Dresden 2011 – wissenschaftliches Programm

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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, La_0.7Ce_0.3CoO₃, and La_0.7Sr_0.3CoO₃ films: Evidence for Co valency-dependent magnetism — •Michael Merz¹, Peter Nagel¹, Andrea Assmann^1,2, Stephan Uebe^1,2, Markus Wissinger^1,2, Hilbert von Löhneysen^1,3, 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 La_0.7Ce_0.3CoO₃, and of hole-doped La_0.7Sr_0.3CoO₃ exhibit ferromagnetic order with a transition temperature T_C ≈ 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 L_2,3 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 La_0.7Ce_0.3CoO₃ a spin blockade between Co³⁺ low-spin and Co²⁺ high-spin ions naturally explains the low transition temperature and the insulating characteristics of La_0.7Ce_0.3CoO₃. For La_0.7Sr_0.3CoO₃, ferromagnetism and metallicity is induced by t_2g 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.