KH550@Fe3O4/rGO composites have improved hydrophobicity for wide use in humid environments, demonstrating their ultra-thin and high-intensity EMW absorption capability owing to their special structure.

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C/CoLaxFe2−xO4 (with x = 0.1, 0.2, 0.3) composites were compounded by using a high‐temperature hydrolysis. X‐ray Diffraction (XRD) and X‐ray Photoelectron Spectroscopy (XPS) results show that doping of La ions does not alter the spinel crystal structure and partially replaces Fe ions. Results of Field‐Emission Scanning Electron Microscope (FESEM) and Energy Dispersive Spectroscopy (EDS) mapping prove that with the doping of La ions, the grains are refined, and the carbon shell on the surface exists. The effect of doping of La ions on microwave absorption performance of the composites was systematically studied. It is found that an optimal reflection loss (RL) of −49.56 dB is achieved at 4.96 GHz, as the composition is C/CoLa0.2Fe1.8O4. Meanwhile, the sample C/CoLa0.3Fe1.7O4 shows excellent effective absorption bandwidth. Specifically, when the matching thicknesses are 4 and 5 mm, the effective absorption bandwidth is 4 GHz, covering the C band and Ku band, thus realizing multiband absorption. The synergistic effects of the enhanced dipole polarization related to the doping of La ions, improved interface polarization of the core‐shell structure, and the magnetic loss originated from CoLaxFe2−xO4 are responsible for the optimal microwave absorption performance. Therefore, this C/CoLaxFe2−xO4 composite material has the prospect of a multiband high‐efficiency microwave absorber.

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