IR absorption and linear dichroism in BiFe0.5Co0.5O3 films

Abstract

The optical density spectra D(hω) of BiFe0.5Co0.5O3 films with thickness d = 230 and 1400 nm on LaAlO3 substrate were studied in the infrared range from 0.09 to 1.65 eV in unpolarized and linear polarized light at room temperature and at T = 80 K in the magnetic field of 4.5 kOe and without the field. The absorption bands at hω ~0.2 and ~0.7 eV are revealed in the D(hω) spectra recorded in unpolarized light and attributed to combination of two-phonon and two-magnon absorption and to d–d transitions in Fe or Co ions, respectively. In the D(hω) spectra of BiFe0.5Co0.5O3 film with d = 230 nm recorded in linear polarized light, the additional bands in the range of 0.3 eV–1.0 eV are found and explained by the nonuniform charge state due to the existence of weakly conductive electric domains and domain walls with higher conductivity and by the scattering of the light on the domains. The position of the bands in the optical density spectra in polarized light D⊥(hω) and D∣∣(hω) depends on the direction of the magnetic field relative to the film and on the temperature, which is explained by the change of the electric domain sizes. The revealed dependence of the optical properties on the magnetic field direction allows recommending BiFe0.5Co0.5O3 films as new functional magneto-optical material.