On-line phase transition in La_1−xSr_xMnO₃ (0.28 ≤ x ≤ 0.36) perovskites through ultrasonic studies

Abstract

La_{1− x} Sr _x MnO₃ perovskite manganite materials with different compositions (x = 0.28, 0.31 and 0.36) have been prepared employing solid-state reaction technique. On-line evaluation of ultrasonic velocities and longitudinal attenuation of the above samples has been done over a wide range of temperatures using the transmission method. The observed anomalies in velocities, attenuation and elastic moduli reveal the occurrence of lattice softening and hardening near Curie temperature. The observed dramatic hardening in sound velocities and softening in attenuation are correlated with the phase transition, i.e. ferromagnetic to paramagnetic. The increase in magnitude of maximum velocity with change in Sr content at T _c indicates the existence of linear magnetostriction effect. The elastic moduli study elucidates the observations made from the above-mentioned studies. The variation in the ultrasonic velocities, longitudinal attenuation and its derived parameters help us to understand the competitions between ferromagnetism and paramagnetism.

Keywords:

• perovskite
• ultrasonics
• Curie temperature
• electron–phonon interactions
• electron–electron interactions

Acknowledgements

The authors are very grateful to the Department of Science and Technology, New Delhi for the financial support to carry out this research project (SP/S2/M-27/2001 dt. 07.07.03).