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O: Fachverband Oberflächenphysik
O 40: Spin Effects in Molecules at Surfaces (jointly with DS, MA)
O 40.10: Talk
Wednesday, March 13, 2013, 12:00–12:15, H23
Beyond the Heisenberg model: Anisotropic exchange interaction between a Cu-tetraazaporphyrin monolayer and Fe3O4(100) — •Hans-Joachim Elmers1, Julia Klanke2, Eva Rentschler2, Katerina Medjanik1, Dmytro Kutnyakhov1, Gerd Schönhense1, Sergey A. Krasnikov3, Igor V. Shvets3, Stefan Schuppler4, Peter Nagel4, and Michael Merz4 — 1Institut für Physik, Johannes Gutenberg-Universität Mainz, D-55128 Mainz, Germany — 2Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität Mainz, D-55099 Mainz, Germany — 3Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) — 4Karlsruhe Institute of Technology, Institut für Festkörperphysik (IFP), D-76021 Karlsruhe, Germany
We investigated the Heisenberg exchange coupling between the single Cu spin of Cu-tetraazaporphyrin deposited on magnetite(100) and the ferromagnetic surface using x-ray magnetic circular dichroism (XMCD). In contrast to the common model we find an anisotropic exchange coupling depending on the orientation of the spin relative to the bonding direction. The exchange coupling is ferromagnetic for magnetization direction perpendicular to the surface and antiferromagnetic for in-plane magnetization direction. The anisotropy of the Heisenberg exchange coupling is attributed to an orbitally-dependent exchange Hamiltonian. We propose that the sign change results from the competition between ferromagnetic superexchange along Fe-N-Cu and antiferromagnetic superexchange along Fe-O-Cu with strength modified by the strong spin-orbit coupling. Funded by COMATT.