Faraday rotation in magnetic γ-Fe2O3/SiO2 nanocomposites

Faraday rotation spectrum has been measured at room temperature in a magnetic nanocomposite of $\mathrm{\gamma -}{\mathrm{Fe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}{\mathrm{/SiO}}_{\mathrm{2}}.$ The material consists of isolated $\mathrm{\gamma -}{\mathrm{Fe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ nanoparticles dispersed in a silica matrix, and it was prepared through a sol-gel method. The composite contains 18% of $\mathrm{\gamma -}{\mathrm{Fe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ in weight with an average particle size of 20 nm. It has a coercitivity of 30 Oe and an $M_S$ of 6 emu/g. The specific Faraday rotation spectrum exhibits a narrow peak centered around 765 nm, reaching a value of 110°/cm and an absorption coefficient of $\text{64\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}.$ Faraday rotation versus applied field has also been measured, and a cycle similar to the one described by the magnetization has been found.