Electronic and magnetic properties of the graphene-ferromagnet interface

Abstract. The article presents the work on the investigation of the surface structure as well as electronic and magnetic properties of graphene layer on a lattice matched surface of a ferromagnetic material, Ni(111). Scanning tunneling microscopy imaging shows that perfectly ordered epitaxial graphene layers can be prepared by elevated temperature decomposition of hydrocarbons, with domains larger than the terraces of the underlying Ni(111). In some exceptional cases graphene films do not show rotational alignment with the metal surface leading to moire ́ structures with small periodicities. We give a detailed analysis of the crystallographic structure of graphene with respect to the Ni(111) surface based both on experimental results and recent theoretical studies. X-ray absorption spectroscopy investigations of empty valence band states demonstrate the existence of interface states which originate from the strong hybridization between the graphene pi and Ni 3d valence-band states with the partial charge transfer of the spin-polarized electrons to the graphene pi ∗ unoccupied states. The latter leads to the appearance of an induced magnetic moment of carbon atoms in the graphene layer which is unambiguously confirmed by both x-ray magnetic circular dichroism and spin-resolved photoemission. Further angle-resolved photoemission investigations indicate a strong interaction between graphene and Ni(111) showing considerable modification of the valence-band states of Ni and graphene due to a strong hybridization. The detailed analysis of the Fermi surface of the graphene/Ni(111) system show very good agreement between experimental and calculated two-dimensional maps of the electronic states around the Fermi level confirming the main predictions of the theory. We analyze our spectroscopic results relying on the currently available band structure calculations for the graphene/Ni(111) system and discuss the perspectives of the realization of graphene/ferromagnet-based devices