Magnetic properties of Fe2n and (FePt)n(n≤5) clusters and magnetic anisotropy of transition metal dimers

Structures and magnetic properties of (FePt)n clusters (with n≤5) have been studied within density functional theory (DFT). Specific attention has been paid to the influence of the spin-orbit interaction on the geometry, binding energy and magnetic moments. It is found that for (FePt)n clusters, the ground states usually display collinear magnetic behavior, although small deviations from the collinear direction are noticeable when the spin-orbit interaction (SOI) is included. The spin magnetic moment and the binding energy increase with the size of the cluster, although the spin magnetic moment per (FePt) unit remains unaltered. The spin magnetic moment of the Pt atoms slightly increases with the cluster size. The orbital and spin magnetic moments of Fe atoms increases when Fe is alloyed to Pt atoms, larger than that is obtained in pure iron clusters and shrinks with cluster size. For the dimers studied, a large magnetic anisotropy energy (MAE) is observed for Pt2, Co2 and CoPt with a large orbital magnetic moment in the ground state(easy axis). In other way, we note the dependence of MAE on the orbital magnetic anisotropy. In contrast for Fe2 and FePt, the MAE is relatively small.