Interface engineering in the hierarchical assembly of carbon-confined Fe3O4 nanospheres for enhanced microwave absorption

Heterointerfaces can induce dielectric polarization relaxation to remarkably boost microwave absorption performance. However, delicately engineering a homogeneous magnetic-dielectric heterostructure remains a considerable challenge. Herein, novel hierarchical Fe3O4@C microspheres have been successfully fabricated via polydopamine confinement and sequential calcination. In the product, each primary nanoparticle (Fe3O4 microsphere) is confined within a thin layer of carbon, constructing a multi-interface heterostructure. Interface engineering in such a hierarchical assembly of Fe3O4@C core-shell nanoparticles results in unique performance superiority in terms of microwave absorption compared with traditional carbon-coated Fe3O4 microspheres. The maximum reflection loss value reaches -55.4 dB, and the broad effective absorption bandwidth covers a range as wide as 9.5 GHz (8.5-18 GHz) at only 2.0 mm. Importantly, the confinement effect simultaneously results in strong magnetic coupling interactions and a well-defined charge distribution at the contacted interfaces, which ultimately enhance the magnetic loss and dielectric loss, respectively. Besides, the dielectric carbon shell with optimized thickness facilitates the spread of the magnetic flux line, leading to intensive magnetic-dielectric synergy as well as matched impedance. These results might provide a new insight into the preparation of highly efficient microwave absorbers by optimal microstructure engineering.