Self-biased magneto-optical films based on CoFe2O4–silica nanocomposite

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.