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

Abstract

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.

Investigation of magnetite–Co interactions: from environmentally relevant trace Co levels to core–shell Fe3O4@Co(OH)2 nanoparticles with magnetic applications

“…8 Surface-bound Co may improve the magnetic properties of magnetite nanoparticles, by decreasing their magnetic anisotropy at ambient temperature, while keeping a small size, 24–26 which is of great interest for magneto-optic devices, 27,28 electronic devices, 29 data storage, 26,30,31 high-density recording, 32 or even for replacing the rare earths contained in certain permanent magnets. 26,33…”

Large reciprocal magneto-optical effect induced by all-dielectric resonant gratings based on a magnetic nanocomposite

“…As seen in figure 4(a), the RE (pure TRE, red curve) presents a reciprocal hysteresis loop with a coercive field (B c ) that perfectly matches with that of the non-RE loop (TMOKE, blue curve). Indeed, the magnetization of ferrite cobalt NPs presents a hysteresis loop [32]. One can also mention that the TMOKE is linear in magnetization however the TRE is quadratic in magnetization.…”

Small magnetless integrated optical isolator using a magnetized cobalt ferrite film

“…The substitution of Fe 3+ cations in CFO with nonmagnetic metals such as Al 3+ is a promising route to reduce α CFO while improving the MO effect along the way [24,25]. Another approach is the use of CFO-based composite materials such as CFO nanoparticles embedded in a silica/zirconia matrix, achieving α CFO values in the order of ∼dB/cm [35]. However, the relatively low θ F of current CFO composites hinders their application in real devices.…”