Resistivity and magnetoresistance of ferromagnetic metals with localized spins

Resistivity, due to spin-dependent scattering of carriers in ferromagnetic metals with localized spins, is studied to investigate the extraordinary behaviors of the resistivity, such as the giant magnetoresistance and the anomalous temperature dependence near the ferromagnetic transition temperature T_c. The resistivity is calculated on the basis of the s-d model by use of the Boltzmann theory. We aim to clarify the effects of the coexistence of spin-independent scattering of carriers, the smallness of the carrier number, the instability of the ferromagnetic state, and external magnetic fields on the resistivity. It is shown that the temperature dependence of the resistivity can exhibit a peak at T_c even in the presence of spin-independent scatterings. This resistivity peak becomes sharp for an almost unstable ferromagnet with a small carrier number. This peak is easily suppressed by magnetic fields, to result in giant magnetoresistance. The effect of the appearance of a half-metallic state on the resistivity is also discussed.