Strong magnetoelastic effect in Pr1−xCaxMnO3

Manganese oxides with distorted perovskite structure have attracted much attention during the last decade due to their colossal magnetoresistance (CMR), and the strong correlations among the various degrees of freedom involved. In particular, Pr1−xCaxMnO3 compounds present in a wide Ca-doping range a charge ordering phenomenon, consisting of real space ordering of Mn3+ and Mn4+ in alternate lattice sites below a certain temperature TCO. This ordering brings about a lattice distortion and a large hardening of the sound velocity below TCO. Tomioka et al. have observed that an applied magnetic field can melt this charge ordered state and induce a transition from an insulating to a metallic state. In order to study the effects of this charge order melting, ultrasonic longitudinal sound velocity measurements were performed on polycrystalline Pr1−xCaxMnO3 (x=0.35 and 0.5) as a function of magnetic field and temperature. Interesting anomalies were found related to the melting of the charge ordered phase into a metal-like state even at low temperatures.