Magnetotransport and thermoelectric power of La2/3Ba1/3Mn1−xSbxO3 (x=0–0.05) manganite perovskites

The effect of Sb+5-doping on the magnetotransport and thermoelectric power of La2/3Ba1/3Mn1−xSbxO3 (x  =0–0.05) perovskite manganites is reported here. Two insulator–metal (I–M) transitions have been observed in the electrical resistivity–temperature ρ(T)ρ(T) behavior of the undoped sample La2/3Ba1/3MnO3. Both the transitions (at TP1TP1 and TP2TP2) shift to lower temperatures with doping but to a different extent. TP1TP1 decreases faster while TP2TP2 remains almost invariant up to 3% of doping and then decreases. With increasing Sb+5 content, the intrinsic magnetoresistance (MR at TP1TP1) gets suppressed whereas the extrinsic magnetoresistance at lower temperatures gets enhanced. The thermoelectric behavior S(T)S(T) of the pristine sample shows a peak at TP1TP1 while for the doped samples the peak gets suppressed. All the samples exhibit a crossover in their S(T)S(T) behavior from positive to negative at a temperature T∗T∗, indicating that the dominant carrier in these compounds changes from hole to electron above T∗T∗. Transport behavior above TP1TP1 (the paramagnetic insulating region) is explained on the basis of the small polaron hopping model while the electron–magnon scattering process has been invoked to explain the thermoelectric power and electrical resistivity behavior in the ferromagnetic regime.