Transition metal adatom and dimer adsorbed on graphene: Induced magnetization and electronic structures

Geometries, electronic structures, and magnetic properties of transition metal M adatom and dimer adsorbed graphene have been studied (M=Fe, Co, Ni, and Cu). With adatom adsorption, we confirm the previously reported stable adsorption site, and the adatoms are chemically bonded with graphene except the copper adatom. With dimer adsorption, we observed that the stable configurations are dependent on the exchange-correlation functional for the iron dimer and nickel dimer; while the stable configurations do not depend on the functional for the cobalt and copper dimer. The adsorption energy indicates the copper dimer can barrierlessly diffuse along the graphene C-C bonds. With iron or cobalt adatom adsorption, graphene becomes a half-metal which can be used as a spin-filtering material. The iron dimer adsorbed graphene is also a half-metal, but the cobalt dimer adsorbed graphene is not. Both local-density approximation and generalized gradient approximation yield consistent results for the nickel adatom adsorbed graphene, which is the system is semiconducting and nonmagnetic due to the strong binding between nickel and graphene. However, different exchange-correlation functionals lead to controversial results for the magnetic and transport properties of nickel dimer adsorbed graphene. The copper adatom adsorbed on graphene exhibits 1 mu(B) local magnetic moment, but the dimer does not show any magnetism. These results show that graphene properties can be effectively modulated by transition metal adsorption and that the transition metal adsorbed graphene can serve as potential materials in nanoelectronics, spintronics, or electrochemistry.