study, a microscopic understanding of the spin polarized electronic structure around has not been established yet due to the intrinsic complexity of both the crystal and band structures. In this work, we investigate the temperature dependence of element-specific soft X-ray magnetic circular dichroism (XMCD). Systematic temperature evolution in the XMCD signal from both magnetic Fe and its ligand Te is clearly observed. Importantly, the enhancement of the hybridization between Fe 3 and Te 5 states in the zero-magnetic field limit has been revealed. In light of the possible emergence of an exotic ground state, we discuss the temperature and magnetic field evolution of the element specific XMCD results.
symmetry in CeCu
Ge; Soft X-ray absorption and hard X-ray photoemission spectroscopy荒谷 秀和*; 中谷 泰博*; 藤原 秀紀*; 川田 萌樹*; 金井 惟奈*; 山神 光平*; 藤岡 修平*; 濱本 諭*; 久我 健太郎*; 木須 孝幸*; et al.
Physical Review B, 98(12), p.121113_1 - 121113_6, 2018/09
被引用回数：4 パーセンタイル：23.48(Materials Science, Multidisciplinary)We present a detailed study on the 
ground state symmetry of the pressure-induced superconductor CeCuGe probed by soft X-ray absorption and hard X-ray photoemission spectroscopy. The revised Ce ground states are determined as 
with 
in-plane rotational symmetry. This gives an in-plane magnetic moment consistent with the antiferromagnetic moment as reported in neutron measurements. Since the in-plane symmetry is the same as that for the superconductor CeCuSi, we propose that the charge distribution along the 
-axis plays an essential role in driving the system into a superconducting phase.
山崎 篤志*; 藤原 秀紀*; 橘 祥一*; 岩崎 大昌*; 東野 勇志*; 吉見 千秋*; 中川 広野*; 中谷 泰博*; 山神 光平*; 荒谷 秀和*; et al.
Physical Review B, 94(11), p.115103_1 - 115103_10, 2016/11
被引用回数：16 パーセンタイル：62.01(Materials Science, Multidisciplinary)軟X線角度分解光電子分光を用いて、Ruddlesden-Popper型イリジウム酸化物Sr
Ir
O
の3次元バンド構造を調べた。その結果、IrO面構造の次元性の増加と共に発現する金属-絶縁体転移に関する直接的な証拠を得た。この転移は、スピンー軌道結合により生じた
= 1/2バンドがフェルミエネルギーを横切ることにより生じる。入射光エネルギーを350eV以上走査することにより、SrIrO
の3次元フェルミ面形状及び、SrIrO
の
依存した光電子強度の振動を明らかにした。本手法は、電子状態の全体像の理解において非常に有効である。
thin films石上 啓介*; 吉松 公平*; 豊田 大介*; 滝沢 優*; 吉田 鉄平*; 芝田 悟朗*; 原野 貴幸*; 高橋 文雄*; 門野 利治*; Verma, V. K.*; et al.
Physical Review B, 92(6), p.064402_1 - 064402_5, 2015/08
被引用回数：41 パーセンタイル：84.12(Materials Science, Multidisciplinary)Thin films of the ferromagnetic metal SrRuO (SRO) show a varying easy magnetization axis depending on the epitaxial strain, and undergo a metal-to-insulator transition with decreasing film thickness. We have investigated the magnetic properties of SRO thin films with varying thicknesses fabricated on SrTiO(001) substrates by soft X-ray magnetic circular dichroism at the Ru M2,3 edge. Results have shown that, with decreasing film thickness, the film changes from ferromagnetic to nonmagnetic at around 3 monolayer thickness, consistent with previous magnetization and magneto-optical Kerr effect measurements. The orbital magnetic moment perpendicular to the film was found to be 0.1
B/Ru, and remained nearly unchanged with decreasing film thickness while the spin magnetic moment decreases. A mechanism for the formation of the orbital magnetic moment is discussed based on the electronic structure of the compressively strained SRO film.
-orbital symmetry of the ground state in Yb compounds by linear dichroism in core-level photoemission森 健雄*; 北山 賢*; 金井 惟奈*; 内免 翔*; 藤原 秀紀*; 東谷 篤志*; 玉作 賢治*; 田中 新*; 寺嶋 健成*; 今田 真*; et al.
Journal of the Physical Society of Japan, 83(12), p.123702_1 - 123702_5, 2014/12
被引用回数：15 パーセンタイル：68.36(Physics, Multidisciplinary)正方晶YbRhSi及びYbCuSiに対して、角度分解内殻光電子分光における直線偏光線二色性を発見し、それにより、基底状態の強相関4軌道の対称性を明らかにした。理論計算から、この線二色性は結晶場効果に由来する異方的な電荷分布を反映することが示された。結晶場の第一励起エネルギーよりもはるかに低温での測定により、両物質の基底状態の4波動関数の決定に成功した。更に、温度依存性測定により、励起状態の対称性についても調べた。
Sr
MnO thin films studied by X-ray magnetic circular dichroism芝田 悟朗*; 吉松 公平*; 坂井 延寿*; Singh, V. R.*; Verma, V.*; 石上 啓介*; 原野 貴幸*; 門野 利治*; 竹田 幸治; 岡根 哲夫; et al.
Physical Review B, 89(23), p.235123_1 - 235123_5, 2014/06
被引用回数：19 パーセンタイル：63.93(Materials Science, Multidisciplinary)Metallic transition-metal oxides undergo a metal-to-insulator transition (MIT) as the film thickness decreases across a critical thickness of several monolayers (MLs), but its driving mechanism remains controversial. We have studied the thickness-dependent MIT of the ferromagnetic metal LaSrMnO by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The results suggest that the ferromagnetic phase gradually and most likely inhomogeneously turns into the paramagnetic phase and both phases abruptly become insulating at the critical thickness.
