Ultrasonic anomalies in La0.67Ca0.33Mn1-xZnxO3 perovskites

Abstract

Both the longitudinal and transverse ultrasonic sound velocities and attenuations in the single-phase polycrystalline compound La0.67Ca0.33Mn1-xZnxO3 (x = 0.00, 0.05, 0.10, 0.15) have been carefully measured by a conventional pulsed echo technique at a frequency of 10 MHz, between 20 and 300 K. A dramatic increase in sound velocity, accompanied by a sharp peak in attenuation, is observed near the ferromagnetic transition temperature TC for both longitudinal and transverse modes in all samples. This feature implies extremely strong spin-phonon coupling in this system and gives direct evidence for the spontaneous linear magnetostriction effect. At temperatures below 60 K, a dramatic softening in sound velocity accompanied by a sharp increase in ultrasonic attenuation for both longitudinal and transverse modes is observed. The analysis of the results suggests that the softening of the sound velocity for both longitudinal and transverse modes may correspond to the formation of a spin-glass state.