Magnetic and Magnetoresistive Properties ofNanocrystalline Pr_(1-x)A_xMn_(1-y)Co)yO_3 (A= Sr, Ca;x = 0.3, y = 0.5)

摘要

Nanocrystalline Pr_(1-x)A_xMn_(1-y)Co)yO_3 (A = Sr, Ca; x = 0.3, y = 0.5) samples are prepared by sol-gel method. The XRD pattern show single phase and cubic crystal structure with a (=b=c) = 3.862 nm at room temperature. The crystallite size of the samples are calculated using Scherrer formula and found to be ～15 nm and ～24 nm for Pr_(0.7)Sr_(0.3)Mn_(0.5)Co_(0.5)O_3 and Pr_(0.7)Ca_(0.3)Mn_(0.5)Co_(0.5)O_3 respectively. The SEM images show the particles are spherical in shape and average particles sizes are about ～20 nm and ～25 nm. The samples undergo paramagnetic to ferromagnetic transition about ～ 172 K and ～153 K. The temperature dependence of resistivity (p) data show insulating behaviour below 80 K and from 80 K to 300 K, the samples behave like semiconductor. Variable range hopping conduction is found to be dominating for temperatures above 80 K. The maximum magnetoresistance is found to be ～ 35 % and ～ 24 % at 100 K and it has negative sign.