The evolution of the optical spectra of LaMnO3 under light n-and p-type doping and the separation of phases

Abstract

The optical absorption spectra of LaMnO3 single crystals, pure and slightly doped with Ce and Sr (7%), were studied in the middle IR region. Ellipsometry measurements were performed in the visible region to determine real and imaginary permittivity parts. The energies of the onset of indirect transitions in LaMnO3 at 293 and 80 K were found to be 0.30 and 0.40 eV, respectively. Impurity absorption bands corresponding to transition in hole and electron clusters were observed. The anomalous temperature dependence of IR absorption was explained by the existence of conducting droplets in the insulated doped crystal matrices at temperatures below the temperature of the appearance of a ferromagnetic contribution. The existence of such a contribution was proved by studying the equatorial Kerr effect. Because of the separation of phases, manganites slightly doped by a nonisovalent admixture can be treated as optically nonuniform media whose properties are similar to those of a composite system with metallic inclusions.