Study On Microwave Absorbing Properties Of Fe₃O₄ Nanocomposites

Microwave absorbing materials are widely used in the fields of stealth,electromagnetic compatibility and microwave devices.With the development of modern communication technology,the bandwidth and efficiency of microwave absorption becomes more and more important.Fe304 magnetic material has high dielectric loss,but its ferromagnetic resonance frequency is less than 2GHz and then the magnetic loss is low in the range of 2-18 GHz,which restricted its application in radar band.The Fe3O4 nanostructure can change the natural resonance frequency and improve the absorption,so it is of great significance to study the electromagnetic response of Fe304 nanocomposites.In this paper,the preparation of Fe2O3 nanomaterials with different morphology were obtained by hydrothermal method.The Fe304 nanomaterials were prepared by carbon reduction method.The dielectric constant,permeability and microwave absorbing properties of Fe304 nanostructures(including nanoparticles,nanotubes and nanorings)were investigated.The key factors of hydrothermal synthesis of Fe2O3 nanomaterials are reaction temperature,holding time and the concentration of etching agent.Adjusting the concentration of the etching agent can control the nanostructure.Within 12 hours,holding time has great influence on the nanostructure.When the concentration of etching agent is 9.14 ×10-4mol/L,with the increase of holding time,the nanorods changed into nanotubes.When the concentration of etching agent is 2.74×10-4mol/L,with the increase of reaction time,hollow nanospheres changed into nanorings.When the holding time is longer than 12 hours,the complete reaction has no influence on the nanostructure.The dielectric properties show that the dielectric constant of the three is almost the same in the range of 2-18GHz,but difference of the dielectric loss is relatively large.The dielectric loss of Fe304 nanotubes is the highest due to the formation of the conductive network of one dimensional nanotubes.According to the dispersion law of dielectric loss,we firstly confirmed that the dielectric response mechanism of Fe304 is mainly determined by electron relaxation polarization.These three nanostructures all have the ferromagnetic resonance peaks in the range of 2-18GHz.In compared with bulk Fe3O4,the ferromagnetic resonance peaks of as-prepared Fe304 nanostructures shows blue shift,which may be attributed to the increase of the shape anisotropy.The ferromagnetic natural resonance peak blue shift characteristic,which has high magnetic loss in radar the band,can significantly improve the absorbing performance.Due to the matching of the electromagnetic parameters,the double resonance absorption peak is obtained in the range of 2-18GHz.Based on the situation of the double resonance absorption peak,broadband absorption can be realized by using the structure design.The result shows obvious advantage in the design of broadband structure.