Hierarchical engineering of magnetic-dielectric composite microspheres has attracted increasing attention owing to its potential to enhance electromagnetic wave absorption (EMA) through magnetic-dielectric synergy. However, optimizing magnetic-dielectric balance in composite microspheres at the nanoscale remains a formidable task due to their limited component optimization and microstructural regulation. Herein, a novel approach is proposed to modify conventional carbonyl iron powder (CIP) microspheres via synergistic etching-assembly strategy. By applying a polydopamine coating, successive tannic acid (TA) etching-assembly, and pyrolysis, hierarchical iron@carbon-1/N-doped carbon (Fe@C-1/NC) composite microspheres are obtained. This overcomes the drawbacks of CIP microspheres, including their high density and poor impedance matching, which hinder EMA performance. Hierarchical carbon layer engineering can introduce abundant dipole centers, heterogeneous interfaces, and conductive networks to induce dielectric loss, while magnetic components contribute to magnetic resonance and eddy current loss, as demonstrated by the results. Accordingly, Fe@C-1/NC composite microspheres demonstrate a minimum reflection loss (RLmin) of -70.7 dB and an effective absorption bandwidth of 3.75 GHz at a matching thickness of 2.3 mm. Generally, this work paves the way towards CIP engineering to provide guidance to the future exploration of hierarchical magnetic-dielectric EMA materials.
