Three-dimensional network FeNi/C composites with excellent microwave-absorbing properties.

• The FeNi/C composites were prepared by room temperature precipitation and high temperature calcination. • The synthesized material has a unique three-dimensional network structure that can optimize impedance matching. • The material has the synergistic effect of multi-loss mechanism. • The optimal minimal reflection loss reaches − 52.99 dB at 3 mm. In this paper, the carbon coated iron nickel nanoparticles were obtained by calcining PVP crosslinked iron nickel oxalate. The morphology, structural composition and microwave-absorbing (MA) properties of the composites were analyzed by various characterization methods. The results show that FeNi/C composites have excellent impedance matching characteristics and MA performance in multiple frequency by virtue of their microscopic network structure. At the same time, through the analysis of loss mechanism, we found that the material has high dielectric loss and magnetic loss characteristics. Under the joint action of various loss mechanisms such as interface polarization and eddy current loss, the material has a high reflection loss (RL) value at different frequency. At a thickness of 3 mm, the sample FNC12 has a minimum RL of − 52.99 dB at 3.6 GHz. The effective absorption bandwidth (EAB) (RL ≤ −10 dB) is 1.81 GHz. [ABSTRACT FROM AUTHOR]