Regensburg 2013 – scientific programme

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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.