ABSTRACT
Among multitudinous magnetic materials, iron-based alloys have received appreciable attention because of their excellent soft magnetic properties, such as high saturation magnetization, high permeability, and good absorbing properties1-3. Extensive studies have been carried out on alloying of Fe-based alloys in recent years. The influencing factors on electromagnetic performance and working mechanisms have been investigated in different emphasis. Kim4 produced nanocrystalline Fe-Co powders and systematically analyzed the influences of grain size on internal strain, MS, and HC. Murakami5 studied the effects of the magnetic domain structure in Co-Ni-Al ferromagnetic-shaped memory alloys and found that it exhibited the B2 to L10 martensitic transformation upon cooling. Koohkan6 focused on the relations between milling time and the morphology, HC,and saturation intrinsic flux density (Js) of the FeNi alloy. In the whole process of milling (0-100 h), the lattice strain, HC,and Js of the Fe-Ni alloy all increased with milling. Wang7 placed emphasis on the aspect ratio, electromagnetic parameter (m = m¢ – jm¢¢, e = e¢ – je¢¢), and reflection loss (RL) of the Fe-Cr-Si-Al alloy and pointed out that the aspect ratio played a key role in the increase of RL. Fe1.5M0.5CoSi (M = V, Cr, Mn, Fe) alloys were synthesized, and their electronic and magnetic properties were studied theoretically using the simulated computation method8. Theoretical calculations
suggested that doping of low-valent atoms helped to change the band structures, leading to 100% spin polarization in Fe1.5Mn0.5CoSi and Fe1.5Cr0.5CoSi and ultimately resulted in magnetic evolution. 3.1 FeSi AlloyCompared to other Fe-based powders, FeSi alloy powders have higher resistivity, which is beneficial to suppress the unfavorable eddy current effect in the GHz frequency region. Figure 3.1 shows the scanning electron microscopy (SEM) micrographs of sieved FeSi powders with a particle size of less than 53, 53-75, 75-106, and 106-150 μm. Most of the particles are spherical, and they could be dispersed uniformly into paraffin due to good sphericity. What’s more, the spherical powders have no shape anisotropy, so when we investigate the influence of particle size on electromagnetic (EM) behavior and microwave absorption properties, the shape anisotropy effect could be neglected.
