Optimized Synthesis of the Elusive ε-Fe₂O₃ Phase via Sol−Gel Chemistry

ε-Fe2O3 nanoparticles embedded in a SiO2 matrix have been synthesized by sol−gel chemistry and high temperature heat treatments. Virtually pure ε-Fe2O3 (in excess of 93%) is obtained, although a two-phase mixture, ε-Fe2O3 + α-Fe2O3, is observed for Fe2O3/SiO2 ratios greater than 37 wt %. The ε-Fe2O3 nanoparticles are stable up to ∼1600 K. Optimized ε-Fe2O3 nanoparticles are ferrimagnetic, with a Curie temperature TC ≈ 510 K, and remarkably high values of room-temperature coercivity, HC = 20 kOe.