Berlin 2012 – scientific programme
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MA: Fachverband Magnetismus
MA 3: Bio- and Molecular Magnetism
MA 3.7: Talk
Monday, March 26, 2012, 11:15–11:30, EB 202
Magnetic coupling between metalloporphyrins and Ni films across a graphene sheet — •Christian Felix Hermanns1, Kartick Tarafder2, Mattias Bernien1, Alex Krüger1, Yin-Ming Chang1, Anton Bruch1, Peter Oppeneer2, and Wolfgang Kuch1 — 1Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany — 2Department of Physics and Astronomy, Uppsala University, P.O. Box 516, S-75120 Uppsala, Sweden
We report on a combined experimental-theoretical study of Co and Fe octaetylporphyrin (CoOEP and FeOEP) molecules on a graphene sheet, supported by a ferromagnetic (FM) Ni film on W(110). Consistent with the results of angle-dependent X-ray absorption spectroscopy (XAS) at the N K edge, density functional theory (DFT+U) calculations show that both, CoOEP and FeOEP molecules, adsorb flat on the surface, while the porphyrine macrocycles are distorted due to the interaction with the substrate. By means of X-ray magnetic circular dichroism measurements at the Co and Fe L2,3 edges we show that the FM Ni film induces a magnetic order on the Co and Fe ions of the porphyrins. According to DFT+U calculations the underlying mechanism is an indirect exchange coupling across the graphene layer. Angle dependent Co and Fe L2,3 XA spectra resemble those of free molecules, indicating a physisorption of the metalloporphyrins. This is in line with the calculated distances between the porphyrins and the graphene plane of more than 3 Å for both types of metalloporphyrins.
This work is supported by the DFG (Sfb 658), the Swedish-Indian Research Link Programme, the C. Tryggers Foundation, and the SNIC.