Synthesis and on-line ultrasonic characterisation of bulk and nanocrystalline La_0.68Sr_0.32MnO₃ perovskite manganite

Abstract

La_0.68Sr_0.32MnO₃ perovskite manganite samples were prepared using sonochemical reactor and solid state reaction technique. The ultrasonic velocity, attenuation and elastic moduli of samples were measured using ultrasonic through transmission method, at a fundamental frequency of 5 MHz over a wide range of temperatures. The temperature dependence of the ultrasonic parameters shows an interesting anomaly in all the compositions. The observed dramatic softening and hardening in sound velocities or attenuation is related to phase transitions. The linear magnetostriction effect is more dominant in the perovskite than volume magnetostriction effect which is evident from the observed anomalous in both longitudinal and shear velocities and attenuation. Further, a decrease in grain size in the sintered sample leads to a shift in the ferromagnetic transition temperature (T_C) from 375 to 370 K.