Synthesis of carbon-coated cobalt ferrite core–shell structure composite: A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

Cobalt ferrite has problems such as poor impedance matching and high density, which results in unsatisfactory electromagnetic wave (EMW) absorption performance. In this study, the CoFe2O4@C core–shell structure composite was synthesized by a two-step hydrothermal method. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and vector network analysis et al. were used to test the structure and EMW absorption properties of CoFe2O4@C composite. The results show that the reflection loss (RL) of the CoFe2O4@C composite reaches the maximum value of −25.66 dB at 13.92 GHz, and the effective absorbing band (EAB) is 4.59 GHz (11.20–15.79 GHz) when the carbon mass content is 6.01%. The RL and EAB of CoFe2O4@C composite are increased by 219.55% and 4.59 GHz respectively, and the density is decreased by 20.78% compared with the cobalt ferrite. Such enhanced EMW absorption properties of CoFe2O4@C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite, moreover, the carbon coating layer adjusts the impedance matching of the composite, and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.