Magnetotransport properties of ${\mathrm{La}}_{0.6}{\mathrm{Pb}}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ and ${\mathrm{Nd}}_{0.6}{\left({\mathrm{Sr}}_{0.7}{\mathrm{Pb}}_{0.3}\right)}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ single crystals

Magnetotransport measurements of high-quality single crystals of ${\mathrm{La}}_{0.6}{\mathrm{Pb}}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ and ${\mathrm{Nd}}_{0.6}{\left({\mathrm{Sr}}_{0.7}{\mathrm{Pb}}_{0.3}\right)}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ show a close relationship between giant magnetoresistance and the ferromagnetic ordering transition in these materials. In contrast to results for thin film and polycrystalline materials, magnetoresistance of these single crystals vanishes as $T\to 0$. A two-component polaron model provides a possible framework for the interpretation of the previously unexplained variation in the functional form of $\rho \mathrm{}\left(H\right)\mathrm{}$ above and below the Curie temperature.