Low-Temperature Resistivity in a "Giant" Moment Alloy

Resistivity measurements have been made on a dilute alloy of 0.07 at.% Co in Pt in the temperature range of 1.0 to 20°K. We find that the net resistivity, ${\rho }_{\mathrm{alloy}}-{\rho }_{\mathrm{purePt}}$, is linearly proportional to $+\ln T$ in this temperature range, in accordance with Kondo's $s-d$ exchange scattering theory when the effect of ordinary scattering is taken into account. We also find that the net resistivity is linearly proportional to ${〈{\mu }_{\mathrm{eff}}\mathrm{}\left(T\right)\mathrm{}〉}^2$, where ${\mu }_{\mathrm{eff}}\mathrm{}\left(T\right)\mathrm{}$ is the effective moment associated with the Co impurity and surrounding Pt electrons, which decreases at lower temperatures, as deduced from ${\mathrm{Pt}}^{195}$ nuclear-magnetic-resonance linewidth measurements in the same system. This kind of behavior is predicted by Knapp's two-band model.