Optical and magneto-optical properties of highly distorted Fe„100... thin films

TiN-capped epitaxial bcc Fe films exhibit strong changes in the out-of-plane interplanar distance depending on the growth conditions. At room temperature, the increase of the volume per Fe atom appears to be as large as 5%. The observed distortions deviate substantially from elastic behavior. We explain this effect as due to the presence of nitrogen incorporated into the Fe film during the capping layer deposition. In order to elucidate the effect that these distortions might have on the optical and magneto-optical properties, we study the diagonal and off-diagonal elements of the conductivity tensor for both distorted and undistorted structures. This is done by means of spectral ellipsometry and the Kerr effect in polar and transverse configurations in the energy range from 1.5 to 4.5 eV. Theoretical calculations using ab initio techniques for the observed structures are performed and compared with experimental data. Different possible mechanisms for the experimentally observed effects such as distortion, grain size, and orbital hybridization are studied and discussed.