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