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Observation of two charge ordering transitions in the valence-fluctuating EuPtP by resonant X-ray diffraction

共鳴X線回折を用いた価数揺動系EuPtPの二つの価数秩序転移の観測

稲見 俊哉; 道村 真司; 光田 暁弘*; 和田 裕文*

Inami, Toshiya; Michimura, Shinji; Mitsuda, Akihiro*; Wada, Hirofumi*

価数揺動物質EuPtPの$$T_1$$=246Kと$$T_2$$=200Kの二つの一次転移を、Euの$$L_3$$吸収端での共鳴X線回折法で研究した。以前のメスバウアー分光実験とX線回折実験から価数秩序が示唆されていたが、今回の実験における111反射と11$$frac{2}{3}$$反射の特徴的なエネルギースペクトルから、疑いなく2倍周期と3倍周期のEu価数の超構造が$$T_2$$以下と$$T_1$$$$T_2$$の間で存在することが示された。われわれは、さらに、EuPtPにおける価数秩序を説明する機構として、クーロン反発に代わる価数-格子結合を提案した。

Two first-order phase transitions of the valence-fluctuating compound EuPtP at $$T_1$$=246 K and $$T_2$$=200 K were examined by means of resonant X-ray diffraction at the Eu $$L_3$$ absorption edge. Although previous M$"o$ssbauer spectroscopy and preliminary X-ray diffraction experiments have suggested charge ordered states, characteristic energy spectra of the 111 and 11$$frac{2}{3}$$ reflections observed in the present experiment unambiguously indicated that twofold and threefold superstructures of Eu valence exist below $$T_2$$ and between $$T_1$$ and $$T_2$$, respectively. We also propose a mechanism to explain the charge ordering in EuPtP based on a charge-lattice coupling that alters a Coulomb repulsion.

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パーセンタイル:46.13

分野:Materials Science, Multidisciplinary

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