Spin-wave and spin-fluctuation contributions to the magnetoresistance of weakitinerant-electron ferromagnets

Abstract

The spin-wave and exchange-enhanced spin-density fluctuation contributions to the electrical resistivity,ρ(T),of weak itinerant-electron ferromagnets are calculated in the absence and presence of the magneticfield, H, employing the two-band (s- and d-band) model and the version of spin-fluctuation theory ford-band that makes use of the Ginzburg–Landau formalism. These self-consistent calculations(i) mark a substantial improvement over the previous theoretical treatments in that theycompletely dispense with the unrealistic electron-gas approximation, (ii) account for the effect ofH on thecontributions to ρ(T) arising from spin waves (spin-density fluctuations) at low temperatures (atintermediate temperatures and for temperatures close to the Curie point,TC), and (iii) regardless of the nature of the low-lying magnetic excitationsthat dominantly contribute to the negative magnetoresistance,Δρ/ρ, in different temperature ranges, yield analytical expressions that basically have a simplegeneral form . The expressions, so obtained, not only permit a quantitative determination ofthe suppression of spin waves and spin fluctuations by the magnetic field,H, in weakly ferromagnetic metals from the magnetoresistance data but are also capable ofyielding useful information about the band structure.