Interface transformation for enhanced microwave-absorption properties of core double-shell nanocomposites

Abstract

Microwave absorption properties of core double-shell nanocomposites with FeCo core, carbon inner shell and CoFe2O4 or mixed FeCo-CoFe2O4 outer shell have been investigated in the 2–18 GHz frequency range. The synergetic effect of the composition and interface evolution of the core double-shell nanocomposites favors the electromagnetic properties. Multiple dielectric/magnetic loss peaks are observed in the frequency dependence of the complex permittivity/complex permeability of the core double-shell nanocomposites. Compared with FeCo/C nanocapsules and CoFe2O4 nanoparticles, new dielectric relaxation peaks at 10.5 and 14.4 GHz and loss peaks at 4 and 16.4 GHz are found, which are ascribed to the interface effect in the (x)FeCo/C/CoFe2O4 nanocomposites, where x is the weight fraction of FeCo/C nanocapsules in the (x)FeCo/C/CoFe2O4 nanocomposites. The absorption bandwidth with reflection-loss (RL) values exceeding −10 dB extends up to 7.2 GHz, covering the 10.8–18 GHz frequency range in the case of the (80 wt%)FeCo/C/CoFe2O4 nanocomposite with a minimum RL value of −25.8 dB at 16.7 GHz. Thanks to the modified composition/crystal size of the outer shell, enhanced microwave-absorption properties are obtained in the (60 wt%)FeCo/C/(FeCo, CoFe2O4) nanocomposite, where the minimum RL value is −38.1 dB at 13.4 GHz and which has a broad absorption bandwidth of 6.7 GHz (RL values exceeding −10 dB), covering the 11.3–18 GHz frequency range by choosing an appropriate absorber thickness.