Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 32: Correlated Electrons: Poster Session

TT 32.30: Poster

Thursday, February 28, 2008, 14:00–18:00, Poster B

Electric and magnetic Properties of the Kagomé Systems YBaCo₄O_7+δ and YBaCo₃MO₇ (M=Fe,Al) — •Nils Hollmann¹, Martin Valldor¹, Zhiwei Hu¹, Antoine Maignan², Joachim Hemberger¹, Arata Tanaka³, Liu Hao Tjeng¹, Thomas Lorenz¹, and John Mydosh¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²Labaratoire CRISMAT, Caen — ³Department of Quantum Matter, Hiroshima University

YBaCo₄O_7+δ, YBaCo₃FeO₇ and YBaCo₃AlO₇ are closely related systems with cobalt ions in kagomé layers. In these kagomé layers, the triangular arrangement of the cobalt ions gives rise to a high degree of magnetic frustration. YBaCo₄O₇ reversibly changes the oxygen content depending on temperature and oxygen pressure. We present a study of magnetization, electrical transport and X-ray absorption of these materials. The systems are insulators and the electrical resistivity shows an anisotropy. The temperature dependence of the magnetization shows signs of strong frustration and spin-glass-like behaviour. This is studied with both DC and AC magnetization measurements. With the help of polarization dependent X-ray absorption, we deduce the valency and the orbital occupation of the cobalt ions. The valencies found can be used to prove the oxygen stochiometry.