Magnetic and electrical transport properties of La0.67Ca0.33MnO3 (LCMO):: xZnO composites

We have synthesized La0.67Ca0.33MnO3 (LCMO):xZnO (0 less than or equal to x less than or equal to 0.475) composites through a citrate gel route and have characterized them for magnetic and magnetotransport properties. In lower concentrations (x less than or equal to 0.13), ZnO mostly goes into the perovskite lattice substituting Mn in LCMO and segregates less in the grain boundary region, but at higher concentration (x > 0.13) it segregates mostly at the grain boundaries of LCMO and influences the transport properties significantly. A model is proposed which describes the overall resistivity of the system as a parallel combination of a low resistive intragrain conducting path and a high resistive intergrain insulating path. Using this approach, the grain and grain boundary contributions to the overall resistivity are separated for all the composites. The field dependent resistivity shows that all the composites have higher values of MR at the transition temperatures (T-MI) compared to that in pure LCMO (x = 0). The highest value of MR is obtained for x = 0.10 and is 76.6% at 80 kOe field near T-MI.