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論文

Microscopic origin of the spin-reorientation transition in the kagome topological magnet TbMn$$_{6}$$Sn$$_{6}$$

Huang, Z.*; Wang, W.*; Ye, H.*; Bao, S.*; Shangguan, Y.*; Liao, J.*; Cao, S.*; 梶本 亮一; 池内 和彦*; Deng, G.*; et al.

Physical Review B, 109(1), p.014434_1 - 014434_9, 2024/01

TbMn$$_{6}$$Sn$$_{6}$$ is a correlated topological magnet with a Mn-based kagome lattice, in which a Chern gap opens at the Dirac point at low temperatures. The magnetic moment direction of the ferrimagnetic order changes from in the kagome plane to the out-of-plane upon cooling, which is essential for generating the Chern gap, but the underlying mechanism for the spin reorientation remains elusive. Here, we investigate the spin-reorientation transition in TbMn$$_{6}$$Sn$$_{6}$$ using neutron scattering. We provide direct evidence for the spin-reorientation transition and unveil the coexistence of two Tb modes at 200 K. To account for these results, we put forward a model based on SU(N) spin-wave theory, in which there is a temperature evolution of the ground state Tb $$4f$$ orbitals, driven by the crystalline electric field, single-ion anisotropy, and exchange interactions between Tb and Mn ions. Our findings shed light on the complex magnetism of TbMn$$_{6}$$Sn$$_{6}$$, despite its relatively simple ground state magnetic structure, and provide insights into the mechanisms for tuning magnetic topological materials.

論文

Overall approaches and experiences of first-time participants in the Nuclear Forensics International Technical Working Group's Fourth Collaborative Material Exercise (CMX-4)

Ho, D. M. L.*; Nelwamondo, A. N.*; 大久保 綾子; Rameb$"a$ck, H.*; Song, K.*; Han, S.-H.*; Hancke, J. J.*; Holmgren, S.*; Jonsson, S.*; 片岡 修; et al.

Journal of Radioanalytical and Nuclear Chemistry, 315(2), p.353 - 363, 2018/02

 被引用回数:1 パーセンタイル:21.23(Chemistry, Analytical)

国際核鑑識作業グループが主催する第4回核鑑識共同試料分析演習には、過去最大の17か国からの参加があり、このうち7か国は初めての参加であった。本稿では、演習に初めて参加した5か国のラボラトリが、演習で実施した分析試料の準備および分析内容について情報を共有した。核鑑識共同試料分析演習は、各ラボラトリで確立した分析法のテスト、他の目的で確立した方法の核鑑識への適用化、分析技術の修練に非常に有用であることが確認された。また、演習実施後に開催されたレビュー会合によって、核鑑識シグネチャとその解釈に関する理解を深めることができた。

論文

The Application of radiochronometry during the 4th collaborative materials exercise of the nuclear forensics international technical working group (ITWG)

Kristo, M. J.*; Williams, R.*; Gaffney, A. M.*; Kayzar-Boggs, T. M.*; Schorzman, K. C.*; Lagerkvist, P.*; Vesterlund, A.*; Rameb$"a$ck, H.*; Nelwamondo, A. N.*; Kotze, D.*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 315(2), p.425 - 434, 2018/02

 被引用回数:12 パーセンタイル:82.06(Chemistry, Analytical)

最新の核鑑識国際共同試料分析演習では、低濃縮ウラン試料について、10か国の核鑑識ラボラトリーが精製年代測定を実施して良好な結果を得た。これらの測定のうち、3つの異なる核種ペアを用いた精製年代測定も実施された。10か国の核鑑識ラボラトリーが提出した精製年代測定の結果は、実際の精製日と概ね一致した。また、質量分析法による結果は、放射線計測法を用いたものに比べて、高精度な結果を示した。さらに、一部のラボラトリーによって示された$$^{235}$$U-$$^{231}$$Pa法と$$^{234}$$U-$$^{230}$$Th法による精製年代測定の結果の一致は、結果の確証性を高めた。

論文

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe$$_{2-x}$$T$$_{x}$$As$$_{2}$$ ($$T$$ = Co,Ni)

Tam, D. M.*; Song, Y.*; Man, H.*; Cheung, S. C.*; Yin, Z.*; Lu, X.*; Wang, W.*; Frandsen, B. A.*; Liu, L.*; Gong, Z.*; et al.

Physical Review B, 95(6), p.060505_1 - 060505_6, 2017/02

 被引用回数:23 パーセンタイル:71.84(Materials Science, Multidisciplinary)

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe$$_{2-x}$$T$$_{x}$$As$$_{2}$$ and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe$$_{1.9}$$Co$$_{0.1}$$As$$_2$$, and a 15% increase for BaFe$$_{1.915}$$Ni$$_{0.085}$$As$$_2$$. We also observe an increase of the AF ordering temperature ($$T_N$$) of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

論文

Status and result of the KSTAR upgrade for the 2010's campaign

Yang, H. L.*; Kim, Y. S.*; Park, Y. M.*; Bae, Y. S.*; Kim, H. K.*; Kim, K. M.*; Lee, K. S.*; Kim, H. T.*; Bang, E. N.*; Joung, M.*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

韓国超伝導トカマク先進研究装置(KSTAR)における高楕円度でダイバータ配位を有するプラズマ生成を目指した2010年の運転のため、プラズマ形状制御に不可欠なハードウェア・システムが新たに据え付けられ改良された。この論文では、改良されたシステムの一般的な構成の概要を述べる。さらに、システムにおいてキーとなる幾つかの性能と試験結果についても報告する。

論文

Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nanoparticles

片岡 隆史*; 小林 正起*; 坂本 勇太*; Song, G. S.*; 藤森 淳*; Chang, F.-H.*; Lin, H.-J.*; Huang, D. J.*; Chen, C. T.*; 大河内 拓雄*; et al.

Journal of Applied Physics, 107(3), p.033718_1 - 033718_7, 2010/02

AA2009-0977.pdf:1.0MB

 被引用回数:53 パーセンタイル:85.88(Physics, Applied)

We have studied the electronic structure of Fe-doped ZnO nanoparticles, which have been reported to show ferromagnetism at room temperature, by X-ray photoemission spectroscopy (XPS), resonant photoemission spectroscopy (RPES), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe$$^{3+}$$ ionic state with mixture of a small amount of Fe$$^{2+}$$ and that Fe$$^{3+}$$ ions are dominant in the surface region of the nanoparticles. It is shown that the room temperature ferromagnetism in the Fe-doped ZnO nanoparticles is primarily originated from the antiferromagnetic coupling between unequal amounts of Fe$$^{3+}$$ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of $$sim$$2-3 nm.

論文

Experimental observation of bulk band dispersions in the oxide semiconductor ZnO using soft X-ray angle-resolved photoemission spectroscopy

小林 正起*; Song, G.-S.*; 片岡 隆史*; 坂本 勇太*; 藤森 淳; 大河内 拓雄*; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 山上 浩志; et al.

Journal of Applied Physics, 105(12), p.122403_1 - 122403_4, 2009/06

BB2009-1947.pdf:0.84MB

 被引用回数:11 パーセンタイル:45.02(Physics, Applied)

ZnO is one of the most promising oxide semiconductors for applications to semiconductor electronics, especially for optical devices. Their inexpensiveness and environmental safety are also advantages for practical applications. The surface electronic structure of ZnO has been investigated so far using angle-resolved photoemission spectroscopy (ARPES) in the ultraviolet ray region (less than 150 eV), although those measurements are surface sensitive. Considering their potentiality of ZnO for extensive applications, it is desired to investigate the bulk electronic structure of ZnO experimentally. In this work, we have performed soft X-ray (SX) ARPES measurements on a ZnO thin film in order to probe the bulk electronic structure. All the obtained band dispersion reflects the hexagonal Brillouin zone of ZnO, indicating we succeeded in the observation of the band dispersion of ZnO by SX-ARPES.

論文

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:7 パーセンタイル:33.25(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$$_3$$.

論文

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:15 パーセンタイル:64.43(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.

論文

Photoemission and X-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)$$_3$$O$$_4$$ thin films exhibiting photoinduced magnetization

小林 正起*; 大木 康弘*; 滝沢 優*; Song, G. S.*; 藤森 淳; 竹田 幸治; 寺井 恒太*; 岡根 哲夫; 藤森 伸一; 斎藤 祐児; et al.

Applied Physics Letters, 92(8), p.082502_1 - 082502_3, 2008/02

 被引用回数:12 パーセンタイル:44.67(Physics, Applied)

By means of photoemission and X-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)$$_{3}$$O$$_{4}$$ thin films, which exhibits a cluster glass behavior with a spin-freezing temperature $$T_f$$ of $$sim 230$$ K and photo-induced magnetization (PIM) below $$T_f$$. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe$$^{3+}$$) and tetravalent (Ti$$^{4+}$$), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe$$^{2+}$$ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.

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