Optical evidence of mixed-phase behavior in manganite films

Synchrotron infrared measurements were conducted on a self-doped La(x)MnO(3-delta) (x similar to 0.8) film. From these measurements we determined the conductivity and the temperature dependence of the effective number of carriers. While the metal-insulator transition temperature (T(MI)) and the magnetic ordering temperature (T(C)) approximately coincide, the onset of the change in the free carrier density occurs at a significantly lower temperature (similar to 45 K below). This suggests that local distortions exist below T(MI) and T(C) which trap the e(g) conduction electrons. These regions with local distortions constitute an insulating phase which persists for temperatures significantly below T(MI) and T(C).