This paper demonstrates a facile and low-cost carbothermal reduction preparation of monodisperse Fe₃O₄/C core-shell nanosheets (NSs) for greatly improved microwave absorption. In this protocol, the redox reaction between sheet-like hematite (α-Fe₂O₃) precursors and acetone under inert atmosphere and elevated temperature generates Fe₃O₄/C core-shell NSs with the morphology inheriting from α-Fe₂O₃. Thus, Fe₃O₄/C core-shell NSs of different sizes ( a) and Fe₃O₄/C core-shell nanopolyhedrons are obtained by using different precursors. Benefited from the high crystallinity of the Fe₃O₄ core and the thin carbon layer, the resultant NSs exhibit high specific saturation magnetization larger than 82.51 emu·g^-1. Simultaneously, the coercivity enhances with the increase of a, suggesting a strong shape anisotropy effect. Furthermore, because of the anisotropy structure and the complementary behavior between Fe₃O₄ and C, the as-obtained Fe₃O₄/C core-shell NSs exhibit strong natural magnetic resonance at a high frequency, enhanced interfacial polarization, and improved impedance matching, ensuring the enhancement of the microwave absorption. The 250 nm NSs-paraffin composites exhibit reflection loss (RL) lower than -20 dB (corresponding to 99% absorption) in a large frequency ( f) range of 2.08-16.40 GHz with a minimum RL of -43.95 dB at f = 3.92 GHz when the thickness is tuned from 7.0 to 1.4 mm, indicating that the Fe₃O₄/C core-shell NSs are a good candidate to manufacture high-performance microwave absorbers. Moreover, the as-developed carbothermal reduction method could be applied for the fabrication of other composites based on ferrites and carbon.

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