ε-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 ε-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 ε-Fe₂O₃ phase, which exhibits the largest coercive field among the
Fe oxides. The sample treated at 1,075 °C had the highest percentage of ε-Fe₂O₃ 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-Fe2O3 within the temperature range of 40-150 K. The crystal structure of ε-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 ε-Fe₂O₃ is a promising candidate
with high electromagnetic-wave absorption capacity that is appropriate for high-speed wireless communication
applications.