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平 義隆*; 杉田 健人*; 岡野 泰彬*; 平出 哲也
no journal, ,
超短パルスガンマ線を陽電子消滅分光法(PAS)に適用した。ガンマ線誘起PAS(GiPAS)と呼ばれる高エネルギーガンマ線を使用するPASには、放射性同位元素を使用するPASと比較していくつかの利点がある。(i)陽電子は、材料への透過性が高いガンマ線の照射による対生成によってバルク材料全体に生成されるため、数センチメートルの厚い材料の欠陥分析が可能になる。(ii)密封線源の被覆材料で消滅した陽電子の寄与がないため、データ分析が簡単かつ正確になる。
芝田 悟朗
no journal, ,
Layered transition-metal dichalcogenides with the 1T-CdI-type crystal structure are known to exhibit a wide variety of electric and magnetic properties by intercalating various transition-metal atoms of different concentrations between adjacent layers. Among them, iron-intercalated titanium disulfides FeTiS and tantalum disulfides FeTaS are ferromagnets which exhibits strong perpendicular magnetic anisotropy (PMA) with large coercive fields of a few tesla. It is reported that FeTaS shows stronger PMA than FeTiS, presumably due to the stronger spin-orbit interaction (SOI) of Ta. In the present study, in order to elucidate the microscopic origin of the strong PMA in these compounds, the electronic structure and magnetism of single-crystalline FeTiS and FeTaS have been investigated via X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the spectral line shapes of XAS and XMCD, the valence of Fe is shown to be essentially 2+, whereas Ti is in an itinerant electronic state between 3+ and 4+. This shows that electrons are doped from the intercalated Fe atoms into the host TiS and TaS. Notably, clear differences in the spectral line shapes of XMCD at the Fe edges are observed between FeTiS and FeTaS despite the similarity of the crystal structures. This may be attributed to the different SOI strength between these compounds. Based on the configuration-interaction cluster-model calculations, the observed changes in the spectral line shapes can be qualitatively reproduced by virtually increasing SOI of Fe 3 electrons.