On the temperature dependence of the magnetoresistance of ferromagnetic alloys

Abstract

The ferromagnetic anisotropy of resistivity Δρ/ρ0=(ρ∥−ρ⊥)/ρ0 depends strongly on the nature of the dominant electron scattering centers, and is usually larger for impurity scattering than for phonon scattering. This explains why Δρ/ρ0 decreases with increasing temperature T in crystalline transition-metal alloys. Parker has proposed an expression for Δρ/ρ0 as a function of T, based on Matthiessen’s rule. It contains the parameters (Δρ/ρ0)im and (Δρ/ρ0)ph, representing the Δρ/ρ0 values for impurity scattering and phonon scattering, respectively. In an alloy series with weak electron scattering, such as Fe-Co, (Δρ/ρ0)ph is found experimentally to be positive and equal to a fixed fraction ≂ (1)/(4) of (Δρ/ρ0)im. On the other hand, in crystalline alloy series with strong, resonant electron scattering, such as Ni-Fe, Fe-Cr, Fe-V, (Δρ/ρ0)ph is found to be negative and has a minimum at the composition where (Δρ/ρ0)im is maximum.