BEHAVIOR OF SOUND VELOCITIES IN THE COMPOUNDS LA1-XSRXMNO3 NEAR MAGNETIC AND STRUCTURAL PHASE-TRANSITIONS

The temperature dependences of the transverse V-t and longitudinal V-l sound velocities in single crystals of the perovskites La1-xSrxMnO3 ( x = 0.1, 0.175, 0.2, 0.25) in the temperature interval T = 70 - 350 K are investigated by the resonance method. Anomalies - small minima and kinks in the temperature dependences V-l(T) and V-t(T) - are observed at the Curie points. A strong jumplike increase (by up to 30%) in bot h the longitudinal and transverse sound velocities, which attests to s izable hardening of the acoustic branches of the phonon spectrum, is o bserved near the temperatures of the structural transitions between th e rhombohedral and orthorhombic phases (for x = 0.175, 0.2, 0.25) and at the phase transition to the polaron-ordered state (for x = 0.1). (C ) 1998 American Institute of Physics.