Magnetotransport, thermoelectric power, thermal conductivity and specific heat of _{Pr2/3 Sr1/3 MnO3} manganite

Magnetotransport and thermal studies of _{Pr2/3 Sr1/3 MnO3} polycrystalline sintered bulk sample are reported here. The resistivity ρ (T) and thermoelectric power S (T) data show an insulator to metal (I-M) phase transition at _TP ≈294 K and _TS ≈290 K, respectively. Magnetization measurement confirms that the sample undergoes a transition from paramagnetic to ferromagnetic phase at a defined Curie temperature _TC =280 K. A substantial increase in magnetoresistance from 2.5% at 280 K to 5% at 77 K has been noticed in a low magnetic field 0.15 T. Small polaron hopping model is found to be operative above the transition temperature _TP, whereas electron-electron and electron-magnon scattering processes govern the low temperature metallic behavior. A detailed analysis of thermoelectric power in the ferromagnetic regime suggests that the complicated temperature dependence of S may be understood on the basis of electron-magnon scattering. A transition from decreasing high temperature thermal conductivity (due to local anharmonic distortions associated with small polarons), to an increasing thermal conductivity (due to decreasing of phonon-phonon scattering) and thereafter a peak at ∼100 K (signifying a crossover from Umklapp to defect-limited scattering) have also been noticed. Specific heat measurements depict a pronounced anomaly near the _TC, indicating the magnetic ordering and magnetic inhomogeneity in the sample.