Magnetic properties of small Pt-capped Fe, Co, and Ni clusters: A density functional theory study

We have undertaken theoretical studies of spin and orbital magnetic moments as well as magnetic anisotropy energies for M-13 (M = Fe, Co, Ni) and M13Ptn (n = 3,4,5,20) clusters including the spin-orbit coupling in the framework of density functional theory. For all M-13 clusters considered we find tendencies for small structural distortions which can be characterized by either Jahn-Teller (JT) or Mackay transformations (MT). The magnetic anisotropy energy (MAE) along with the spin and orbital moments are calculated for M-13 icosahedral clusters and the angle-dependent energy differences are modeled using a Neel model with local anisotropies. From our studies, the MAE for JT-distorted M-13 clusters are found to be larger relative to the MT clusters and more than two orders of magnitude larger compared to the corresponding bcc or fcc bulk values. In addition, we demonstrate for one example that Pt capping may further enhance the MAE compared to the uncapped JT- and the Mackay-distorted Fe-13 cluster.