Colossal magnetoresistance study in nanophasic La_0.7Ca_0.3MnO₃manganite

Abstract

In this study we report the effect of sintering temperature on the low field magnetotransport properties of La 0.7 Ca 0.3 MnO 3 manganite synthesized through polymeric precursor route.The La 0.7 Ca 0.3 MnO 3 has been sintered at 600 o C (S6), 700 o C (S7), 800 o C (S8), 900 o C (S9) and 1000 o C (S10).XRD confirms that phase formation starts at 600 o C.All the samples are single phasic having orthorhombic unit cell.The lattice parameters decrease on lowering the sintering temperature (T S ).The crystallite as well as particle size also show strong dependence on the sintering temperature.All the samples possess insulator-metal (T IM ) as well as paramagnetic-ferromagnetic (T C ) transitions.The T C shows a small variation [274K (S10) to 256K (S6)] as a function of sintering temperature whereas the T IM goes down from 267K (S10) to 138K (S6), a strong decrease of 129K.This T C -T IM discrepancy is due to the fact that whereas the former is an intrinsic characteristic, the latter depends strongly on the extrinsic factors e.g.synthesis conditions grain boundaries and associated disorders.For all the samples MR shows strong dependence on T S .The MR increases on lowering the temperature as well as on increasing the field with the occurrence of an intrinsic contribution around T C .These variations of MR for all the samples have been explained in terms of the microstructural variations and spin-polarized tunneling at low temperatures.