Temperature-Dependent Spin-Disorder Resistivity in a Van Vleck Paramagnet

We have measured the resistivity of single-crystal paramagnetic ${\mathrm{Tb}}_x{\mathrm{Y}}_{1-x}\mathrm{Sb}$ with $x=0,0.05,0.20,0.40\mathrm{}$. At low temperatures a resistance anomaly develops in proportion to $x$. The observed resistance anomaly reflects the temperature-dependent probability that the conduction electrons are scattered from the crystal-field-split $4f$ levels of the Tb ions by elastic as well as inelastic processes. A calculation of this anomaly yields excellent agreement for those values of $x$ for which indirect exchange can be neglected.