Engineering colloidal photonic crystals with magnetic functionalities

An engineering approach towards combined photonic band gap properties and magnetic functionalities, based on independent nanoscale engineering of two different materials at different length scales, is conceptually presented, backed by simulations, and experimentally confirmed. Large (>200 nm) monodisperse nanospheres of transparent silica self-assemble into a photonic crystal with a visible band gap, which is retained upon infiltration of small (<20 nm) nanoparticles of magnetic iron oxide. Enhancing and tuning Faraday rotation in photonic crystals is demonstrated.