Core/Shell Iron/Oxide Nanoparticles for Improving the Magneto‐Dielectric Properties of Polymer Composites

A simple method to obtain high magnetic permeability (μ_r), high dielectric permittivity (ϵ_r), and low loss polymer composites with core/shell iron/metal oxide particles is developed. Magnetic iron (Fe⁰) particles with protective SiO₂ shells are synthesized in aqueous environment at room temperature. The shells provide electrical insulting layers which decrease energy loss and also prevent the possibility of μ_r decrease due to Fe⁰ oxidation. Furthermore, Fe⁰ particles could also be coated with TiO₂ shells which allow ϵ_r to be tuned. The ϵ_r and μ_r of the resulting polydimethylsiloxane composites are optimized for core‐shell particle doping. The value of ϵ_r is up to 9.8 and most importantly, the μ is close to 2 at 1 GHz with 43 wt% doping of core‐shell particles. The dielectric loss of the composites is less than 0.02.