Spin-polarized hybrid states in epitaxially-aligned and rotated graphene on cobalt

The strong interaction between graphene and elemental ferromagnetic transition metals results in considerable shifts of the graphene pi band away from the Fermi level. At the same time, a weakly-dispersing single-spin conical band feature is found in the proximity of the Fermi level at the (K) over bar point in the surface Brillouin zone of epitaxially-aligned graphene/Co(0001). Here, the robustness of this electronic state against twisting angles at the interface is experimentally and theoretically demonstrated by showing the presence of similar band features also in the case of rotated graphene domains on Co(0001). Spin-resolved reciprocal space maps show that the band feature in rotated graphene has similar Fermi velocity and spin polarization as its counterpart in epitaxially-aligned graphene. Density functional theory simulations carried out for the experimentally observed graphene orientations, reproduce the highly spin-polarized conical band feature at the graphene K point, characterized by a hybrid pi-d orbital character. The presence of the conical features in the rotated domains is attributed to the unfolding of the superstructure K point states exclusively to the K point of the graphene primitive cell. The similarities found in the electronic character for different graphene orientations are crucial in understanding the magnetic properties of realistic graphene/Co interfaces, facilitating their implementation in spintronics applications.