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Yttrium iron garnet (YIG) film made as a magneto-optical medium suffers from the problem of crack formation, caused by the heating process. YIG thin film is deposited by radio frequency RF magnetron sputtering; the obtained layer is amorphous and it needs annealing to be crystallized. After heat-treatment at 740 o C of the sample realized on quartz substrate, we observe cracks on the entire film surface. This is due to the large difference between the thermal expansion coefficient (5.5 x 10 -7 K -1 for quartz and 10 x 10 -6 K -1 for YIG). In this paper we present a new fabrication method to reduce this problem, we make a multilayer to obtain at the end a uniformly unique layer with excellent crystalline structure. Such films have the possibility to reach a thickness of 500 nm. YIG films have been studied by Rutherford Backscattering Spectrometry (RBS), opticEllipsometry and the Scan Electron Microscope. The RBS spectra were collected in channelling geometry with incident particles energy 2 MeV and 3.5 MeV. The thickness and the stoichiometric value of the thin films have been evaluated. Simulation of all spectra indicates a constant composition. Ellipsometry method is well adapted to model the thin film structure layers, and to measure the thickness of the film and the complex index of refraction. The theoretical ellipsometric value of the index of refraction is (2.22) while the experimental value is ranging from 2.2 to 2.3 for a wavelength of 1550nm.

Composite thin films made of cobalt ferrite nanoparticles embedded in silica/zirconia sol-gel matrix are presented, and their versatility is illustrated through the impact of the nanoparticle features on the films’ final properties. The intrinsic magneto-optical potentiality of the nanoparticles is especially given by a peak around 1550 nm in the spectra of both the Faraday rotation and the magneto-optical figure of merit. These nanoparticles are inserted in the liquid preparation of a sol-gel host matrix, which is coated on a glass substrate at soft temperature. SEM and optical analysis show the absence of nanoparticle aggregates and defects into thin films and prove the ability of these films to be used as a guiding layer for photonic integration. The dispersion in the host matrix and the integration on a substrate do not affect the merit factor of the material. The specific Faraday rotation of the films is about 300°/cm for a volume fraction of nanoparticles of 1.5%, and it possesses a hysteresis loop. Its dependence on the nanoparticle mean size offers the possibility to achieve self-biased behavior. In addition, a magnetic field applied during the coating promotes an alignment of the magnetic easy axis of the nanoparticles along a preferential direction. It allows increasing even more the remanent magneto-optical effect and also reducing the birefringence and reaching a TE/TM phase matching of the film guided modes. It gives a way to tune these two parameters that play a crucial role in magneto-optical devices.

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PACS 78.20.Ls, 85.70.Sq Thin films of Yttrium Iron Garnet (YIG) are grown by radio frequency magnetron non reactive sputtering system on quartz and Gadolinium Gallium Garnet (GGG) for optical applications or alumina substrates for microwave applications. A post deposition annealing is needed to obtain the crystallization of YIG films and the magnetic properties which are correlated with the magneto-optical properties. Their crystallographic, morphologic and magnetic properties are explored. The variation of Faraday rotation is studied versus the wavelength. For both optical substrates, quartz and GGG, results are comparable with the literature for bulk material. A microwave isolator was realized with YIG thin film on alumina substrate in a coplanar configuration.

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