Colossal Magnetoresistance Study in Nanophasic La₀.7Ca₀.3MnO₃ Manganite

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In this study we report the effect of sintering temperature on the low field magnetotransport properties of La₀.7Ca₀.3Mnₒ3 manganite synthesized through polymeric precursor route. The La₀.7Ca₀.3MnO₃ has been sintered at 600ᵒC (S6), 700ᵒC (S7), 800ᵒC (S8), 900ᵒC (S9) and 1000ᵒC (S10). XRD confirms that phase formation starts at 600ᵒC. All the samples are single phasic having orthorhombic unit cell. The lattice parameters decrease on lowering the sintering temperature (Tₛ). The crystallite as well as particle size also show strong dependence on the sintering temperature. All the samples possess insulator-metal (TᵢM) as well as paramagnetic-ferromagnetic (TC) transitions. The TC shows a small variation [274K (S10) to 256K (S6)] as a function of sintering temperature whereas the TᵢM goes down from 267K (S10) to 138K (S6), a strong decrease of 129K. This TC-TᵢM 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 Tₛ. The MR increases on lowering the temperature as well as on increasing the field with the occurrence of an intrinsic contribution around TC. These variations of MR for all the samples have been explained in terms of the microstructural variations and spin-polarized tunneling at low temperatures.