Tuning the magnetic anisotropy energy by external electric fields of CoPt dimers deposited on graphene

In the framework of first-principles calculations, we comprehensively investigate the external electric-field (EF) manipulation of the magnetic anisotropy energy (MAE) of alloyed CoPt dimers deposited on graphene. In particular, we focus on the possibility of tuning the MAE barriers under the action of external EFs and on the effects of Co-substitution. Among the various considered structures, the lowest-energy configurations were the hollow-upright and top-upright, having the Co-atom closest to the graphene layer. The optimal and higher energy configurations were related to the electronic structure through the local density of states and hybridizations between the transition-metal (TM) atoms of the dimer and graphene. In contrast to Co₂/graphene [M. Tanveer, J. Dorantes-Dávila and G. M. Pastor, Phys. Rev. B, 2017, 96(22), 224413.], the CoPt dimer having the hollow-upright ground-state configuration, exhibits a much lower value of the MAE (about |ΔE| ≃ 4.5 meV per atom) and the direction of the magnetization lies in the graphene layer. Moreover, we observe a spin-reorientation transition occurring at ε ≃ 0.5 V Å^-1, which opens the possibility of inducing magnetization switching by external electric fields. The microscopic origin of the changes of the MAE associated with changes in the EF has been qualitatively related to the details of the electronic structure by analyzing the local density of states and to the spin-dependent electronic densities close to the Fermi energy. Finally, the role of local environment was quantified by performing electronic structure and magnetic calculations on several higher-energy structure configurations.