Comparative Microwave Absorption of Dual-Layer Coatings Containing CoFe₂O₄, NiFe₂O₄, and Hexagonal Mn₀.₁₇₆Fe₁.₈₂₄O₃ Nanoparticles

Electromagnetic interference (EMI) shielding effectiveness (SE) and radar-absorbing materials (RAMs) are increasingly vital in aerospace, defense, and telecommunications. In this study, cobalt ferrite (CoFe₂O₄-CFO), nickel ferrite (NiFe₂O₄-NFO), and manganese-based iron oxide (Mn₀.₁₇₆Fe₁.₈₂₄O₃-MFO) nanoparticles were synthesized via a hydrothermal method and incorporated, along with the dual-layer paint formulations, to investigate their EMI shielding performance. The coatings were applied to lightweight fiberglass substrates pre-treated with a primer layer and tested across the 3.2–5.0 GHz frequency range. X-ray diffraction (XRD) analysis confirmed the formation of spinel structures for CFO and NFO, whereas the Mn-based sample crystallized into a rhombohedral Mn–Fe–O-phase. Scanning electron microscopy (SEM) revealed distinct morphological features, including differences in agglomeration among the samples. Vibrating sample magnetometry (VSM) revealed that MFO exhibited the highest coercivity (HC) and squareness ratio, indicating a stronger magnetic anisotropy. The shielding effectiveness was primarily dominated by absorption effects. Among the samples, MFO at 10 wt. % exhibited the highest total SE (~6–7 dB), whereas CFO at 5 wt.% showed reasonable performance (~3–5 dB) with minimal material usage. The results demonstrate that material selection and filler concentration are critical for optimizing EMI shielding effectiveness. These findings contribute to the development of scalable, lightweight, and cost-effective ferrite-based coatings for targeted frequency applications.