Elastic-moduli and ultrasonic-attenuation anomalies near antiferromagneticphase transitions in La1-xCaxMnO3

Both the longitudinal and transverse ultrasonic sound velocities and attenu ations in the single-phase polycrystalline compound La1-xCaxMnO3 (x=0.63,0. 83) have been measured by a conventional pulse-echo-overlap technique at a frequency of 10 MHz, between 50 and 300 K. The variations with temperature of the Young modulus E, shear modulus G, bulk modulus B, Poisson's ratio si gma, and attenuation alpha have been determined. Anomalies in E, G, B, sigm a, and alpha were observed near the temperature of the charge-ordering tran sition T-CO and antiferromagnetic (AFM) transition T-N. The results imply a very strong spin-phonon interaction caused by linear magnetostriction near the AFM transition. The detailed form of the anomalies is different for di fferent types of phase transitions. (C) 2000 American Institute of Physics. [S0021-8979(00)08205-0].