Microwave Magnetic Properties Of Rare Earth Intermetallic Powder With Easy-plane Anisotropy

High frequency permeability of magnetic materials is becoming more and more important in nowadays national defense industry. It’s because the performance of magnetic devices operating at high frequency strongly depends on the permeability dispersion behaviors, such as cellular phones, common-mode choke coils and corresponding electromagnetic (EM) wave absorbers. Especially, the EM wave absorption properties in S-band (2-4GHz). For example, Wi-Fi network at2.4GHz, microwave ovens at2.45GHz, and fixed satellite at2.4,2.6GHz. According to current EM wave theories, the permeability (μr) of materials should be improved to obtain a smaller matching thickness (tm) in a lower S-band frequency. Generally, the capability of traditional high frequency magnetic materials with uniaxial anisotropy can be well discribed by Snoek’s theory, the product of the initial permeability and resonance frequency is proportional to the saturation magnetization, which therefore significantly limits the application of materials. However, in recent years, the planar ferrites, especially planar anisotropy soft magnetic thin films and planar anisotropy flake-shaped particles, have shown higher resonance frequency and higher permeability at higher frequencies than that of the bulk materials and most spherical particle composites. The high frequency magnetic properties then can be improved by changing out-of-plane and in-plane magnetocrystalline anisotropies.According to the theory above, the Y2Fei7, Y2Fei7Nx and Y2Fe17-xCox particles have been prepared and the magnetocrystalline anisotropy properties were also studied using different methods. At last, we discussed the high frequency magnetic properties of Y2Fe17, Y2Fe17Nx and Y2Fei7-xCox paraffin compounds. The main results are obtained as follows:Y2Fe17magnetic powders1. The intensity of the [004] diffraction is strongly enhanced when XRD measurement is performed on the oriented composite surface perpendicular to the cylindrical axis proved that the Y2Fe17are planar anisotropy magnetic structures in atmosphere temperature;2. The Snoek value is4.6GHz for the Y2Fe17composite with30vol%, where the Ms is the saturation magnetization of Y2Fei7powders. However, for planar anisotropy Y2Fe17powders, the value of the permeability is related to the out of plane anisotropy-field Ha and in plane anisotropy-field Hp, it is observably found that the product of the initial permeability and the nature resonance is larger than the value calculated by Snoek limit. The result is around12.6GHz, where the natural resonance is7GHz (fitting frequency) and the initial permeability μi, is2.8;3. The paraffin composites admixture30vol%Y2Fe17powders exhibited excellent microwave absorption properties in the frequency range of1-10GHz with the thickness of1-8mm. The minimum reflection loss of unoriented and oriented Y2Fe17composites were-48dB at2.34GHz and-59dB at3.4GHz, and the corresponding thickness was only3.9mm and2.3mm, respectively.Y2Fe17Nx magnetic powders1. The intensity of the [004] diffraction is strongly enhanced when XRD measurement is performed on the oriented composite surface perpendicular to the cylindrical axis proved that the Y2Fe17Nx are planar anisotropy magnetic structures in atmosphere temperature;2. The paraffin composites admixture30vol%Y2Fe17Nx powders exhibited excellent microwave absorption properties in the frequency range of1-10GHz with the thickness of1-8mm. The minimum reflection loss of unoriented and oriented Y2Fe17composites were-34dB at0.91GHz and-39.5dB at0.816GHz, and the corresponding thickness was only8.95mm and8.5mm, respectively.Y2Fei7-xCox magnetic powders1. According to the orientation XRD measurement, we obtained that the when x<6, the compounds presented planar anisotropy, x=8was cone anisotropy and x>10was uniaxial anisotropy;2. We improved the anisotropy measurement method of materials and the results show that for different magnetocrystalline anisotropies, we can just change the orientation direction to obtain the magnetocrystalline anisotropy field;3. The Mossbauer spectroscopy of Y2Fe17-xCox with different x values show that the Fe occupancy ratio is dramatically different from other three and the competition between magnetocrystalline anisotropy of Fe and Co atoms at these four sites results in different type of anisotropy of Y2Fe17-xCox compounds.4. The results of high frequency magnetic properties of Y2Fe17-xCox show that the cone anisotropy Y2Fe9Co8has higher nature resonance frequency and higher initial permeability; 5. According to the theory derivation, we found that the high frequency magnetic properties of cone anisotropy materials was inversely proportional to the sinθ(θ is the cone angle).