Template-free fabrication of yolk–shell Fe@SiO₂@C composites by thermal reduction: Boosted microwave absorption performance

The yolk–shell structure offers the advantages of low density, high specific surface area, and tunable properties, making it an ideal microstructure for microwave absorption materials. In this study, dopamine hydrochloride served as both a carbon source and a reducing agent, converting Fe₃O₄ into Fe while promoting core–shell separation via volume contraction and gas release during reduction, thereby fabricating yolk–shell Fe@SiO₂@C. The carbon layer improves dielectric properties, the Fe core provides magnetic loss, and the SiO₂ coating enhances the magneto crystalline anisotropy and coercivity of the material. The sample exhibits excellent microwave absorption performance: a minimum reflection loss of −24.84 dB at 18 GHz with a thickness of 1.9 mm, and a maximum effective absorption bandwidth of 6.26 GHz at a thickness of 2.3 mm. This work proposes a novel preparation method for the yolk-shell structure, providing a new solution for improving the effective bandwidth of wave-absorbing materials in the future.