Microwave absorption enhancement of e-Fe₃O₄@C microspheres by core surface modification

Magnetic particles can be combined with carbon materials to prepare core-shell microwave absorbers and the proper core/shell weight ratio yields the optimal absorption effects. However, few studies have focused on the influence of core surface modification on the microwave absorption performance. In this work, e-Fe₃O₄@C composite microspheres are synthesized by surface etching of core Fe₃O₄ microspheres in HCl followed by polymerization/carbonization. Core surface modification improves the microwave absorption capability of the e-Fe₃O₄@C microsphere films. The minimal reflection loss (RL_min) is −54.38 dB at 12.4 GHz for a film thickness of 2.6 mm and the maximum effective bandwidth is extended to 4.1 GHz (3 mm). Etching of the Fe₃O₄ core surface increases the interfacial contact area consequently enhancing interface polarization and defects created by surface etching produce additional dipole polarization to further increase the dielectric loss. The underlying mechanism is investigated and described. The results reveal a novel and effective strategy to enhance the properties of core-shell microwave absorption materials.