Microwave Electromagnetic Properties Of The Nd₂Co₁₇ And Y₂Co₁₇ Micron Flakes Fractured Along C-crystal Plane

The high-frequency soft magnetic material working in GHz region has attracted intense attention due to its wide applications such as miniature inductance, miniature antenna, noise suppressor, and radar-wave absorber. All these applications have the strong requirement of high permeability in GHz region.Conventional spinel ferrite materials are unable to satisfy the requirements of high-frequency applications due to the restriction of Snoek limit. The 2:17 rare earth magnetic alloy material is our research group developed a new type of microwave absorbing materials, the easy magnetization plane of such materials is caused by the magnetic anisotropy, out-plane field is higher than Fe and Fe-based alloy flaky particles several times, we can obtain larger Snoek product. However, our group previous studies have focused on the irregular particles due to the limit of experimental conditions. This powder has the following disadvantages:（1） The outplane field is unable to further enhance because it was only determined by the magnetic anisotropy.（2） Compared to the thickness only a few hundred nanometers of powder, this material has the obvious eddy current effect, it is not conducive to maintaining a high magnetic permeability at higher frequencies. Therefore, we expect to prepare micron flakes with thickness at nanoscale. The out-plane field of such materials would be the sum of magnetic anisotropy field and shape anisotropy field, greatly increased the ratio of out-plane and in-plane field. The material will have higher permeability at high frequency.Based on the above theoretical analysis, we have chosen the easy-plane material Y₂Co₁₇ and Nd₂Co₁₇. To prepare micron flakes fractured along c-crystal plane and investigate microwave electromagnetic properties of the flakes/epoxy composites. The main conclusions are as follows:1. Nd₂Co₁₇ flakes1) We successfully prepared the Nd₂Co₁₇ micron flakes fractured along c-crystal plane. The best prepared conditions are that n-heptane acts as the milling media and the milling time selects 4 h.2) The nature resonance frequency of all Nd₂Co₁₇ flakes/epoxy composites exceeds 10 GHz. It is not obvious that change in the volume fraction effects microwave permeability. As the volume fraction increase, the resonance frequency decrease significantly. Using LLG equation to fit the permeability curve of volume fraction of 35% sample, the resonant frequency of the composite is 15.7 GHz. Compared to inherent Snoek limit 19.6 GHz, this sample has higher Snoek product 23.5 GHz.3) We calculate microwave reflection loss of the epoxy composite with volume fraction of 35%. This sample has excellent electromagnetic wave absorption properties in C-X band, the reflection loss stronger than-10 d B in 4.8-17.0 GHz.4) The tempering could not improve microwave electromagnetic properties of Nd₂Co₁₇ micron flakes.2. Y₂Co₁₇ flakes1) We use the same method to prepare Y₂Co₁₇ micron flakes fractured along cplane.2) The real part of initial permeability of all volume fraction epoxy composites is about 5.1, and this value increases with volume fraction increase. In addition, the resonant frequency locates in 5-7 GHz range.3). Using LLG equation to fit the permeability curve of volume fraction of 40% sample, the intrinsic resonant frequency is 7.5 GHz. Compared to inherent Snoek limit 9.2 GHz, this sample has higher Snoek product 30.7 GHz.4) We calculate microwave reflection loss of the Y₂Co₁₇ epoxy composite with volume fraction of 40%. This sample has excellent electromagnetic wave absorption properties in L-S band, the reflection loss exceeds-10 d B in 1.0-4.7 GHz.