▎ 摘　　要

We have performed first-principles calculation to investigate the magnetic exchange interactions of 3-D transition metals (TMs) adatoms on graphene. Our study found that the most stable adsorption sites and geometries of different 3-D TM dimmer adatoms on graphene are obviously distinct. The obtained magnetic exchange energies indicate that Fe and Co adatoms on graphenes are always ferromagnetic coupling. Thus, they may be a candidate of graphene-based spintronics devices. Furthermore, electronic structure analysis shows that mechanism of ferromagnetic interaction of 3-D TMs adatoms on graphene is either direct exchange (two TMs adatoms are on the same side of graphene) or superexchange (two TMs adatoms are on the two sides of graphene).