Calculated surface electronic structure of ferromagnetic iron and the ferromagnetic ordered iron-cobalt alloy

The electronic and magnetic properties of the (100) and (110) surfaces of ferromagnetic iron and the ferromagnetic iron-cobalt ordered alloys are calculated self-consistently. It is found that (a) in pure bcc iron the spin polarization increases from a bulk value of 2.12 to 2.90 at the (100) surface and to 2.55 at the (110) surface; (b) the ordered FeCo alloy has a bulk spin polarization of 2.66 for the Fe constituent and 1.78 for the Co constituent, compared with 2.12 and 1.56 for the respective pure elements; (c) in the (100) surfaces of ordered FeCo, the spin polarizations are 2.95 for Fe and 2.03 for Co; (d) the (110) surface of ordered FeCo exhibits spin polarizations of 2.75 for Fe and 1.86 for Co; (e) an atomic (110) overlayer of Fe on ordered FeCo produces a surface spin polarization of 2.63 and 2.67 for the two inequivalent Fe atoms. Agreement with available experimental data is excellent. All results can be successfully interpreted based on the saturation magnetization of Co, the relatively weak electron-electron interaction of Fe, and the surface narrowing of the electronic $d$ band.