Magnetic, electronic, dielectric and optical properties of Pr(Ca:Sr)MnO_3

摘要

The charge-ordered perovskite Pr_(0.65)Ca_(0.28)Sr_(0.07MnO_3 was investigated by means of magnetic susceptibility, specific heat, dielectric and optical spectroscopy and electron-spin resonance techniques. Under moderate magnetic fields, the charge order melts yielding colossal magnetoresistance effects with changes of the resistivity over eleven orders of magnitude. The optical conductivity is studied from audio frequencies far into the visible spectral regime. Below the phonon modes hopping conductivity is detected. Beyond the phonon modes the optical conductivity is explained by polaronic excitations out of a bound state. ESR techniques yield detailed informations on the (H,T) phase diagram and reveal a broadening of the linewidth which can be modeled in terms of activated polaron hopping.