Faraday rotation measurements in maghemite-silica aerogels

Abstract

Faraday rotation measurements have been performed on γ-Fe₂O₃/SiO₂ nanocomposite aerogels which are light, porous and transparent magnetic materials. The materials have been prepared by sol–gel polymerization of a silicon alkoxide, impregnation of the intermediate silica gel with a ferrous salt and supercritical drying of the gels. During supercritical evacuation of the solvent, spherical nanoparticles of iron oxide, with a mean particle diameter of 8.1±2.0 nm, are formed and are found to be homogenously distributed within the silica matrix. The specific Faraday rotation of the composite was measured at 0.6 T using polarized light of 810 nm, being 29.6°/cm. The changes in the plane of polarization of the transmitted light and the magnetization of the material present similar magnetic field dependencies and are characteristic of a superparamagnetic system.