Nucleation, Structure and Magnetism of Transition Metal Clusters from First Principles
Properties of transition metal (TM) clusters such as structural stability, growth and magnetic properties are studied using the density functional theory (DFT). We find that for both elemental and binary clusters, different morphologies are stable for different ranges of cluster sizes. We discuss possible structural transformations namely Jahn-Teller (JT) and Mackay transformation (MT) occurring in TM clusters. While the JT-distorted cluster is stable for a Fe13 icosahedron, the MT-distorted structure is stable for Co13. For Ni13, however, both distortions lead to similar energies. In larger clusters, both JT and MT compete with each other, and as a result we find a higher stability for large Fe clusters with a shell wise Mackay transformation. Studies on binary Fe-Pt clusters show a segregation tendency of Pt atoms to the surfaces of the clusters. The ordered Fe-Pt icosahedral structures show enhanced stability compared to the L10 cuboctahedron. From the studies on magnetocrystalline anisotropy (MAE) for clusters, we find that relaxed Fe13 and Ni13 have several orders of magnitude larger MAE as compared to the corresponding bulk values. However, Co13 does not follow this trend.
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