Magnetic, electronic, dielectric and optical properties of Pr(Ca : Sr)MnO3

The charge-ordered perovskite Pr0.65Ca0.28S0.07MnO3 was investigated by mea ns of magnetic susceptibility, specific heat, dielectric and optical spectr oscopy and electron-spin resonance techniques. Under moderate magnetic fiel ds, the charge order melts yielding colossal magnetoresistance effects with changes of the resistivity over eleven orders of magnitude. The optical co nductivity 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 excitation s 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 mo deled in terms of activated polaron hopping.