Atomic-scale observations of alloying at the Cr-Fe(001) interface.

While much progress has been made using epitaxial growth of Fe/Cr/Fe structures to study magnetic exchange coupling, a number of anomalies have arisen in studies of this model system. Using scanning tunneling microscopy and spectroscopy to investigate Cr growth on Fe(001), we have identified a potential structural cause of these anomalies. We show that Cr growth under layer-by-layer conditions on Fe(001) leads to the formation of a Cr-Fe alloy. We exploit a Cr and Fe surface state to identify single Cr impurities in Fe and evaluate the alloy concentrations with increasing Cr coverage. PACS numbers: 61.16.Ch, 68.55.-a, 75.70.Cn