Spin polarization of graphene and h−BN on Co(0001) and Ni(111) observed by spin-polarized surface positronium spectroscopy

In spin-polarized surface positronium annihilation measurements, the spin polarizations of graphene and $h$-BN on Co(0001) were higher than those on Ni(111), while no significant differences were seen between graphene and $h$-BN on the same metal. The obtained spin polarizations agreed with those expected from first-principles calculations considering the positron wave function and the electron density of states from the first surface layer to the vacuum region. The higher spin polarizations of graphene and $h$-BN on Co(0001) as compared to Ni(111) simply reflect the spin polarizations of these metals. The comparable spin polarizations of graphene and $h$-BN on the same metal are attributed to the creation of similar electronic states due to the strong influence of the metals: the Dirac cone of graphene and the band gap of $h$-BN disappear as a consequence of $d\ensuremath{-}\ensuremath{\pi}$ hybridization.