Ferromagnetic Co20Ni80 nanoparticles encapsulated inside reduced graphene oxide layers with superior microwave absorption performance

Abstract

An excellent microwave absorber featuring lightweight, broadband, low filling content, strong absorption intensity and tunable electromagnetic properties is urgently needed for innovative electromagnetic interference shielding. Herein, a series of Co₂₀Ni₈₀ nanoparticles with different sizes encapsulated inside reduced graphene oxide layers (rGO/Co₂₀Ni₈₀) were synthesized via a facile hydrothermal method followed by a continuous freeze-drying process. The size of the Co₂₀Ni₈₀ nanoparticles played a crucial role in the microwave absorption properties of the rGO/Co₂₀Ni₈₀ nanocomposites in terms of both the maximum reflection loss value and the absorption bandwidth. In particular, for rGO/Co₂₀Ni₈₀ with Co₂₀Ni₈₀ nanoparticles of 700 nm diameter, a maximum reflection loss value of −54.4 dB at 7.36 GHz was achieved with a low loading content of only 16%. Moreover, compared with previously reported absorption bandwidth values, a wider absorption bandwidth was observed for the rGO/Co₂₀Ni₈₀ nanocomposites, which exceeded 6.02 GHz and covered the entire Ku band. The superior microwave absorption performance can be attributed to the better impedance matching and synergistic effects between the ferromagnetic Co₂₀Ni₈₀ nanoparticles and the dielectric rGO layers, as confirmed by electron holography. This work may provide a new perspective for the development of lightweight, broadband, low-loading-content and high-performance microwave absorbers.