Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 33: CE: Metal-Insulator Transition 1
TT 33.2: Vortrag
Mittwoch, 16. März 2011, 10:45–11:00, HSZ 105
Symmetry of magnetite in the low-temperature phase — •Chun-Fu Chang1, Arata Tanaka2, Marcel Buchholz1, Christoph Trabant1,3, Enrico Schierle3, Justina Schlappa3, Detlef Schmitz3, Marita Döhler1, Pascal Vogt1, Liu Hao Tjeng1,4, and Christian Schüßler-Langeheine1,3 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Department of Quantum Matter, ADSM, Hiroshima University, Japan — 3Helmholtz-Zentrum Berlin, Germany — 4Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
Magnetite (Fe3O4) undergoes upon cooling below 123 K a first order phase transition, which is accompanied by a rise of the resistivity by two orders of magnitude: the Verwey transition. Below the transition, magnetite exhibits a complex crystal structure; structural studies so far assume a pseudo orthorhombic symmetry. We have carried out a combined experimental and theoretical analysis of the local symmetry of the divalent iron ions in octahedral environment in magnetite. Our results clearly show that the local symmetry of these iron ions cannot be described as pseudo-orthorhombic. A monoclinic distortion is not a small correction but dominant. This has important consequences for the kind of orbital order that can form in magnetite. The orbital-order models based on the pseudo-orthorhombic symmetry are hence challenged. On the other hand a model assuming a complex orbital order matches the experimental data very well. Supported by the DFG through SFB 608, by the BMBF through projects 05 S3XBA/5 and 05 KS7PK1, and by the HZB.