Applicability of the two-current model for systems with strongly spin-dependent disorder

The resistivities of the ferromagnetic alloy systems Fe-Ni and Co-Ni were studied in detail by application of first-principles techniques. For that purpose the Kubo-Greenwood formalism was applied on the basis of electronic structure data obtained using the spin-polarized Korringa-Kohn-Rostoker coherent potential approximation method of band-structure calculation for randomly disordered ferromagnetic alloys. One set of calculations was carried out fully relativistically, while for a second one the well-known and often applied two-current model was used. We compare the results of the two approaches as well as the difference between the calculated two-current resistivities and the resistivities obtained experimentally by the usual decomposition based on the two-current model. We discuss the validity of the two-current model for the systems investigated and the reason for the apparent success of this model.