Effect of Heat-treatment Temperature on the Formation of -Fe₂O₃ Nanoparticles Encapsulated by SiO₂

epsilon-Fe2O3 has received attention with particular interest because of its large coercive field at room temperature, high-frequency millimeter-wave absorption, and the coupling of its magnetic and dielectric properties. This work investigated the effect of heat treatment on the formation of epsilon-Fe2O3/SiO2 composites fabricated using reverse-micelle and sol-gel methods. The heating process was performed at various temperatures to figure out the optimal conditions for acquisition of the epsilon-Fe2O3 phase, which exhibits the largest coercive field among the Fe oxides. The sample treated at 1,075 degrees C had the highest percentage of epsilon-Fe2O3 phase, with a coercivity (H-C) of 21.57 kOe measured at room temperature that reached a maximum of 23.7 kOe at 230 K. The measurement of the magnetization-temperature (M-T) curve for this sample also reveals the characteristic magnetic transition associated with epsilon-Fe2O3 within the temperature range of 40-150 K. The crystal structure of epsilon-Fe2O3 was confirmed using X-ray powder diffraction. Transmission electron micrographs revealed a broad size distribution of iron oxide nanoparticles ranging from 12 to 22 nm. The findings indicate that epsilon-Fe2O3 is a promising candidate with high electromagnetic-wave absorption capacity that is appropriate for high-speed wireless communication applications.