Spin polarization of graphene on Co2FeGe0.5Ga0.5(001) observed by spin-polarized surface positronium spectroscopy

Abstract

Following previous work on graphene on Ni(111) and Co(0001) surfaces [Phys. Rev. B 97, 195405 (2018)], the spin polarization of graphene on a ${\mathrm{Co}}_{2}{\mathrm{FeGe}}_{0.5}{\mathrm{Ga}}_{0.5}$ (CFGG) (001) surface was examined using spin-polarized surface positronium spectroscopy. The graphene was found to be magnetically insulated from the CFGG(001) even after heat treatment, which increased the spin polarizations of graphene on Ni(111) and Co(0001). First-principles calculations indicated that graphene is weakly bound to the CFGG(001) surface mainly through the van der Waals interaction, and consequently the interlayer distance between graphene and the CFGG(001) surface is greater ($\ensuremath{\sim}3$ \AA{}) than that between graphene and Ni(111) or Co(0001) ($\ensuremath{\sim}2$ \AA{}). The weak hybridization between graphene and CFGG(001) sufficiently reduces the spin polarization in graphene, which enables the magnetic insulation of graphene from CFGG.