Regensburg 2010 – wissenschaftliches Programm

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KR: Fachverband Kristallographie

KR 10: Poster: Multiferroics (with MA, DF, KR, DS)

KR 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 Pinta^1,2, Andrei Samartsev^1,2, Markus Wissinger^1,2, Hilbert von Löhneysen^1,2, Andrea Assmann^1,2, Stephan Uebe^1,2, 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 L_2,3 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.