Sintering temperature effect on electrical transport and magnetoresistance of nanophasic La0.7Sr0.3MnO3

Nanophasic La0.7Sr0.3MnO3 (LSMO) samples were prepared by the sol gel method. The samples were sintered at different temperatures ranging from 600 to 1000 degrees C. It is shown that the transport and magnetoresistive properties of LSMO samples strongly depend on the sintering temperature (T-s). A substantial decrease in the insulator - metal transition temperature (T-IM) and an enhancement in resistivity are found on lowering the sintering temperature. Furthermore, a reduction in magnetization and a slight decrease in paramagnetic-ferromagnetic (PM - FM) transition temperatures (T-c) have been observed as the sintering temperature decreases. The magnetoresistance (MR) at T < T-c increases on decreasing the sintering temperature as well as increasing the applied magnetic field. The enhancement in MR on decreasing the sintering temperature is explained by enhanced spin-polarized tunnelling by assuming an increase of the grain boundary contribution as the sintering temperature decreases.