Theoretical investigation of interface atomic structure of graphene on NiFe alloy substrate

The implementation of graphene as tunnel barriers in tunneling magnetoresistance devices attracts attention. So far, two processes have been proposed to fabricate graphene/NiFe alloy interfaces. One is the transfer of graphene and the other is the evaporation of alloys onto graphene. The formation energy of a NiFe alloy substrate and the adsorption energy of graphene on the NiFe alloy substrate are investigated by density functional theory calculations to reveal the difference in the atomic structure of the interface between the two processes. In the case of a bare substrate, Ni-rich surfaces are preferable regardless of composition of substrates. Interestingly, for the graphene adsorbed substrates, Fe-rich surfaces are stable due to the hybridization of a pz orbital of a C atom and a dz2 orbital of an Fe atom. This result indicates that the Ni-rich (Fe-rich) interface is formed by the graphene-transfer process (the alloy-evaporation process), and the composition ratio of the surface layer of graphene/NiFe alloy interfaces is significantly affected and controlled by the fabrication process.