Optical and magneto-optical properties of ferromagnetic La1-xBaxMnO3 single crystals

The optical and magneto-optical properties of ferromagnetic La1-xBaxMnO3 single crystals with x = 0.15, 0.20 and 0.25 are studied. The components of the permittivity tensor are obtained by spectral ellipsometry techniques and transverse Kerr effect measurements. The Kerr effect spectra depend substantially on the Ba content. The plasma frequency is estimated. In the paramagnetic semiconductor state, the small polarons contribute to conductivity in La0.85Ba0.15MnO3, in La0.75Ba0.25MnO3 no evidence for polarons is found even in the semiconductor state. For La0.85Ba0.15MnO3 (TC = 214 K), the metallic phase is estimated to occupy less than 1% of the total volume at T = 190 K. It is shown that in La0.75Ba0.25MnO3, the energy gap vanishes and the metal-semiconductor transition occurs somewhat below TC rather than at T = TC.