Microwave Absorption Properties Of FeSi,FeNi Magnetic Particles With Easy-Plane Anisotropy

With the wide application of electronic equipment and communication facilities,electromagnetic interference has caused a serious impact on human life,industrial and military applications.Therefore,it is urgent to research and develop materials for microwave absorption and electromagnetic interference resistance.It is well known that an excellent microwave absorbing material should be lightweight,thin thickness and exhibit a high absorbing intensity and wide absorbing band simultaneously.In recent years,magnetic materials(i.e.,Fe,Co,Ni,and its alloys)are widely used in microwave absorption due to their excellent electromagnetic properties,high saturation magnetization and high Snoek limits.Besides,they also have a large refractive index,can compress the wavelength,and have both magnetic loss and dielectric loss.Up to now,the research on magnetic microwave absorption materials mainly focuses on the X(8-12 GHz)band,while the research on the S(2-4 GHz)and L(1-2 GHz)bands are particularly rare.Because high-performance absorbers working in lower frequencies with small thickness need much higher permeability,conventional magnetic materials with axis anisotropy cannot fulfill this requirement.Based on the impedance matching theory and the quarter-wavelength model,for Fe-based magnetic particles,high permeability and the matched dielectric constant are more favorable for obtaining thin thickness efficient absorption in a low-frequency band.Besides,according to the magnetic moment precession double anisotropy model,high permeability can be achieved at GHz level for soft magnetic material with easy-plane anisotropy because its high-frequency characteristic is expressed by:fr(?i-1)=?/4?(?)(1)Where H? is an in-plane anisotropic field and H? is an out-of-plane anisotropicfield.For magnetic materials with easy anisotropy,the anisotropy field outside the plane is much larger than the anisotropy field inside the plane.Therefore,this material can easily break the limit of Snoek limit,so that the sample maintains high permeability at the GHz level,which is more conducive to obtaining thin thickness absorber at lowfrequency band.However,magnetic metal alloys with high permeability tend to have higher permittivity,which significantly weakened the microwave absorption performance.To obtain excellent microwave absorption performance,impedance matching must be satisfied,and the material should have a dielectric constant matching the magnetic permeability.Previous studies have shown that surface modification of magnetic particles is an effective way to reduce the dielectric constant and improve absorption performance.Therefore,to obtain excellent absorbing performance at S and L bands,based on the above theory and model,the Fe-Si and Fe-Ni magnetic particles with easyplane anisotropy are prepared,and their surface modification is carried out to improve their impedance matching performance.Their electromagnetic characteristics,microwave absorption properties and the absorption mechanism are studied.