Anomalies in sound velocity and thermal expansion related to charge order and ferromagnetic transitions in Pr0.65Ca0.35(Mn1-z Co z )O3

The charge order (CO), ferromagnetic (FM) and metal-insulator (M-I) transitions have been studied for Pr0.65Ca0.35(Mn1-Z Co Z )O3 (Z=0-0.10) by measuring the sound velocity v s(T), magnetization M(T), electrical resistivity ρ(T) and thermal expansion L(T)/L R. The v s(T) hardening has been found to precisely monitor the CO transition, while the L(T)/L R shrink has been found to be sensitive to the onset of the FM-metallic phase. The competition of CO, FM-metallic and FM-insulating phases has been studied from the viewpoint of the enhanced electron-phonon interaction through the Jahn-Teller effect