Electronic structure and surface magnetism of fcc Co(001)

A full potential linearized augmented plane wave (FLAPW) all-electron local spin density calculation of the electronic and magnetic properties of both five and nine layer fcc Co(001) ferromagnetic films is reported. The surface magnetic moment of 1.85μ_B is 13% larger than that of the bulk value as a result of the narrowing of the 3d band at the surface. The effects of the surface is found to be short-ranged, with changes in charge and spin densities localized mostly to the surface layer. The sub-surface Co atom layers have magnetic moments equal to 1.64μ_B, i.e., a value very close to that of bulk fcc Co, indicating a short range effect of the surface on the magnetism (i.e., one atomic layer screening length). A contact magnetic hyperfine field calculation indicates that the core electron contribution is, as usual, precisely proportional to the magnetic moment, while the valence electron contribution is rather sensitive to the atomic environment. The total energy results yield a surface energy for the fcc Co(001) surface equal to 4.1 J/m².