Faraday Activity in Flexible Maghemite/Polymer Matrix Composites

Homogeneous 10-30 nm γ-Fe₂O₃ (maghemite) nanoparticles have been synthesized on magnesium silicate fibers and further incorporated into a polymeric matrix (polystyrene). The similarity in the refractive indices of both materials (n_Sep = 1.53 and n_PS = 1.59) and the optimal dispersion allowed obtaining highly transparent composites from near IR to the visible range. Therefore, particles of γ-Fe₂O₃ appear perfectly dispersed inside a heterogeneous but transparent matrix, and consequently, it is possible to measure their Faraday rotation. These composites present a ferromagnetic behavior, yet close to superparmagnetism due to the size of the γ-Fe₂O₃ particles. High real in-line transmittance in the visible range together with a Faraday activity over 0.4° are obtained in 60 μm films, which is over twice larger than that reported for commercially available devices based on single crystal terbium gallium garnets.