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.

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.

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.

Manifestation of electron correlation effect in 5 states of uranium compounds revealed by 4-5 resonant photoelectron spectroscopy

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

https://doi.org/10.1103/PhysRevB.99.035109

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.

Local magnetic states of the weakly ferromagnetic iron-based superconductor SrVFeAsO studied by X-ray magnetic circular dichroism

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

https://doi.org/10.7566/JPSJ.87.105001

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.

Electronic structure of ThRuSi studied by angle-resolved photoelectron spectroscopy; Elucidating the contribution of U 5 states in URuSi

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; 松本 裕司*; 山本 悦嗣; 立岩 尚之; et al.

Physical Review B, 96(12), p.125117_1 - 125117_9, 2017/09

https://doi.org/10.1103/PhysRevB.96.125117

The Fermi surface and band structure of have been studied by angle resolved photoelectron spectroscopy (ARPES) with the incident photon energies of = 665-735 eV. Detailed band structure and the three-dimensional shape of the Fermi surface were derived experimentally, and they are quantitatively explained by the band-structure calculation based on the density functional approximation. Comparison of the experimental ARPES spectra of with those of shows that they have considerably different spectral profiles particularly in the energy range of - 1 eV. Some energy bands with their energy dispersions of about 1 eV observed in are missing in the ARPES spectra of measured along the same high symmetry line of Brillouin zone, suggesting that U 5 states form these bands in . The relationship between the ARPES spectra of and is very different from the case between and where their intrinsic difference is limited only in the very vicinity of the Fermi energy. The present result argues that the U 5 electrons in have strong hybridization with ligand states, and essentially have an itinerant character.

Element specific electronic states and spin-flip-like behavior of Ce in (CeGd)Ni composed of heavy fermion CeNi and ferri-magnet GdNi through XMCD method

矢野 一雄*; 岡根 哲夫; 竹田 幸治; 山上 浩志; 藤森 淳; 西村 克彦*; 佐藤 清雄*

Physica B; Condensed Matter, 515, p.118 - 125, 2017/06

https://doi.org/10.1016/j.physb.2017.03.012

CeNi, GdNi、並びにCeGdNiについて、構成元素の電子状態を軟X線吸収磁気円二色性(XMCD)測定により調べた。実験の結果、この系では、Gd 4f電子だけでなく、NI 3d電子並びにCe 4f電子も磁性も有しており、NI並びにCeの磁気モーメントはGdの磁気モーメントとは反平行にカップリングしていることがわかった。Ceの磁気モーメントは、いったん飽和した後、2T以上の磁場領域で減少していくが、これはスピンフリップ挙動と考えられる。サムルール解析からは、Gd 4f電子とNi 3d電子に小さい軌道磁気モーメントが残っていることが示唆された。

Origin of the large positive magnetoresistance of GeMn granular thin films

若林 勇希*; 秋山 了太*; 竹田 幸治; 堀尾 眞史*; 芝田 悟朗*; 坂本 祥哉*; 伴 芳祐*; 斎藤 祐児; 山上 浩志; 藤森 淳*; et al.

Physical Review B, 95(1), p.014417_1 - 014417_6, 2017/01

https://doi.org/10.1103/PhysRevB.95.014417

GeMn (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). The microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of X-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.

Electronic structures of uranium compounds studied by soft X-ray photoelectron spectroscopy

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

Journal of the Physical Society of Japan, 85(6), p.062001_1 - 062001_33, 2016/06

https://doi.org/10.7566/JPSJ.85.062001

The electronic structures of uranium-based compounds are studied by photoelectron spectroscopies with soft X-ray synchrotron radiation. Angle-resolved photoelectron spectroscopy with soft X-rays made it possible to directly observe their bulk band structures and Fermi surfaces. It is shown that the band structure and Fermi surface of itinerant compounds are quantitatively explained by the band-structure calculation treating all U 5 electrons as being itinerant. Furthermore, the overall electronic structures of heavy Fermion compounds are also explained by the band-structure calculation although there exist some disagreements which might be originated from the electron correlation effect. This suggests that the itinerant description of U states is an appropriate starting point for their description. The local electronic structures of uranium site are probed by the core-level photoelectron spectroscopy with soft X-rays. The comparisons of core-level spectra of these compounds with typical itinerant and localized compounds suggest that the local electronic structures of most of itinerant and heavy Fermion compounds are close to U 5 configuration.

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.