Regensburg 2010 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 10: Poster I
MA 10.54: Poster
Dienstag, 23. März 2010, 10:45–13:45, Poster A
Soft x-ray magnetic dichroism of undoped, hole-doped and electron-doped LaCoO3: Anisotropies and valence-dependent magnetism — •Michael Merz1, Christian Pinta1,2, Andrei Samartsev1,2, Markus Wissinger1,2, Hilbert von Löhneysen1,2, Andrea Assmann1,2, Stephan Uebe1,2, Dirk Fuchs1, Peter Nagel1, and Stefan Schuppler1 — 1Karlsruhe Institute of Technology, Institut für Festkörperphysik, Germany — 2Karlsruhe Institute of Technology, Physikalisches Institut, Germany
Epitaxial thin films of undoped LaCoO3, of electron-doped (La,Ce)CoO3, and of hole-doped (La,Sr)CoO3 exhibit ferromagnetic order with optimum transition temperatures of 80 K, 30 K, and 240 K, respectively. The spin-state structure for these compounds was studied by soft x-ray absorption and magnetic circular dichroism at the Co L2,3 and O K edges. It turns out that for epitaxial LaCoO3, strain imposed by the substrate preserves a higher spin state of the Co3+ ions at low temperature and prevents a non-magnetic ground state. For (La,Ce)CoO3, the Co3+ ions are predominantly in a low-spin (S = 0) state and thus magnetically inactive, and the ferromagnetism is determined by the Co2+ species. For (La,Sr)CoO3, on the other hand, the magnetism originates from higher spin states of Co3+ (S = 2) and Co4+ (S = 3/2) ions. The data show that ferromagnetism has a different origin in LaCoO3 (superexchange), (La,Ce)CoO3 (spin blockade), and (La,Sr)CoO3 (double exchange). Moreover, a strong magnetic anisotropy is observed for all systems, with the spin and the orbital moments essentially lying within the substrate plane.
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