Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: Correlated Electrons: Metal-Insulator Transition 2

TT 34.12: Talk

Thursday, February 28, 2008, 17:00–17:15, H 2053

X-ray absorption and x-ray magnetic dichroism study on Ca₃CoRhO₆ and Ca₃FeRhO₆ — •Tobias Burnus¹, Zhiwei Hu¹, Júlio C. Cezar², Seiji Niitaka³, Hua Wu¹, Hidenori Takagi^3,4, Chun Fu Chang¹, Nicholas B. Brookes², Ling-Yun Jang⁵, Keng S. Liang⁵, and L. Hao Tjeng¹ — ¹II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln — ²European Synchrotron Radiation Facility, Grenoble, France — ³RIKEN and CREST, Saitama, Japan — ⁴University of Tokyo, Japan — ⁵National Synchrotron Research Center, Hsinchu, Taiwan

The valence-state of the transition-metal ions in the chain-like compounds Ca₃CoRhO₆ and Ca₃FeRhO₆ is currently an issue under debate. Using numerical simulations and x-ray absorption spectroscopy at the Rh-L_2,3, the Co-L_2,3, and the Fe-L_2,3 edges we reveal a Co²⁺/Rh⁴⁺ configuration in Ca₃CoRhO₆ and Fe³⁺/Rh³⁺ in Ca₃FeRhO₆. X-ray magnetic circular dichroism at the Co-L_2,3 edge shows that the Co²⁺ ions carry a giant orbital moment of about 1.7µ_B. We attribute this to a d₀¹d₂¹ ground state for the high-spin Co 3d⁷ configuration in trigonal prismatic coordination. The intrachain-ferromagnetic coupling of two neighboring Co ions is mediated by a low-spin Rh⁴⁺ ion (S = 1/2) in between.