Hydrogen-induced reversal of spin alignment in graphene supported on Ni(111) surface

We present a chemical way of changing the alignment of the induced magnetic moment of graphene supported on a Ni(111) surface through hydrogenation. For the pristine graphene on a Ni(111) surface, the magnetic moments on the fcc (top) C atoms are parallel (antiparallel) with respect to those of the Ni atoms. The graphene sheet becomes ferrimagnetic with the average magnetic moment of the graphene sheet parallel with respect to that of the Ni atoms of the substrate. Our density functional theory based study shows that this alignment can be controlled by gradually hydrogenating the supported graphene layer. At maximum H coverage (0.5 monolayer), we find the supported hydrogenated graphene to be a ferromagnetic semiconductor, the average magnetic moment of the graphene sheet is antiparallel with respect to the Ni atoms. We attribute this chemically induced spin alignment transition to the quenching of the magnetic moment of the fcc-C atoms when H binds to them. Preliminary studies suggest that the hydrogenated graphene sheet can act as a tunneling barrier for magnetic tunnel junctions.