Enhanced microwave absorption of Fe3O4 nanocrystals after heterogeneously growing with ZnO nanoshell

To enhance the microwave absorption of Fe3O4 nanocrystals, ZnO nanoshells with a thickness of 2 nm were grown on Fe3O4 nanocrystals by heterogeneous nucleation. After being coated with ZnO nanoshells, the material possesses a far more improved ability for microwave absorption. A minimum reflection loss of −3.31 dB for Fe3O4 nanocrystals alone was improved to a minimum reflection loss of −22.69 dB and with an effective absorption band (RL < −10 dB) covering a frequency range of 10.08–15.97 GHz. The reasons for the enhanced microwave absorption were studied by the use of X-ray absorption near-edge structures at O K-edge, electron spin resonance analysis and microwave electromagnetic parameters mapping. The results indicate that the decoration of the dielectric ZnO shell had varied the dielectric property as well as the oxidization environment and distribution of Fe ions on the surface of the Fe3O4. This well balances the permeability and the permittivity of the nanomaterials and decreases the difficulty of impedance matching the microwave absorber within the free space. This leads to the Fe3O4@ZnO nanohybrids possessing vastly improved microwave absorption as compared to Fe3O4 nanocrystals alone.