Simple Fabrication of ϵ‐Fe2O3 Nanoparticles Containing Silica Monoliths with Enhanced Coercivity

Abstract

AbstractMost of large‐size permanent room‐temperature hard magnets contain rare‐earth elements. Here, we present the preparation of a large‐size rare‐earth free hard magnet based on the loading of the ordered mesoporosity of a preformed ordered mesoporous silica monolith obtained by a sol‐gel route with the Fe(NO3)3 salt, followed by a simple calcination in air. The investigation of the influence of the thermal treatment temperature as well as the Fe/Si ratio on the microstructure of the ϵ‐Fe2O3/SiO2 nanocomposites reveals well‐controlled ϵ‐Fe2O3 particles size and size distribution. Their magnetic study allows us i) to specify the size of the particles with an enhanced coercivity and ii) to show a linear correlation between the magnetic coercivity of the materials and the mass percent of these particles in the nanocomposites. A ϵ‐Fe2O3 based bulk hard magnet with the highest coercive field of 18 kOe at room temperature was obtained by this synthesis process.