Regensburg 2013 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 40: Molecular Magnetism
MA 40.7: Vortrag
Donnerstag, 14. März 2013, 16:45–17:00, H23
Huge magnetically coupled orbital moments of Co porphyrin molecules and their control by CO adsorption — •Christian F. Hermanns1, Kartick Tarafder2, Matthias Bernien1, Alex Krüger1, Waldemar Walter1, Yin-Ming Chang1, Eugen Weschke3, Peter M. Oppeneer2, and Wolfgang Kuch1 — 1Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, 14195 Berlin, Germany — 2Department of Physics and Astronomy, Uppsala University, P.O. Box 516, 75120 Uppsala, Sweden — 3Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
We report on a combined experimental-theoretical study of physisorbed Co-porphyrin molecules on a graphene-protected Ni film. By using X-ray magnetic circular dichroism, we show that an antiferromagnetic coupling between the Co and Ni spins is established across graphene. According to density functional theory calculations the coupling is mediated via the π electronic system of graphene. The Co ions, despite their four-fold coordination, reveal a huge measured in-plane orbital moment ml, even comparable in size to the spin moment. Carbon monoxide adsorption on top of the molecules reduces the Co orbital moment by (77 ± 6)% and the entire magnetic moment by (37 ± 3)%, without modifying the spin state S=1/2. This is attributed to the change of the crystal field by the chemical stimulus, which determines ml together with the spin-orbit coupling.
This work is supported by the DFG (Sfb 658), the Swedish-Indian Research Link Programme, the C. Tryggers Foundation, and the SNIC.