We present ab-initio calculations of the magnetic moments and magnetic anisotropy energies of small FeCo clusters of varying composition on top of a Cu(100) substrate. Three different cluster layouts have been considered, namely 2x2, 3x3 and cross-like pentamer clusters. The ratio of Co atoms with respect to the total number in a chosen cluster (``concentration) was varied and all possible arrangements of the atomic species were taken into account. Calculations have been performed fully relativistically using the embedded cluster technique in conjunction with the screened Korringa-Kohn-Rostoker method and the magnetocrysergy depend on the position they occupy in a particular cluster and on the type and the number of nearest-neighbors. The MAE for the 2x2 and 3x3 clusters varies with respect to the ``concentration of Co atoms in the same manner as the corresponding monolayer case, whereas the pentamer clusters show a slightly different behavior. Furthermore, for the clusters with an easy axis along a direction in the surface plane, the MAE shows a significant angular dependence.
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