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竹田 幸治; 大矢 忍*; Pham, N. H.*; 小林 正起*; 斎藤 祐児; 山上 浩志; 田中 雅明*; 藤森 淳*
Journal of Applied Physics, 128(21), p.213902_1 - 213902_11, 2020/12
In order to understand the mechanism of the ferromagnetism in GaMn
As ((Ga,Mn)As), we have investigated the magnetic behavior on a microscopic level through systematic temperature (
) and magnetic-field (
) dependent soft X-ray magnetic circular dichroism (XMCD) experiments at the Mn
absorption edges. The
and
dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations and different Curie temperature (
) values. In particular, the SPM component develops well above
, indicating that local FM regions are formed well above
. The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families.
斎藤 祐児; 藤原 秀紀*; 保井 晃*; 門野 利治*; 菅原 仁*; 菊地 大輔*; 佐藤 英行*; 菅 滋正*; 山崎 篤志*; 関山 明*; et al.
Physical Review B, 102(16), p.165152_1 - 165152_8, 2020/10
被引用回数:0Through a high-precision soft X-ray magnetic circular dichroism (XMCD) study of the intermediate-valence compound SmOsSb
, we show our successful approach of revealing unprecedented details of Kondo screening below a characteristic temperature of
20 K in the paramagnetic phase. The multiplet XMCD structure at the Sm
edge sensitive to the 4
configuration enabled us to observe a clear difference between the temperature evolution above and below
with one- and two-component behavior, respectively. Our findings are in strong contrast to the conventional Kondo crossover that coincides with the valence transition, but are qualitatively accounted for by theoretical XMCD predictions combined with the two-fluid phenomenology recently proposed. This work contributes to the large context of Kondo physics that is closely related to quantum criticality in heavy fermion systems.
吉川 智己*; Antonov, V. N.*; 河野 嵩*; 鹿子木 将明*; 角田 一樹; 宮本 幸治*; 竹田 幸治; 斎藤 祐児; 後藤 一希*; 桜庭 裕弥*; et al.
Physical Review B, 102(6), p.064428_1 - 064428_7, 2020/08
被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy were applied at the Ge (Ga) edge to unravel the spin-resolved unoccupied electronic states of Co
MnGe (Ga). Complicated spectral features were observed in both XAS and XMCD spectra. For their interpretation, we compared the experimental XAS and XMCD spectra with the calculated Ge (Ga) 4
and 4
orbital partial density of states. The comparison enabled a qualitative explanation of the XMCD spectra as the difference between the majority and minority-spin unoccupied density of states summed over the 4
and 4
orbitals. Our finding provides a new approach to uncover the spin-split partial density of states above the Fermi level.
Shikin, A. M.*; Estyunin, D. A.*; Klimovskikh, I. I.*; Filnov, S. O.*; Kumar, S.*; Schwier, E. F.*; 宮本 幸治*; 奥田 太一*; 木村 昭夫*; 黒田 健太*; et al.
Scientific Reports (Internet), 10, p.13226_1 - 13226_13, 2020/08
被引用回数:0 パーセンタイル:100(Multidisciplinary Sciences)Modification of the gap at the Dirac point (DP) in axion antiferromagnetic topological insulator MnBiTe
and its electronic and spin structure have been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation at various temperatures, light polarizations and photon energies. We have distinguished both large and reduced gaps at the DP in the ARPES dispersions, which remain open above the N
el temperature of
= 24.5 K. We propose that the gap above
remains open due to a short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for the large gap sample and apparently significantly reduced effective magnetic moment for the reduced gap sample.
伊藤 啓太*; 安富 陽子*; Zhu, S.*; Nurmamat, M.*; 田原 昌樹*; 都甲 薫*; 秋山 了太*; 竹田 幸治; 斎藤 祐児; 小口 多美夫*; et al.
Physical Review B, 101(10), p.104401_1 - 104401_8, 2020/03
被引用回数:1 パーセンタイル:31.73(Materials Science, Multidisciplinary)Spintronics devices utilizing a magnetic domain wall motion have attracted increasing attention, and ferrimagentic materials with almost compensated magnetic moments are highly required to realize the fast magnetic domain wall motion. Here, we report a key function for this purpose in anti-perovskite CoMn
N films. Perpendicular magnetization emerges for
, and the saturation magnetization reaches a minimum value at
.
河野 嵩*; 鹿子木 将明*; 吉川 智己*; Wang, X.*; 角田 一樹*; 宮本 幸治*; 室 隆桂之*; 竹田 幸治; 斎藤 祐児; 後藤 一希*; et al.
Physical Review B, 100(16), p.165120_1 - 165120_6, 2019/10
被引用回数:1 パーセンタイル:76.22(Materials Science, Multidisciplinary)Resonant photoelectron spectroscopy at the Co and Mn 2 core absorption edges of half-metallic Co
MnGe has been performed to determine the element-specific density of states (DOS). A significant contribution of the Mn 3
partial DOS near the Fermi level (
) was clarified by measurement at the Mn 2
absorption edge. Further analysis by first-principles calculation revealed that it has
symmetry, which must be responsible for the electrical conductivity along the line perpendicular to the film plane. The dominant normal Auger contribution observed at the Co 2
absorption edge indicates delocalization of photoexcited Co 3
electrons. The difference in the degrees of localization of the Mn 3
and Co 3
electrons in Co
MnGe is explained by the first-principles calculation.
角田 一樹*; 鹿子木 将明*; Reimann, J.*; Nurmamat, M.*; 後藤 伸一*; 竹田 幸治; 斎藤 祐児; Kokh, K. A.*; Tereshchenko, O. E.*; Gdde, J.*; et al.
New Journal of Physics (Internet), 21(9), p.093006_1 - 093006_8, 2019/09
被引用回数:1 パーセンタイル:65.14(Physics, Multidisciplinary)We systematically investigate the magnetic, structural and electronic properties and the ultrafast carrier dynamics in a series of V-doped SbTe
samples of composition Sb
V
Te
with x = 0, 0.015 and 0.03. Element specific X-ray magnetic circular dichroism signifies that the ferromagnetism of V-doped Sb
Te
is governed by the p-d hybridization between the host carrier and the magnetic dopant. Time- and angle-resolved photoemission spectroscopy has revealed that the V impurity induced states underlying the topological surface state (TSS) add scattering channels that significantly shorten the duration of transient surface electrons down to 100 fs scale. This is in a sharp contrast to the prolonged duration reported for pristine samples though the TSS is located inside the bulk energy gap of the host in either magnetic or non-magnetic cases. It implies the presence of a mobility gap in the bulk energy gap region of the host material.
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
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.
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
被引用回数:4 パーセンタイル:33.43(Materials Science, Multidisciplinary)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 would be responsible for the ferromagnetic order in this material.
Ye, M.*; Xu, T.*; Li, G.*; Qiao, S.*; 竹田 幸治; 斎藤 祐児; Zhu, S.-Y.*; Nurmamat, M.*; 角田 一樹*; 石田 行章*; et al.
Physical Review B, 99(14), p.144413_1 - 144413_7, 2019/04
被引用回数:5 パーセンタイル:43.12(Materials Science, Multidisciplinary)We investigate the microscopic origin of ferromagnetism coupled with topological insulators in V-doped (Sb,Bi)Te
employing X-ray magnetic circular dichroism and angle-resolved two-photon photoemission spectroscopies, combined with first-principles calculations. We found an magnetic moment at the Te site anti-parallel to that of the V and Sb sites, which plays a key role in the ferromagnetic order. We ascribe it to the hybridization between Te 5
and V 3
majority spin states at the Fermi energy, consistent with the Zener-type
-
exchange interaction scenario. The substitution of Bi for Sb suppresses the bulk ferromagnetism by introducing extra electron carriers in the majority spin channel of the Te
states that compensates the antiparallel magnetic moment on the Te site. Our findings reveal important clues to designing magnetic topological insulators with higher Curie temperature that work under ambient conditions.
Shikin, A. M.*; Estyunin, D. A.*; Surnin, Yu. I.*; Koroleva, A. V.*; Shevchenko, E. V.*; Kokh, K. A.*; Tereshchenko, O. E.*; Kumar, S.*; Schwier, E. F.*; 島田 賢也*; et al.
Scientific Reports (Internet), 9(1), p.4813_1 - 4813_17, 2019/03
被引用回数:6 パーセンタイル:26.52(Multidisciplinary Sciences)A new kind of magnetically-doped antiferromagnetic (AFM) topological insulators (TIs), BiGd
Sb
Te
, has been studied by angle-resolved photoemission, superconducting magnetometry (SQUID) and X-ray magnetic circular dichroism (XMCD). It has been shown that this TI is characterized by the Dirac gap at the Fermi level. In the paramagnetic phase, a surface magnetic layer is supposed to develop, where the coupling between the Gd magnetic moments is mediated by the topological surface states (TSSs). This assumption can be confirmed by opening a gap at the Dirac point indicated by the surface-sensitive ARPES, a weak hysteresis loop measured by SQUID, the XMCD showing a surface magnetic moment and the temperature dependence of electrical resistance demonstrating a mid-gap semiconducting behavior, which correlates with the temperature dependence of the surface magnetization and confirms the conclusion that only TSSs are located at the Fermi level.
藤森 伸一; 小畠 雅明; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*
Physical Review B, 99(3), p.035109_1 - 035109_5, 2019/01
被引用回数:3 パーセンタイル:56.85(Materials Science, Multidisciplinary)In the present study, we have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the
4
-5
resonant photoemission spectroscopy. Obtained
pDOS exhibit a systematic trend depending on the physical properties of compounds: Although the coherent peak at the Fermi level can be explained by the band-structure calculation, an incoherent peak emerges on the higher binding energy side (
) in the cases of localized and heavy fermion compounds. The intensity and energy position of the incoherent peak is increased and shifted to a higher binding energy as the localization of the
state increases. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard-
type mechanism takes an essential role in the
electronic structure of actinide materials.
藤森 伸一; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*
Progress in Nuclear Science and Technology (Internet), 5, p.82 - 85, 2018/11
One of the most remarkable properties of actinide compounds is the coexistence of superconductivity and magnetic ordering which has been realized in several strongly-correlated uranium based compounds. In these compounds, both superconductivity and magnetic ordering originate from U 5f states. To understand the origin of the coexistence as well as the mechanism of the superconductivity, it is essential to reveal their U 5f electronic structures. In this presentation, the U 5f electronic structures of heavy Fermion superconductors UPdAl
and URu
Si
studied by photoelectron spectroscopy using soft X-rays from SPring-8 BL23SU are presented. For UPd
Al
, U 4d-5f resonant photoemission experiment was performed, and its partial U 5f spectrum was revealed experimentally. Furthermore, we have applied the three-dimentional ARPES to the hidden order compound URu
Si
, and revealed its complete 3D electronic structure in the paramagnetic phase. Their electronic structures are discussed based on these results.
竹田 幸治; 岡根 哲夫; 斎藤 祐児; 山上 浩志; 山本 悦嗣; 芳賀 芳範
Progress in Nuclear Science and Technology (Internet), 5, p.171 - 174, 2018/11
In order to investigate the electronic and magnetic states of UGe element-specifically, we have performed soft X-ray magnetic circular dichroism experiments at the U N
and Ge L
absorption edges. We have detected the XMCD signals at both the U and Ge sites and observed clear hysteresis loops in the ferromagnetic (FM) state at T = 5.5 K. From the branching ratio B, it is found that the occupation number of 5f electrons (n
) in UGe
is close to 3. In addition, applying the magneto-optical sum rules analysis to the XMCD spectrum at the U N
edges, the ratio of orbital magnetic moment to the spin magnetic moment (-M
/M
) is estimated to be 2.17. These values of B and -M
/M
are comparable compared with the results of other FM superconductors: URhGe and UCoGe
堀尾 眞史*; 竹田 幸治; 並木 宏允*; 片桐 隆雄*; 若林 勇希*; 坂本 祥哉*; 野中 洋亮*; 芝田 悟朗*; 池田 啓祐*; 斎藤 祐児; et al.
Journal of the Physical Society of Japan, 87(10), p.105001_1 - 105001_2, 2018/10
被引用回数:1 パーセンタイル:77.53(Physics, Multidisciplinary)We have performed X-ray magnetic circular dichroism (XMCD) measurements on the iron-based superconductor SrVFeAsO
to study the origin of weak ferromagnetism (WFM) reported for this compound. While Fe 3d electrons show a magnetic response similar to the other iron pnictides, signals from V 3d electrons remain finite at zero magnetic field and may be responsible for the WFM.
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
被引用回数:3 パーセンタイル:70.78(Materials Science, Multidisciplinary)We study the electronic structure and magnetic properties of epitaxial (NiCo
)Fe
O
(111) layers with thicknesses
= 1.7 - 5.2 nm grown on Al
O
(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.
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:3 パーセンタイル:64.52(Materials Science, Multidisciplinary)We present a detailed study on the ground state symmetry of the pressure-induced superconductor CeCu
Ge
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 CeCu
Si
, we propose that the charge distribution along the
-axis plays an essential role in driving the system into a superconducting phase.
竹田 幸治; 斎藤 祐児; 岡根 哲夫; 山上 浩志; 松田 達磨*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦*
Physical Review B, 97(18), p.184414_1 - 184414_7, 2018/05
被引用回数:1 パーセンタイル:87.78(Materials Science, Multidisciplinary)We have performed soft X-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U 4-5
(
) and Co 2
-3
(
) absorption edges in order to investigate the magnetic properties of the U 5
and Co 3
electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co 3
electrons is unusually large. Through the systematic temperature (
)- and magnetic field (
)-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of
and
(M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was observed clearly under 15 K at
. The value of the
and its
-dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings show clearly that the role of the Co 3
electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.
中谷 泰博*; 荒谷 秀和*; 藤原 秀紀*; 森 健雄*; 鶴田 篤史*; 橘 祥一*; 山口 貴司*; 木須 孝幸*; 山崎 篤志*; 保井 晃*; et al.
Physical Review B, 97(11), p.115160_1 - 115160_7, 2018/03
被引用回数:1 パーセンタイル:87.78(Materials Science, Multidisciplinary)We present clear experimental evidence for the momentum-dependent heavy fermionic electronic structures of the 4-based strongly correlated system CeNi
Ge
by soft X-ray angle-resolved photoemission spectroscopy. A comparison between the experimental three-dimensional quasiparticle dispersion of LaNi
Ge
and CeNi
Ge
has revealed that heavy fermionic electronic structures are seen in the region surrounding at a specific momentum. Furthermore, the wave vectors between the observed "heavy spots" are consistent with a result of neutron scattering reflecting magnetic correlations, which could be a trigger of the superconductivity in CeNi
Ge
.
高田 郁弥*; 伊藤 啓太*; 竹田 幸治; 斎藤 祐児; 高梨 弘毅*; 木村 昭夫*; 末益 崇*
Physical Review Materials (Internet), 2(2), p.024407_1 - 024407_5, 2018/02
被引用回数:7 パーセンタイル:43.2(Materials Science, Multidisciplinary)X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism measurements were performed at the Ni and Fe absorption edges for Ni
Fe
N (
= 1 and 3) epitaxial films. Shoulders at approximately 2 eV above the Ni
main peaks in the XAS spectrum of Ni
FeN were interpreted to originate from hybridization of orbitals between Ni 3
at face-centered (II) sites and N 2
at body-centered sites, while such features were missing in NiFe
N film. Similar shoulders were observed at Fe
edges in both films. Hence, Ni atoms preferentially occupied corner (I) sites, where the hybridization was weak because of the relatively long distance between Ni at I sites and N atoms. The relatively large magnetic moment deduced from sum-rule analysis of NiFe
N also showed a good agreement with the presence of Ni atoms at I sites.