Heterostructure design of 3D hydrangea-like Fe3O4/Fe7S8@C core-shell composite as a high-efficiency microwave absorber

Abstract In an era dominated by electronic equipment, the development of high-efficiency electromagnetic wave (EMW) absorbers is of great significance in solving electromagnetic (EM) pollution. Micro/Nanostructural engineering for optimizing EMW absorption performance depends on the design of vacancy, defect, and heterogeneous interface, which remains a considerable challenge in adjusting the micro and macro-interface effects. In this work, S atoms are incorporated into a dielectric-magnetic complementary system (Fe3O4/Fe7S8@C) to arouse the polarization effect of vacancies, defects, and non-uniform interfaces, thus tremendously boosting the EM energy attenuation capacity. Besides, the carbon shell provides more propagation paths for the dissipation of EMWs, and dielectric-magnetic synergy improves impedance matching. Eventually, in comparison with Fe2O3 and Fe3O4@C composites, interface-engineered Fe3O4/ Fe7S8@C acquires a much better EM wave absorption performance. Its minimum reflection loss value reaches as much as -56.2 dB with a thickness of only 1.6 mm, and the corresponding effective absorption bandwidth (EAB) is up to 4.5 GHz. This unique hydrangea-like layered structure provides space to facilitate non-uniform coupling between the layers and has strong anisotropy to enhance the magnetic response. The high density of magnetic flux in the nanosheets builds a three-dimensional magnetic coupling network, which is supported by Off-axis electron holography. Besides, the radar cross section from HFSS simulation further confirms that S-doping can favor the best synergy between dielectric and magnetic losses, facilitating the composite to achieve a more optimal impedance matching and improve the absorption capacity. In conclusion, this work presents new ideas for the design of excellent absorbing materials.