Cu(1 1 1) supported graphene as a substrate for magnetic dimers with a large magnetic anisotropy: relativistic...

We report on our relativistic density-functional investigations of the properties of transition-metal dimers adsorbed on a graphene monolayer supported by a Cu(1 1 1) substrate, which extends our studies of dimers in the gas-phase and adsorbed on a freestanding graphene layer (Błoński and Hafner 2014 J. Phys.: Condens. Matter 26 146002). The presence of the Cu(1 1 1) substrate enhances the interaction between the dimer and the support. For homoatomic dimers such as Ir2 and Pt2 a flat adsorption geometry is now preferred over an upright geometry, which is stable on a graphene monolayer. The magnetic moment of the dimer is strongly reduced, the magnetic anisotropy is very low-in contrast to the strong anisotropy of free and graphene-supported Ir2 and Pt2 dimers. For heteroatomic IrCo and PtCo dimers the upright geometry with the Co atom located in a sixfold hollow of the graphene layer is preserved, but the stronger interaction with the support leads to a further enhancement of the large magnetic anisotropy energy of IrCo to 0.2 eV/dimer, while that of PtCo is reduced. The mechanism determining the magnetic anisotropy is discussed in relation to the electronic structure of the dimers.