Thermopower studies of rare earth doped lanthanum barium manganites

Influence of rare earth doping on electrical, magnetic and thermopower studies of La0.34Re0.33Ba0.33MnO3 compound was investigated. Ferro to paramagnetic transition and metal to insulator transition temperatures decrease with decreasing ionic radius of the dopant ion. Electrical resistivity in the entire temperature range is explained by phase separation model. The magnitude of Seebeck coefficient increases with increasing dopant ionic radius. A cross over from negative to positive sign has also been observed in thermopower data with decreasing A site ionic radius (〈rA〉). The low temperature thermopower data has been explained using a qualitative model containing diffusion; magnon drag and phonon drag effects while the paramagnetic insulating part has been analyzed using small polaron hopping mechanism.