Microstructural, Electrical-, Magneto-Transport Properties of Grain Size Modulated Nanocrystalline Nd_(0.67)Sr_(0.33)MnO_3 CMR Manganites

摘要

We have investigated the effect of nanometric grain sizes on Microstructural, electrical-, magneto-transport and magnetic behaviors in nanocrystalline Nd_(0.67)Sr_(0.33)MnO_3 CMR manganites. Three nanocrystalline powders of Nd_(0.67)Sr_(0.33)MnO_3 were synthesized through chemical route "Pyrophoric Reaction Process" and calcined for 5 hrs at calcinations temperature (T_(Cal)=650°C, 750°C, and 850°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_(0.67)Sr_(0.33)MnO_3 powders (～30, 40, and 54nm for T_(Cal)=6.50°C, 750°C, and 8.50°C respectively). TEM micrographs show that the average particle sizes are in nanometric regime (Φ～30-50nm). In AC susceptibility and resistivity measurement we observed that there is an almost constant Curie temperature (T_C) has value around 240K and gradual decrease of metal-insulator transition temperature (T_p) (from 200-129K) with decrease of T_(Cal). The magneto resistance of ultra fine nanoparticles increases with grain sizes. Highest magnetoresistance observed ～24 for Nd_(0.67)Sr_(0.33)MnO_3 with T_(Cal)=850°C. Experimental results revels, the effect of nanometric grain sizes has an important impact in magnetic properties and magneto-transport behaviors.