Segregation of Cr impurities at bcc iron surfaces: First-principles calculations

The segregation of Cr impurities placed in different layers at four low-index iron surfaces is studied from first principles in the dilute limit of Cr concentration. The surface segregation depends strongly on the surface orientation. For a single Cr atom in the computational cell, configurations with Cr atom in the outer surface layers are found to be unfavorable. However, for higher bulk Cr concentration, the Cr-enriched surfaces are predicted. The magnetic moment on the Cr-solute atoms in surface layers is much increased and follows the trend observed for the Fe-host atoms.