Electrical and thermal transport measurements on semimetallic rare-earth sesquisulfides

Measured values of $\rho$, $R_H$, $\alpha$, and $\kappa$ are reported on single-crystal samples of ${\mathrm{Nd}}_2$ ${\mathrm{S}}_3$, ${\mathrm{Gd}}_2$ ${\mathrm{S}}_3$, and ${\mathrm{Dy}}_2$ ${\mathrm{S}}_3$ containing excess rare earth in the defect lattice structure. Measurements cover the temperature range between roughly 7 and 1000 K, and an excess rare-earth composition range between 0.1 and 0.7 wt%. Data can be interpreted in terms of the Cutler-Mott model modified for magnetic effects by von Molnár, Holtzberg, Penney, and their associates. Above 100 K, alloy scattering appears dominant. At lower temperatures the transport mechanism favors a hopping process for localized electrons in a magnetically ordered lattice.