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Complex Magnetic Exchange Coupling between Co Nanostructures and Ni(111) across Epitaxial Graphene

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journal contribution
posted on 2016-01-26, 00:00 authored by Alessandro Barla, Valerio Bellini, Stefano Rusponi, Paolo Ferriani, Marina Pivetta, Fabio Donati, François Patthey, Luca Persichetti, Sanjoy K. Mahatha, Marco Papagno, Cinthia Piamonteze, Simon Fichtner, Stefan Heinze, Pietro Gambardella, Harald Brune, Carlo Carbone
We report on the magnetic coupling between isolated Co atoms as well as small Co islands and Ni(111) mediated by an epitaxial graphene layer. X-ray magnetic circular dichroism and scanning tunneling microscopy combined with density functional theory calculations reveal that Co atoms occupy two distinct adsorption sites, with different magnetic coupling to the underlying Ni(111) surface. We further report a transition from an antiferromagnetic to a ferromagnetic coupling with increasing Co cluster size. Our results highlight the extreme sensitivity of the exchange interaction mediated by graphene to the adsorption site and to the in-plane coordination of the magnetic atoms.