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MA: Magnetismus
MA 5: Spin-Structures and Magnetic Phase Transitions I
MA 5.8: Talk
Monday, March 27, 2006, 12:00–12:15, HSZ 403
Orbital ordering and spin gap in ruthenate La4Ru2O10 — •Hua Wu1, T. Burnus1, Z. Hu1, J.D. Denlinger2, L.-Y. Jang3, H.H. Hsieh4, P.G. Khalifah5, F. Wang6, J.W. Allen6, K.S. Liang3, D.I. Khomskii1, and L.H. Tjeng1 — 1II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany — 2Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA — 3National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan — 4Chung Cheng Institute of Technology, National Defense University, Taoyuan 335, Taiwan — 5Department of Chemistry, University of Massachusetts, Amherst, MA 01003, USA — 6Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
It was discovered [P. Khalifah et al., Science 297, 2237 (2002)] that La4Ru2O10 undergoes a rare 4d-orbital ordering transition below 160 K and acquires a spin gap. We study this interesting orbital-ordered spin-gap state both by x-ray absorption spectroscopy measurements and by LDA+U band calculations. Our results show that the Ru4+ ions remain in the normal spin=1 state. A distinct orbital ordering is identified, which leads to a significant anisotropy of antiferromagnetic exchange couplings. As a result, the spin gap is opened due to formation of the Ru4+-Ru4+ spin-singlet dimers but not to the originally assumed spin-state transition. Thus, La4Ru2O10 appears to be a novel orbital-ordering-assisted spin-ladder material.