Achieving efficiency microwave absorption through optimized impedance matching and attenuation in hierarchical Co@NC@Nano Fe composites

In response to the need for the improvement of electromagnetic wave absorption performance of Co@NC composites, different Co@NC@Nano Fe composite particles with varying Fe content were synthesized with ZIF-67 as precursor through a combination of liquid-phase deposition, high-temperature pyrolysis, and chemical liquid-phase reduction. The microstructure, static magnetic properties, and electromagnetic wave absorption performance of these composites were investigated. The results showed that the synthesized Co@NC particles exhibited a nearly dodecahedral structure with clear boundaries and an average particle size of approximately 1 μm. In contrast, the dodecahedral structure of the Co@NC@Nano Fe particles became less distinct, with a rougher surface that was predominantly covered by spherical Nano Fe particles, resulting in an average particle size of approximately 1.1 μm. The composite samples retained the crystallographic features of Co@NC, although some oxidation of the Fe particles occurred. The hysteresis loops of various Co@NC@Nano Fe composites exhibited a standard “S” shape, with the saturation magnetization initially decreasing and then increasing as the Nano Fe content decreased. The coercivity showed a trend of initial decrease followed by an increase and then a decrease with reducing Nano Fe content, while the remanence remained relatively stable. The real and imaginary parts of the complex dielectric constant of different Co@NC@Nano Fe composites initially decreased and then increased with decreasing Nano Fe content, while the real and imaginary parts of the complex permeability displayed certain fluctuations. The dielectric loss of Co@NC@Nano Fe composites decreased initially and then increased with reducing Nano Fe content, while magnetic losses exhibited significant fluctuations. Both polarization losses and conductive losses were present in the Co@NC@Nano Fe composites, with the attenuation coefficients showing a trend of initially decreasing and then increasing as the Nano Fe content decreased. Through optimization of Nano Fe content, the optimal Co@NC@Nano Fe sample achieved a minimum reflection loss of −41.90 dB at thickness of 1.6 mm and a maximum effective absorption bandwidth of 4.88 GHz at thickness of 1.7 mm.