Improved microwave absorption properties of CoFe2O4/AC nanocomposites from matching electromagnetic characteristics

•CoFe2O4 nanoparticles are introduced into AC to form CoFe2O4/AC nanocomposites.•The good RLmin and EAB should be attributed to electromagnetic loss and impedance matching.•AC enhances microwaves propagation path, leading to multiple reflections and scattering.•The conductivity AC increases conduction loss and eddy current loss.•The impedance matching is optimized by the introduction of AC. In order to eliminate the impact of microwaves on safety and health, the development of microwave absorption materials with strong, thin, light and broad characteristic is particularly important. In this paper, magnetic CoFe2O4 nanoparticles are introduced into the pores of coconut activated carbon (AC) to form CoFe2O4/AC nanocomposites. The specific surface area and saturation magnetization both decease with the increasing AC content, confirming the existence of CoFe2O4 nanoparticles in AC pores. The microwave absorption performance of CoFe2O4/AC nanocomposites are all greatly enhanced due to impedance matching. Specifically, S-8 (The molar ratio of AC:CoFe2O4 = 8:1) demonstrates a remarkable minimum reflection loss (RLmin) of −42.99 dB and an effective absorption bandwidth (EAB) of 0.96 GHz at a thickness of 5.5 mm. Moreover, S-12 exhibits an RLmin of −24.00 dB and a broader EAB of 3.44 GHz at 1.5 mm. The exceptional microwave absorption performance of the CoFe2O4/AC nanocomposites can be attributed to a synergy of dielectric loss, magnetic loss, and impedance matching mechanisms. These mechanisms encompass interface polarization, dipole polarization, Debye relaxation, natural loss, conduction loss, eddy current loss, as well as multiple reflection and scattering effects.