Electronic Structures and Magnetic Anisotropy Energies of Graphene with Adsorbed Transition-Metal Adatoms

We investigate the electronic structures of graphene with an adsorbed Fe, Co, or Ni adatom in the presence of spin-orbit coupling by density functional theory calculations. As a result of spin-orbit coupling, energy gaps are opened at the crossing points of spin-up and spin-down bands near the Dirac point in the cases of Fe and Co adatoms. In the case of the Ni adatom, the Rashba effect is observed with a k-dependent energy shift of the 3 bands at the bottom of the Fermi surface. The calculated magnetic anisotropy energies reveal that the Fe adatom exhibits an in-plane easy magnetization axis, while the Co adatom exhibits an out-of-plane easy axis.