Defect-induced synergistic engineering of hierarchical heterostructures for microwave absorption

Defect engineering modulates polarization loss by controlling common defects, including oxygen vacancies, impurity atom doping, and lattice defects, thereby improving the electromagnetic wave (EMW) absorption capability. Here, we designed a cobalt–nickel/hollow-Fe 3 O 4 (H-Fe 3 O 4 @CoNi) dual magnetic layer structure coated with nitrogen-doped carbon via a combined hydrothermal and pyrolysis. The dual magnetic architecture not only promotes magnetic loss but also introduces numerous heterogeneous interfaces. Simultaneously, nitrogen doping facilitates defect-induced dipole polarization, synergistically enhancing dielectric loss and impedance matching. By tuning the pyrolysis temperature, the electromagnetic parameters and EMW absorption performance of the composites were effectively optimized. The H-Fe 3 O 4 @CoNi@C-N-800 exhibited the best performance, with an effective absorption bandwidth (EAB) of 5.1 GHz and a minimum reflection loss (RL min ) of −55.6 dB. Density functional theory (DFT) calculations confirmed that electronic redistribution and charge transfer occurred at the N-doped carbon/Fe 3 O 4 –CoNi interface, validating that the enhanced dielectric loss stems from both dipole and interfacial polarization. Furthermore, CST simulation shows that the maximum radar cross section (RCS) value of H-Fe 3 O 4 @CoNi@C-N-800 can be reduced by 15.64 dB m 2 . These results suggest that this composite is a promising high-performance EMW absorbing material.