Study on enhanced microwave absorption characteristics of annealed Fe₃O₄

Fe₃O₄ was synthesized by the hydrothermal method in one step. The grain size, morphology, and microwave absorption performances were modified effectively by heat treatment in a vacuum environment at different temperatures. Compared with the Fe₃O₄ before annealing, the minimum reflection loss value of Fe₃O₄ after annealing at 850 °C reaches − 27.5 dB at a thickness of 1.6 mm, with the effective absorption band reaching 5.68 GHz (10.32 GHz to 16 GHz). This result is due to the emergence of the second-phase Fe₂O₃ in Fe₃O₄ after annealing at 850 °C. The interfacial coupling between Fe₃O₄ and Fe₂O₃ leads to additional polarization. Moreover, the considerable absorption bandwidth resulted from better impedance matching and excellent attenuation performance. Therefore, it has broad application prospects as a microwave absorber.