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 p(T) behavior of the undoped sample La2/3Ba1/3MnO3. Both the transitions (at T-p1 and T-P2) shift to lower temperatures with doping but to a different extent. T-p1 decreases faster while T-p2 remains almost invariant up to 3% of doping and then decreases. With increasing Sb+5 content, the intrinsic magnetoresistance(MR at T-p1) gets suppressed whereas the extrinsic magnetoresistance at lower temperatures gets enhanced. The thermoelectric behavior S(T) of the pristine sample shows a peak at T-p1 while for the doped samples the peak gets suppressed. All the samples exhibit a crossover in their S(T) behavior from positive to negative at a temperature T*, indicating that the dominant carrier in these compounds changes from hole to electron above T*. Transport behavior above T-p1, (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. (C) 2007 Elsevier Ltd. All rights reserved.