The Kerr effect in nanosized BiYIG structures on GGG and YAG substrates

The polar Kerr effect in ultrathin Bi-doped yttrium iron garnet (BiY2Fe5O12) films is studied in the energy range 1.3 eV < E < 4.5 eV in constant external magnetic fields of up to 12 kOe at room temperature. The films with thicknesses ranging from 5 to 55 nm are produced by high-vacuum magnetron sputtering on single crystalline gadolinium-gallium Gd3Ga5O12 (111) and yttrium-gallium Y3Al5O12 (211) garnet substrates. All the films exhibit high structural perfection and significant magneto-optical response. Kerr rotation for the films reaches up to +0.33° in a 2 kOe saturation field. It is shown that a decisive role in the spectral and field dependences of the Kerr effect for the thin-film nanostructures on polished substrates is played by the contribution of reflected light and the magneto-optical properties of the substrate. For example, for the substrates with a polished back side, the Kerr effect is negative and reaches about −0.42°, which is comparable in magnitude with the effect in the films. At the same time, there is practically no Kerr rotation for the substrates with a diffuse scattering back side, and the spectral dependence of the effect for the thin-film nanostructures is close to the dependences for bulk samples of the same composition. The findings can be of interest for specialists in magneto-optics and the synthesis of thin-film magnetic nanostructures based on yttrium iron garnet.