Microstructural, Electrical-, Magneto-Transport Properties of Grain Size Modulated Nanocrystalline Nd_0.67Sr_0.33MnO₃ CMR Manganites

Abstract

We have investigated the effect of nanometric grain sizes on Microstructural, electrical-, magneto-transport and magnetic behaviors in nanocrystalline Nd_0.67Sr_0.33MnO₃ CMR manganites. Three nanocrystalline powders of Nd_0.67Sr_0.33MnO₃ were synthesized through chemical route “Pyrophoric Reaction Process” and calcined for 5 hrs at calcinations temperature (T_Cal = 650^o C, 750^o C, and 850^o C). XRD patterns indicate that all the synthesized powders have pseudo-cubic perovskite structure without any secondary impurity phase. Using Debye Scherrer formula we calculated the crystallites size for three nanocrystalline Nd_0.67Sr_0.33MnO₃ powders (~ 30, 40, and 54 nm for T_Cal = 650^o C, 750^o C, and 850^o C respectively). TEM micrographs show that the average particle sizes are in nanometric regime (φ ~ 30-50 nm). In AC susceptibility and resistivity measurement we observed that there is an almost constant Curie temperature (T_C) has value around 240 K and gradual decrease of metal-insulator transition temperature (T_P) (from 200-129 K) with decrease of T_Cal. The magneto resistance of ultra fine nanoparticles increases with grain sizes. Highest magnetoresistance observed ~ 24 for Nd_0.67Sr_0.33MnO₃ with T_Cal = 850^o C. Experimental results revels, the effect of nanometric grain sizes has an important impact in magnetic properties and magneto-transport behaviors.