We report electrical transport experiments on the colossal magnetoresistance compound $({\mathrm{L}\mathrm{a},\mathrm{C}\mathrm{a})\mathrm{M}\mathrm{n}\mathrm{O}}_3$ over a wide range of composition and temperature. Comparison of thermopower and electrical resistivity measurements above the metal-insulator transition indicate a transport mechanism not dominated by spin disorder, but by small polaron formation. Additionally, we find that in the high-temperature limit the thermopower corresponds to backflow of spin entropy, expected from motion of positively charged particles in a rigid $S=2\mathrm{}$ system, showing a remarkable independence of $S=3/2\mathrm{}$ particle density.

• Received 18 November 1996

DOI:https://doi.org/10.1103/PhysRevB.56.5104