Theoretical consideration of Faraday rotation spectra in bismuth substituted yttrium iron garnet films

It is well known that bismuth substituted rare earth iron garnet (R3-xBixFe5O12, Bi:RIG, where R denotes rare earth element) exhibit large magneto-optical Faraday rotation in wavelengths ranging from the visible to infrared regions. The origin of Faraday rotation of Bi:YIG (i.e. yttrium is used for R in the above chemical formula) films was investigated theoretically by Scott et al. and Shinagawa. Simsa et al. also attempted to interpret their Faraday rotation spectra (FRS) data of LPE grown Bi:YIG films with the bismuth content X < 0.3 theoretically. However, no theoretical studies of FRS for heavy substituted Bi:YIG films have been done. Thus we attempted to explain FRS of Bi:YIG films with the bismuth content x < 2.0 by making a modification of the theories.