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TT: Tiefe Temperaturen

TT 25: Correlated Electrons - Poster Session

TT 25.96: Poster

Mittwoch, 29. März 2006, 14:30–18:30, P1

Valence and spin state in Ca₃FeRhO₆ and Ca₃CoRhO₆ studied by XAS — •Zhiwei Hu¹, Tobias Burnus¹, Seiji Niitaka², Chun-Fu Chang¹, Hua Wu¹, Júlio Criginski Ceszar³, Nicholas B. Brookes³, Ling-Yun Jang⁴, Hong-Ji Lin⁴, Hidenori Takagi², Keng San Liang⁴, Chen Te Chen⁴, and Liu Hao Tjeng¹ — ¹II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln — ²Magnetic Material Laboratory, RIKEN (Institute of Physical and Chemical Research), Wako 351-0198, Japan — ³European Synchrotron Radiation Facility, BP 220, Grenoble 38043, France — ⁴National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan

The physical properties of triangular-lattice systems has been attracting much interest because the geometrical frustration produces novel types of phase transitions. The triangular lattice in Ca₃CoRhO₆ and Ca₃FeRhO₆ consist of one-dimensional chains with faced-sharing CoO₆ and FeO₆ trigonal prisms and of RhO₆ octahedra. Neutron diffraction experiments indicate ferromagnetic Ising-spin chains in Ca₃CoRhO₆ and a three-dimensional antiferromagnetic transition at 12 K in CaFeRhO₆. The valence and spin states in both compounds are a matter of controversy. The combined experimental and theoretical X-ray absorption spectroscopy (XAS) study at the Co-, Fe- and Ru-L_2,3 edges presents unambiguously Co²⁺/Rh⁴⁺ and Fe³⁺/Rh⁴⁺ states in Ca₃CoRhO₆ and CaFeRhO₆, respectively. The X-ray magnetic circular dichroism at the Co-L_2,3 edge indicates a large orbital moment of Co²⁺ in Ca₃CoRhO₆.