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

Abstract

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.