DISORDER EFFECTS IN TRANSPORT-PROPERTIES OF WEAK ITINERANT-ELECTRON FERROMAGNETS

The electric and thermal conductivity of weak itinerant-electron ferromagnets in the presence of spin fluctuations and disorder is calculated and the validity of the Wiedemann-Franz law in these systems is discussed. We used the Keldysh-diagram technique to obtain the expression for the conductivities of the clean system as well as the correction due to disorder. The electric conductivity shows a maximum at a low temperature, which characterizes the crossover behavior from the disorder-dominated region to the spin-fluctuation region. The thermal conductivity (kappa/T) also has a maximum at the crossover temperature. The contribution due to spin fluctuations and the quantum correction due to disorder violate the Wiedemann-Franz law while the Drude term restores it as disorder increases. The experimental results for conductivities in disordered weak itinerant ferromagnets in a very low-temperature range are not available. However, we find that our results agree well with the resistivity of amorphous Ni75P16B6Al3, which considered to be a nearly ferromagnetic metal.