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Negative Te spin polarization responsible for ferromagnetic order in the doped topological insulator V$$_{0.04}$$(Sb$$_{1-x}$$Bi$$_{x}$$)$$_{1.96}$$Te$$_{3}$$

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

 パーセンタイル:100(Materials Science, Multidisciplinary)

We investigate the microscopic origin of ferromagnetism coupled with topological insulators in V-doped (Sb,Bi)$$_{2}$$Te$$_{3}$$ 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${it p}$ and V 3${it d}$ majority spin states at the Fermi energy, consistent with the Zener-type ${it p}$-${it d}$ 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 ${it p}$ 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.


Antiferromagnetic interaction between paramagnetic Co ions in the diluted magnetic semiconductor Zn$$_{1-x}$$Co$$_x$$O

小林 正起*; 石田 行章*; Hwang, J. I.*; 長船 義敬*; 藤森 淳*; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 小林 啓介*; 佐伯 洋昌*; et al.

Physical Review B, 81(7), p.075204_1 - 075204_7, 2010/02


 被引用回数:18 パーセンタイル:31.68(Materials Science, Multidisciplinary)

The magnetic properties of Zn$$_{1-x}$$Co$$_x$$O (x=0.07 and 0.10) thin films, which were homoepitaxially grown on a ZnO(0001) substrates with varying relatively high oxygen pressure, have been investigated using X-ray magnetic circular dichroism (XMCD) at Co 2p core-level absorption edge. The magnetic-field and temperature dependences of the XMCD intensity are consistent with the magnetization measurements, indicating that except for Co there are no additional sources for the magnetic moment, and demonstrate the coexistence of paramagnetic and ferromagnetic components in the homoepitaxial Zn$$_{1-x}$$Co$$_x$$O thin films. The analysis of the XMCD intensities using the Curie-Weiss law reveals the presence of antiferromagnetic interaction between the paramagnetic Co ions. Missing XMCD intensities and magnetization signals indicate that most of Co ions are nonmagnetic probably because they are strongly coupled antiferromagnetically with each other.


Hybridization between the conduction band and 3$$d$$ orbitals in the oxide-based diluted magnetic semiconductor In$$_{2-x}$$V$$_x$$O$$_3$$

小林 正起*; 石田 行章*; Hwang, J. I.*; Song, G. S.*; 滝沢 優*; 藤森 淳; 竹田 幸治; 大河内 拓雄*; 岡根 哲夫; 斎藤 祐児; et al.

Physical Review B, 79(20), p.205203_1 - 205203_5, 2009/05

 被引用回数:4 パーセンタイル:74.29(Materials Science, Multidisciplinary)

The electronic structure of In$$_{2-x}$$V$$_x$$O$$_3$$ ($$x=0.08$$) has been investigated by photoemission spectroscopy and X-ray absorption spectroscopy (XAS). The V $$2p$$ core-level photoemission and XAS spectra revealed that the V ion is in the trivalent state, which is the same valence state as that of In in In$$_2$$O$$_3$$. The V $$3d$$ partial density of states obtained by the resonant photoemission technique showed a sharp peak above the O $$2p$$ band. While the O $$1s$$ XAS spectrum of In$$_{2-x}$$V$$_x$$O$$_3$$ was similar to that of In$$_2$$O$$_3$$, there were differences in the In $$3p$$ and $$3d$$ XAS spectra between the V-doped and pure In$$_2$$O$$_3$$. The observations give clear evidence for hybridization between the In-derived conduction band and the V $$3d$$ orbitals in In$$_{2-x}$$V$$_x$$O$$_3$$.


Local electronic structure of Cr in the II-VI diluted ferromagnetic semiconductor Zn$$_{1-x}$$Cr$$_x$$Te

小林 正起*; 石田 行章*; Hwang, J. I.*; Song, G. S.*; 藤森 淳; Yang, C. S.*; Lee, L.*; Lin, H.-J.*; Huang, D.-J.*; Chen, C. T.*; et al.

New Journal of Physics (Internet), 10, p.055011_1 - 055011_15, 2008/05

 被引用回数:11 パーセンタイル:37.82(Physics, Multidisciplinary)

The electronic structure of the Cr ions in the diluted ferromagnetic semiconductor Zn$$_{1-x}$$Cr$$_x$$Te ($$x$$=0.03 and 0.15) thin films has been investigated using X-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy (PES). The line shape of the Cr $$2p$$ XMCD spectra is independent of $$H$$, $$T$$, and $$x$$, indicating that the ferromagnetism is originated from the same electronic states of the Cr ion. Cluster-model analysis indicates that the ferromagnetic XMCD signal is originated from Cr ions substituted for the Zn site. The Cr $$3d$$ partial density of states extracted using Cr $$2p to 3d$$ resonant PES shows a broad feature near the top of the valence band, suggesting strong $$s$$,$$p$$-$$d$$ hybridization. Based on these findings, we conclude that double exchange mechanism cannot explain the ferromagnetism in Zn$$_{1-x}$$Cr$$_{x}$$Te.


Soft X-ray magnetic circular dichroism study of weakly ferromagnetic Zn$$_{1-x}$$V$$_{x}$$O thin film

石田 行章*; Hwang, J. I.*; 小林 正起*; 竹田 幸治; 間宮 一敏*; 岡本 淳*; 藤森 伸一; 岡根 哲夫; 寺井 恒太*; 斎藤 祐児; et al.

Applied Physics Letters, 90(2), p.022510_1 - 022510_3, 2007/01

 被引用回数:20 パーセンタイル:33.56(Physics, Applied)



Characterization of magnetic components in the diluted magnetic semiconductor Zn$$_{1-x}$$Co$$_x$$O by X-ray magnetic circular dichroism

小林 正起*; 石田 行章*; Hwang, J. I.*; 溝川 貴司*; 藤森 淳*; 間宮 一敏*; 岡本 淳*; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; et al.

Physical Review B, 72(20), p.201201_1 - 201201_4, 2005/11

 被引用回数:130 パーセンタイル:3.06(Materials Science, Multidisciplinary)



High-energy spectroscopic study of the III-V nitride-based diluted magnetic semiconductor Ga$$_{1-x}$$Mn$$_{x}$$N

Hwang, J. I.*; 石田 行章*; 小林 正起*; 平田 玄*; 田久保 耕*; 溝川 貴司*; 藤森 淳; 岡本 淳; 間宮 一敏*; 斎藤 祐児; et al.

Physical Review B, 72(8), p.085216_1 - 085216_6, 2005/08


 被引用回数:60 パーセンタイル:10.73(Materials Science, Multidisciplinary)


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