Measurements of elastic constants in thin films of colossal magnetoresistance material

Measurements of elastic constants of strained 200 and 400 nm thin films, as well as unstrained samples, of the colossal magnetoresistance (CMR) material La0.67Ca0.33MnO3 are presented. Since the peak resistance temperature of a strained CMR film decreases as the film thickness decreases, it is of interest to see if features in the elastic constants, reflecting structural or magnetic changes, follow the peak resistance temperature. It is observed that features in the elastic constants appear not only at the peak resistance temperatures of the CMR samples, but also at a temperature about 17 K higher. A new technique, thin-film resonant ultrasound spectroscopy, was used to make the measurements.