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To meet the current requirements for absorbing materials with broadband, lower thickness, and lower density, the FeNi@C@Fe 3 O 4 magnetic powders with a density of 1.75 g/cm3 are constructed by the hydrothermal method and the liquid phase reduction method. The powders have good matching performance with air impedance in the band of 0.3 GHz ~ 18 GHz, and can consider both dielectric loss and magnetic loss-absorbing mechanisms. The loss tangent, tgδ, of the powders is 0.4–0.5. The powder coat is designed by using the interference absorption mechanism. When the thickness of the coat is 1.8 mm, the absorption peak of the coat is about − 30 dB. The coat has a maximum of effective absorption band for 12.2 GHz ~ 17.3 GHz, and the effective absorption bandwidth is 5.1 GHz. When the glass fiber/epoxy resin composite material of thickness 0.5 mm is coated on the FCFp coat of thickness 1.7 mm, the effective absorption band is further widened to 11.9 GHz ~ 17.6 GHz, and the effective absorption bandwidth reaches 5.7 GHz. The FeNi@C@Fe 3 O 4 powders have the characteristics of dielectric and magnetic loss-absorbing materials, and have the remarkable advantages of the wider effective absorption bandwidth and the lower density, which is a kind of high-efficiency absorbing material with outstanding comprehensive absorption performance. [Display omitted] [ABSTRACT FROM AUTHOR]