Persistent photoconductivity in a ferromagnetic-metallic state of a Cr-doped manganite thin film

Photoinduced persistent conductance has been observed in a Cr-doped ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ thin film. The film shows a diffuse phase transition and phase separation that arise from the quenched random fields produced by the Cr ions. Photoexcitation of the sample with a continuous-wave–yttrium-aluminum-garnet laser causes a gradual increase of the conductance in the ferromagnetic-metallic (FM) state, whereas the magnetization and absorption spectra show little change. The persistent conduction is ascribed to the increase in the conducting paths by the optical excitation in the percolative conduction through FM regions, without significant overall growth of the FM regions. The heating effect and the permanent damage to the sample are absent. The temperature dependence of the absorption spectra and the phonon modes were studied and have presented consistent results with the diffuse transition from a charge-orbital ordered insulating to FM phase.