Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 34: Correlated Electrons: Metal-Insulator Transition 2
TT 34.13: Vortrag
Donnerstag, 28. Februar 2008, 17:30–17:45, H 2053
Crystal Structure of layered manganites — •Olaf Schumann1, Stephen Price1, Hua Wu1, Theresa Fernandez-Diaz2, Pascal Reutler3, Alexandre Revcolevschi3, and Markus Braden1 — 1II. Phys. Institut; Universität zu Köln, Zülpicher Straße 77, 50937 Köln — 2ILL, Grenoble, France — 3LPCES, Paris Orsay, France
Manganites in a perowskite structure have attracted strong attention during the past years, mainly because of the discovery of the colossal magneto resistivity effect (CMR) and complex charge, orbital and magnetic ordering phenomena. Because of the twining in the perowskites, precise structural investigations to determine the ordering pattern are hampered. Therefore we investigated the single-layer manganites, which show similar ordering phenomena but only small magneto-resistivity effects. Since these materials are not intrinsically twinned, structure determination can be performed with much higher precision. For the ordered phase of half-doped manganites, two models were proposed, the Zener polaron model with bond-centered charge ordering and the so called CE-type model with size centered charge and orbital order, leading to two different Mn-sites. We present the results of powder and single crystal diffraction studies on La0.5Sr1.5MnO4. From a neutron diffraction study on the D10 diffractometer and several x-ray diffraction experiment on our home diffractometer we can unambigously distinct between the two proposed models. The Zener-polaron model does not yield a satisfying description of the observed intensities. Details of the the ordered structure in the CE-Type model will be discussed.