Studies of transport and magnetic properties of Ce-doped LaMnO3

The X-ray diffraction, electrical resistivity (ρ), piezoresistance, thermoelectric power (TEP, S) and magnetisation experiments have been performed on polycrystalline La1-xCexMnO3 (x=0-0.6) samples over a temperature range (20-320 K). All the compounds except x=0.1 display a metal-insulator (MI) transition at TMI. From the analysis of the resistivity data we find that the double peaks observed in the ρ(T) data of ceramic samples are originating from the grain boundary effects. Moreover, the charge conduction at higher temperature occurs by means of a thermally activated polaron hopping mechanism. The application of pressure suppresses the resistivity and enhances the resistive transition temperature (TMI) and hence the Curie temperature (TC). The thermopower (TEP, S) of all the samples is positive and above TC, both the ρ(T) and S(T) curves show that charge conduction at high temperatures takes place according to Emin and Holstein's theory of adiabatic polaron hopping. At low temperatures, thermal variation of the magnetization (M) can be explained considering the conventional spin wave theory containing T3/2 and T2 terms. In the paramagnetic region, the M(T) data fits well with the Curie-Weiss law