Research On Preparation And Microwave Absorbing Properties Of CoFe₂O₄ Composites

The popularization of electronic devices and wireless communications has brought an increasingly significant convenience to our daily life,whereas generating electromagnetic interference is becoming a remarkable negative impact on ecological balance and human health.To solve these adverse effects,we are facing an urgent need for high-performance microwave absorbers based on broadband,wide strength,low thickness,and lightweight,which can convert most of the electromagnetic energy into thermal or other forms of energy.Particularly,spine ferrite Co Fe₂O₄ has been widely researched on account of its medium saturation magnetization,high coercivity,as well as strong magnetocrystalline anisotropy.However,the high resistivity of Co Fe₂O₄ leads to poor dielectric properties,which grievously hinders its widespread application.The excellent microwave absorption properties of materials are highly associated with two aspects of the impedance matching and attenuation characteristics,which can actually be achieved through modulating the electromagnetic parameters of the absorbers.To eliminate the disadvantages of single Co Fe₂O₄,this article adopts the preparation of magnetic/dielectric composites to prepare competitive microwave absorbers.By effectively regulating the electromagnetic parameters of the composites by adjusting the composition and designing special morphology,to obtain excellent microwave absorption performance.The idiographic study detail is as follows:1.The spinel ferrite Co Fe₂O₄and multi-walled carbon nanotubes(MWCNTs)composites are constructed by a facile one-step solvothermal method.The pure phase of Co Fe2O4 particles is confirmed by X-ray diffraction patterns.Microstructure analysis demonstrates that monodisperse Co Fe2O4 microspheres are wound by MWCNTs.With the addition of CNTs,there is a striking raise in the imaginary part of permittivity(??)with the composites.The champion microwave absorption performance can be achieved in the composites by the balance of complex permittivity and permeability.When the mass fraction of CNTs is 3%,a minimum reflection loss(RLmin)of the composites is as high as-46.65 d B at 14.4 GHz at a thin thickness of 1.5 mm,and the corresponding effective absorption bandwidth below-10d B reaches 4.91 GHz ranging from 12.41 to 17.32 GHz which covers almost the whole Ku band(12.0-18.0 GHz).It is proved that the introduction of CNTs increases the interfacial polarization and dielectric loss,and the effective complementarities of magnetic loss and dielectric loss can effectively improve microwave absorption performance.2.The Co Fe2O4/Mo S2 composites have been well constructed via a facial hydrothermal method,from which the porous Co Fe2O4 microspheres were embedded into Mo S2 ultrathin nanosheets.As a typical two-dimensional transition metal sulfide,Mo S2 with high electrical conductivity and flexible properties is expected to exhibit high dielectric loss and magnetic loss when combined with magnetic material Co Fe2O4.Meanwhile,the unique hierarchical structure of as-synthesized Mo S2nanoflowers is conducive to scattering and reflection of electromagnetic waves and endows designed composites with competitive microwave absorption properties.As expected,the results demonstrate that as-fabricated Mo S2/Co Fe2O4 composites do have superior microwave absorption properties in comparison with Co Fe2O4 and Mo S2.It is found that the complex permittivity is enhanced with increasing filling ratio from 45 wt%to 60 wt%,which helps obtain a moderate permittivity value.When the filling ratio is 50 wt%,the Mo S2/Co Fe2O4 composites exhibit a minimum reflection loss(RLmin)of-53.1 d B at 12.08 GHz when the thickness is 2.5 mm.An effective absorption bandwidth reaches 6.61 GHz(11.28 to 17.89 GHz)at a thin thickness of 2.2 mm,almost covering the whole Ku-band.The magnetic material integrated with dielectric material can efficaciously modulate the impedance matching degree and the attenuation ability of the absorber,to achieve a better microwave absorption effect.Generally speaking,cobalt-based spinel ferrite composites were prepared by a simple and low-cost method.By modulating the electromagnetic characteristics of the absorber,the impedance matching and attenuation constant were optimized to achieve good absorbing performance.A series of experiments proved that the synergistic effect of the magnetic and dielectric materials always played a significant effect on the improvement of microwave absorption performance.