Energetics of 3d Impurities on the (001) Surface of Iron

Motivated by recent STM results for Cr on Fe(001) we present a detailed ab-initio study of the alloying process in the dilute limit for 3d atoms on the Fe(001) surface. The calculations are based on local density functional theory and apply a KKR{Green's function method for impurities on surfaces. For practically all 3d transition metal impurities on Fe(001) we nd a strong tendency for a direct exchange mechanism into the rst surface layer. The early 3d impurities V, Cr and Mn strongly repel each other on neighboring positions within the rst layer, while Ni and Cu atoms show a moderate repulsion. The ab{initio results are in good agreement with STM studies for Cr/Fe(001) by the NIST group and present valuable predictions for all 3d/Fe(001) systems. Over the last years experimental methods like ion eld and scanning tunneling microscopy became able to discern individual atoms on surfaces and to observe to a certain extent diiusion and formation processes on the surface of materials. Together with various cal-culational methods a good understanding of growth modes on an atomic scale has been achieved 1, 2]. The results so far suggest that adsorption and diiusion depend strongly on the combination of materials and that therefore no general rules can be applied. For a few substrate-adsorbate combinations the formation of surface alloys is found even though the adsorbates are principally immiscible in the substrate 3, 4]. In a recent STM study the growth and alloying of Chromium on the Fe(001) surface has been investigated 5]. The aim of this investigation was to understand a number of anomalies in the interlayer exchange coupling of Fe/Cr magnetic multilayers. The authors nd that under layer{by{ layer growth condition substantial alloying occurs at the Fe/Cr interface. For instance, 94