Infrared reflectivity investigation of the phase transition sequence in Pr0.5Ca0.5MnO3

• Study of the effects of orbital, charge and spin orders on the lattice dynamics.
• Phonon optical conductivity spectral moments are used to monitor phase transitions.
• Precursor effects of the AFM order are detected by infrared spectroscopy.

This work reports an infrared reflectivity study of the phase transition sequence observed in Pr0.5Ca0.5MnO3. The need to measure over an extended spectral range in order to properly take into account the effects of the high frequency polaronic absorption is circumvented by adopting a simple approximate method, based on the asymmetry present in the Kramers Kronig inversion of the phonon spectrum. The temperature dependence of the phonon optical conductivity is then investigated by monitoring the behavior of three relevant spectral moments of the optical conductivity. This combined methodology allows us to disclose subtle effects of the orbital, charge and magnetic orders on the lattice dynamics of the compound. The characteristic transition temperatures inferred from the spectroscopic measurements are compared and correlated with those obtained from the temperature dependence of the induced magnetization and electrical resistivity.