Construction of core-shell structured Co₇Fe₃@C nanocapsules with strong wideband microwave absorption at ultra-thin thickness

Constructing magnetic/dielectric composites with core-shell structure is an effective strategy for the development of high-efficiency microwave absorbers owing to the synergistic effect of multiple attenuation mechanisms. In this work, FeCo₂O₄ nanoparticles of 8 nm prepared by the nitrate decomposition method were used as the precursor, and the core-shell structured Co₇Fe₃@C nanocapsules with an average particle size of only 30 nm were fabricated through subsequent carbonization-reduction process. The Co₇Fe₃@C nanocapsules exhibit high-efficient microwave absorption performance. At an ultra-thin thickness of 1.6 mm, the minimum reflection loss (RL) value reaches up to −117.4 dB at 11.9 GHz. Notably, at the same thickness, the effective absorption bandwidth (RL ≤ −10 dB) is as wide as 9.2 GHz (8.8–18 GHz), covering almost the whole X and Ku bands. Moreover, the microwave absorption mechanism is revealed in detail through in-depth analysis of electromagnetic parameters. The outstanding microwave absorption capability is ascribed to the synergetic effect of strong magnetic loss of Co₇Fe₃ alloy cores and strong dielectric loss of amorphous carbon shells, as well as the superior impedance matching. It is believed that the core-shell structured Co₇Fe₃@C nanocapsules should be promising as high-efficiency microwave absorbers with thin thickness, strong absorption strength and broad absorption bandwidth.