THEORY OF MAGNETORESISTANCE IN CONCENTRATED FERROMAGNETIC-ALLOYS (INVITED)

Existing values of the magnetoresistance (ρ∥- ρ⊥)/ρ0 for crystalline Ni 1-xFex, Ni1-xCox, Ni 1-xMnx, Fe1-xCrx, and Fe 1-x-Vx alloys depend on x in a way which disagrees with the traditional Smit theory, based on the Born approximation. The reasons are related to the variation of the 3d wave-function amplitude between chemically different atoms and, in turn, to a variation of s-d scattering intensity. Experimental atomic moments indicate that this 3d amplitude variation is large. The variation is related to the fact that d-d scattering is strong and resonant. We predict large deviations from Nordheim's rule ρ↓∝ x(1-x) where ρ↓ is the spin-down resistivity, similar to the deviations found experimentally. Correspondingly, (ρ∥- ρ⊥)/ρ0 is much larger for x≅0 than for x≅1.