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

ε-FeSUB2/SUBOSUB3/SUB 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 ε-FeSUB2/SUBOSUB3/SUB/SiOSUB2/SUB 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 ε-FeSUB2/SUBOSUB3/SUB phase, which exhibits the largest coercive field among the Fe oxides. The sample treated at 1,075 °C had the highest percentage of ε-FeSUB2/SUBOSUB3/SUB phase, with a coercivity (HC) 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 ε-FeSUB2/SUBOSUB3/SUB within the temperature range of 40-150 K. The crystal structure of ε-FeSUB2/SUBOSUB3/SUB 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 ε-FeSUB2/SUBOSUB3/SUB is a promising candidate with high electromagnetic-wave absorption capacity that is appropriate for high-speed wireless communication applications.