Fabrication and magneto-optical responses of Au-Bi:YIG films

We have studied magneto-optical responses of gold-bismuth-substituted yttrium iron garnet (Au-Bi:YIG) composite films in which Au particles are embedded into Bi:YIG in two different ways. First type were samples in which planar arrays of Au particles were introduced into the middle of Bi:YIG films using a step-by-step sputtering technique. Second type were granular films fabricated using simultaneous co-sputtering of Au and Bi:YIG; in these films Au particles occupy positions inside composite films in a random way. Absorption bands associated with localized surface plasmon resonances (LSPRs) were observed in transmission spectra of films of both types. In the spectral range of LSPRs, samples of Au-array type exhibited larger Faraday rotation angles as compared with that for reference Bi:YIG films of the same thickness. However, given that the volume fraction of Au particles was nearly the same for both types, the enhancement of Faraday rotation for samples of Au-granular type was insignificantly altered. Experiments showed that of the primary importance is the role of the interfaces between Au particles and Bi:YIG. Theoretical estimations showed that, in samples of Au-granular type, air shells appeared between Au particles and Bi:YIG during fabrication. In fact, annealing needed for crystallization of Bi:YIG films is always accompanied with an expansion of their thicknesses.