LATTICE-DYNAMICS IN COLOSSAL MAGNETORESISTANCE MANGANITES

Based on the Hamiltonian of small polarons with strong electron-phonon interaction, we have investigated anomalous behaviors of the sound ve locity in colossal magnetoresistance (CMR) manganese oxides. In the lo w-doping metallic regime, the sound velocity has been found to be hard ened below the ferromagnetic transition temperature T-c due to T-depen dent electron screening coming from the double exchange (DE) interacti on. On the contrary, in the high-doping regime (x > 0.5), the charge o rdering (CO) interaction rather than the DE induces the hardening of t he sound velocity by the ordering of localized polarons around the CO transition temperature T-co. (C) 1998 Elsevier Science B.V. All rights reserved.