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MA: Fachverband Magnetismus
MA 63: Poster II (Surface Magnetism/ Magnetic Imaging/ Topological Insulators/ Spin Structures and Magnetic Phase Transitions/ Graphene/ Magnetic Thin Films/ Magnetic Semiconductors/ Magnetic Half-metals and Oxides/ Spin-dependent Transport/ Spin Excitations and Spin Torque/ Spin Injection and Spin Currents in Heterostructures/ Spintronics/ Magnetic Storage and Applications)
MA 63.23: Poster
Freitag, 18. März 2011, 11:00–14:00, P2
X-ray absorption and magnetic circular dichroism of LaCoO3, La0.7Ce0.3CoO3, and La0.7Sr0.3CoO3 films: Evidence for Co valency-dependent magnetism — •Michael Merz1, Peter Nagel1, Andrea Assmann1,2, Stephan Uebe1,2, Markus Wissinger1,2, Hilbert von Löhneysen1,3, Dirk Fuchs1, and Stefan Schuppler1 — 1Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany — 2Fakultät für Physik, Karlsruhe Institute of Technology, 76031 Karlsruhe, Germany — 3Physikalisches Institut, Karlsruhe Institute of Technology, 76031 Karlsruhe, Germany
Epitaxial thin films of undoped LaCoO3, of electron-doped La0.7Ce0.3CoO3, and of hole-doped La0.7Sr0.3CoO3 exhibit ferromagnetic order with a transition temperature TC ≈ 84 K, 23 K, and 194 K, respectively. The spin-state structure for these compounds was studied by soft x-ray magnetic circular dichroism and by near-edge x-ray absorption fine structure at the Co L2,3 and O K edges. It turns out that superexchange between Co3+ high-spin and Co3+ low-spin states is responsible for the ferromagnetism in LaCoO3. For La0.7Ce0.3CoO3 a spin blockade between Co3+ low-spin and Co2+ high-spin ions naturally explains the low transition temperature and the insulating characteristics of La0.7Ce0.3CoO3. For La0.7Sr0.3CoO3, ferromagnetism and metallicity is induced by t2g double exchange between Co3+ and Co4+ high-spin states. For all systems, a strong magnetic anisotropy is observed, with the magnetic moments essentially oriented within the film plane.