Spin-polarized field emission from Ni(001) and Ni(111) surfaces

Results are presented of a first-principles calculation of the spin-polarized field emission from ferromagnetic Ni(111) and Ni(001) surfaces. The electronic structure of both surfaces exposed to an external field is determined by combining the surface-embedded Green function approach and the full-potential linearized augmented plane-wave (FLAPW) method within the local spin density approximation. We discuss the contributions of different states to the field-emission current. In particular, we show that delocalized states make similar contributions to that obtained at jellium surfaces while localized Ni d states contribute mostly through surface states and resonances. These contributions dominate in the minority spin and lead to a negative spin polarization of the emitted current.