Research and development of high-performance new microwave absorbers based on rare earth transition metal compounds: A review

The rapid development of information technology urgently requires magnetic materials with excellent magnetoelectric performance under high frequency (GHz band) conditions. A series of investigations of rare earth-iron intermetallic compounds with planar or cone anisotropy lead to the finding that these compounds have attractive features of high saturation magnetization and high resonance frequency f(r). With further research and development, rare earth-iron intermetallic compounds are expected to become a new kind of high frequency soft magnetic material. In contrast to the permanent magnets such as Nd2Fe14B with high uniaxial magnetocrystalline anisotropy field, rare earth-transition metal intermetallics such as R(Fe,X)(12), (R,R')(2) (Fe,X)(14) B, (R,R')(2)(Fe,X)(17), and their nitrides (R,R' are rare-earth, X is the substitutional elements) can be modified to exhibit planar or cone magnetocrystalline anisotropy, achieving excellent soft magnetic properties of higher f(r) as well as higher permeability mu(i) and thus much higher Snoek limit f(r)(mu(i) - 1). These intermetallics powders/paraffin/resin composites show a maximum reflection loss (RL) between -20 and -70 dB in a wide range of 1-40 GHz, and a large effective absorption bandwidth of 2-10 GHz with a small thickness. Notably, the microwave absorbing performance of the intermetallics samples greatly exceeds the traditional absorbing materials due to their high saturation magnetization and high ratio of the out-of-plane magnetocrystalline anisotropy field to the basal plane anisotropy field. Therefore, rare earth-transition metal intermetallics present an advantage for use as a high-performance thin-layer microwave absorber. They also have great potential to be developed into soft magnetic materials and devices with high performance and high stability at high frequency. It thus opens up broad prospects for technology applications.