Symbiotic strategy of Cu on CuFe₂O₄ realizing high-efficiency electromagnetic wave absorption

Low complex permittivity and easy magnetic agglomeration prevent ferrites from achieving high-efficiency electromagnetic wave (EMW) absorption owing to the resultant narrow absorption bandwidth. Existing composition- and morphology-controlled strategies have made limited progress in fundamentally improving the intrinsic complex permittivity and absorption performance of pure ferrite. In this study, Cu/CuFe₂O₄ composites were synthesized using a facile and low-energy sol-gel self-propagating combustion, and the metallic Cu content was adjusted by changing the ratio of the reductant (citric acid) to the oxidant (ferric nitrate). The symbiosis and coexistence of metallic Cu with ferritic CuFe₂O₄ increases the intrinsic complex permittivity of CuFe₂O₄, which can be regulated by changing the metallic Cu content_. Moreover, the unique ant-nest-like microstructure overcomes the issue of magnetic agglomeration. Because of the favorable impedance matching and strong dielectric loss (interfacial polarization and conduction loss) provided by the moderate metallic Cu content, S0.5 concurrently displays broadband absorption with an effective absorption bandwidth (EAB) of 6.32 GHz at an ultrathin thickness of 1.7 mm and strong absorption relying on minimum reflection loss (RL_min) of -48.81 dB at 4.08 GHz and 4.0 mm. This study provides a new perspective for improving the EMW absorption performance of ferrites.