Temperature-Dependent Scattering in ParamagneticPdCoAlloys

Measurements are presented of the resistivities of some dilute $\mathrm{Pd}\mathrm{Co}$ alloys at temperatures above the magnetic-ordering temperature. The excess resistivity $\Delta \rho$ can be represented by the expression $\Delta \rho =A+B\ln T$, where $B$ is positive and is proportional to the Co concentration. Magnetoresistance measurements on one of the alloys are also presented. It is shown that an implausibly large positive value for the exchange coupling between $s$ electrons and local spins is required to account for the magnetoresistance and zero-field measurements if the temperature dependence is assumed to result from a Kondo scattering of the $s$ electrons from local Co moments. We conclude that the mean-square moment on the impurity site may be temperature dependent, due either to partial spin compensation by the itinerant $d$ electrons or localized spin fluctuations on the Co sites, and that this leads to a temperature-dependent scattering of the $s$ electrons and the resistivity behavior which we observe.