Integration of magneto-optical active bismuth iron garnet on nongarnet substrates.

For optical communication, high quality magneto-optical active iron garnet films such as Y₃Fe₅O₁₂ are important ceramic systems with extensive applications, e.g., as optical isolators [H. Dötsch et al., J. Opt. Soc. Am. B 22, 240 (2005)], optical modulators, etc. Thereby, garnets stand out due to their high Faraday rotation and low optical losses in the near infrared. Currently, it is desirable to integrate such macroscopic optical components on a single chip (Si, SiO₂, etc.) to build up optical circuits as in the case of microelectronics (integrated optics) or the use for magneto-optical imaging. Up to now, Bi₃Fe₅O₁₂ shows the highest Faraday rotation over 20°/μm. Unfortunately, Bi₃Fe₅O₁₂ forms in a nonthermodynamical way. Thus, it can only be grown on garnet substrates which prevent it from direct deposition on substrates such as Si or SiO₂. In our present work, we studied the integration of Bi₃Fe₅O₁₂ on different SiO₂ substrates using the pulsed laser deposition method. Therefore, we deposited an Y₃Fe₅O₁₂ buffer first which was optimized in a postannealing step above 900 °C in order to form a polycrystalline garnet phase, which is needed for further Bi₃Fe₅O₁₂ growth. We measured the Faraday rotation of the double layered films and intensely studied them with x-ray diffraction, Rutherford backscattering spectroscopy, environmental scanning electron microscopy, and high-resolution transmission electron microscopy. The attained Faraday rotation can be compared with epitaxial Bi₃Fe₅O₁₂ films grown on Gd₃Ga₅O₁₂ substrates or even overcome them due to interference effects in the double layer. So they are highly attractive for magneto-optical imaging. For the determination of the film thicknesses which is usually done by Rutherford backscattering or profilometry, we used another approach. We measured the transmission spectra of the stack which we also derived from a theoretical model that uses a transfer matrix formalism. The thickness of the multilayer can be gained by fitting the spectra. [ABSTRACT FROM AUTHOR]