Cobalt multilayers on diamond surfaces: An ab-initio study

Stärk B, Krüger P, Pollmann J

Zusammenfassung

Structural, electronic, and magnetic properties of particular metal-semiconductor hybrid systems are investigated employing spin-density-functional theory within generalized gradient approximation. They consist of one up to six monolayers of cobalt on (111) and (001) surfaces of diamond and are characterized by a very small lattice mismatch of the constituents. For monolayer coverage, the Co atoms adsorb in on top sites on the C(111) surface while they adsorb in symmetric bridge sites on the C(001) surface. Strong covalent bonds are formed between the Co3d and C2p orbitals which saturate all surface dangling bonds in each case. The pd bonds give rise to characteristic bonding and antibonding bands which exhibit no significant spin splitting. As a result, the magnetic moment of the Co atoms on the interface layer is considerably quenched. The magnetic moment of 0.96μB per Co atom for one Co adlayer on C(111) turns out to be strongly reduced with respect to 1.76μB for the top layer atoms of a Co(0001) surface or 1.87μB for a free-standing hexagonal Co monolayer. Further Co adlayers lead to an increase in the magnetization rapidly approaching 1.19μB at the Co interface and 1.77μB at the Co surface layer. For one Co adlayer on C(001), where each Co atom forms two pd bonds with the substrate, the magnetic moment per Co atom is even reduced to 0.42μB, as compared to 1.92μB for the top layer atoms of a Co(001) surface or 2.05μB for a free-standing cubic Co monolayer. For six Co adlayers on C(001) the magnetic moment turns out to be 0.91μB at the interface and 1.92μB at the surface layer. For both types of hybrid systems the spin polarization at the Co-C interface depends sensitively on the number of Co adlayers. For several systems it amounts to about 60% at the Fermi level.