Magnetic doping of 4d transition-metal surfaces: A first-principles study

The doping of 4d transition-metal surfaces by magnetic 3d impurities is studied on the example of Co/Rh(111) in the framework of the density functional theory, in its generalized gradient approximation and within the projector-augmented plane-wave method. Full Co monolayers buried close to a free surface in a Rh matrix as well as surface alloys for varying Co concentrations are considered. The magnetic impurities are shown to essentially maintain a bulk-enhanced magnetic moment, even at small concentration. They induce a long-range oscillatory decaying polarization of the Rh adjacent layers whose amplitude is significantly enhanced at the surface. This behavior leads to a complex magnetic pattern of the surface alloys. Co is preferentially accommodated in the subsurface layer and induces substantial magnetic moments on the Rh surface atoms which increase linearly with the local Co coordination and leads to giant effective moments of more than 4?B for low Co coverage. For less stable Co positions, antiparallel induced Rh moments may reduce the total effective moment. Our findings are discussed within the framework of the band theory of magnetism. Œ2005 The American Physical Society.