Magnetic-Response-Regulated Impedance Matching and Distributed Microwave Absorption in Co−Fe/Epoxy Composites

Efficient polymer-based microwave absorbers require incident waves to enter the material and then be sufficiently attenuated inside the absorber. This balance is difficult to achieve when design relies only on high dielectric loss. Here, Co−Fe/epoxy (Co−Fe/EP) composites are used as a dual-magnetic model platform in which the Co/Fe ratio regulates magnetic storage, magnetic loss, interfacial polarization, and input impedance while the epoxy matrix maintains a moderate dielectric response. The optimized composites exhibit an effective absorption bandwidth of up to 6.42 GHz and a minimum reflection loss of −54.04 dB at millimeter-scale thicknesses. A numerical magnetic-parameter reconstruction and sensitivity-analysis framework is established using the measured permittivity and reconstructed permeability. The reconstructed response agrees closely with the measured-parameter result, giving an RL root-mean-square error of 0.286 dB. Removing the magnetic response or setting μ″ to zero eliminates the effective absorption region, whereas independent tuning shows that μ″ mainly regulates attenuation intensity and μ′ controls peak migration and the input-impedance trajectory. Area-based analysis further demonstrates that effective broadband absorption is associated with the overlap of impedance-matching and attenuation regions rather than with the maximum of any single loss parameter. Density functional theory calculations support Co−Fe interfacial d-orbital coupling and localized charge redistribution as microscopic origins of interfacial polarization. These results establish a reproducible magnetic-response-regulated framework for balancing wave accessibility and internal attenuation in epoxy-based absorbers.