Stabilization of the high coercivity [formula omitted] phase in the [formula omitted] nanocomposites

Abstract

We have investigated the processes leading to the formation of the Fe2O3 and CeO2 nanoparticles in the SiO2 matrix in order to stabilize the ϵ-Fe2O3 as the major phase. The samples with two different concentrations of the Fe were prepared by sol–gel method, subsequently annealed at different temperatures up to 1100°C, and characterized by the Mössbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe2O3 phases under various conditions of preparation was investigated, starting with the preferential appearance of the γ-Fe2O3 phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major ϵ-Fe2O3 phase for high Fe concentration and high annealing temperature, coexisting with the most stable α-Fe2O3 phase. A continuous increase of the particle size of the CeO2 nanocrystals with increasing annealing temperature was also observed.