Magneto-optical and optical properties of Fe-rich Au-Fe alloy films near the fcc-bcc structural transformation region

A set of Au_1-xFeₓ alloy films with $0<x<1$ have been prepared by rf sputtering onto glass substrates kept at 293 K. The x-ray diffraction study reveals fcc structures for the Au_1-xFeₓ alloy films with $x<0.8,$ and bcc structures for $x>0.80.$ The equatorial-Kerr-effect (EKE) spectra for the Au_1-xFeₓ alloy films with bcc and fcc types of structure show noticeably different spectral shapes and magnitudes from each other. Moreover, the EKE value in the UV region for the Fe-rich Au_1-xFeₓ alloy films exceeds that for the pure Fe film. The observed blueshift and redshift of the low- and high-energy peaks, respectively, of the Fe-rich Au_1-xFeₓ alloy films with respect to pure Fe are caused by differences in the optical constants between alloy and Fe films, which cannot explain, on the other hand, the enhancement of EKE value for the bcc Au_1-xFeₓ alloys. The optical-conductivity (OC) spectra for the Au_1-xFeₓ alloy films with bcc type of structure are characterized by an intense interband absorption peak at 2.0 eV, which is completely absent in the OC spectra of the Au_1-xFeₓ alloy films with fcc type of structure. The spectra of absorptive part of the off-diagonal components of dielectric function for the investigated Au_1-xFeₓ alloy and Fe films exhibit a double-peak structure; a peak near 1.8 eV (which does not depend on the composition or the structural state of alloy) and a high-energy peak. The latter is located at 3.3 eV for the Au_1-xFeₓ alloy films with fcc type of structure and at 4.0--4.2 eV for the alloys with bcc structure as well as for the Fe film.