Liu Xiangyi, Zhou Bang, Yuan Bin, Liu Zhongwu
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China.
Materials (Basel). 2023 Jul 26;16(15):5260. doi: 10.3390/ma16155260.
The magnetic properties of magnetic nanocomposites consisting of hard and soft magnetic phases are dependent not only on the intrinsic properties but also on the grain structure and volume ratio of the two phases. In this study, we performed a systematic micromagnetic simulation on the magnetic properties of CeFeB/α-Fe and NdFeB/α-Fe nanocomposites. The volume fractions of the hard magnetic NdFeB or CeFeB phase were varied from 80% to 40%, and the grain sizes of the hard magnetic phase and the soft magnetic α-Fe phase were changed independently from 10 nm to 40 nm. The results show that when the grain size of both hard and soft phases is 10 nm and the volume fraction of the hard phase is 70%, the highest maximum magnetic energy product can be obtained in both CeFeB/α-Fe and NdFeB/α-Fe nanocomposites. The hard magnetic properties of CeFeB/α-Fe nanocomposite decrease significantly when the volume fraction of the α-Fe phase exceeds 30%. However, for the NdFeB/α-Fe system, this situation only occurs when the α-Fe volume fraction exceeds 40%. The reason for this is not only because of the low anisotropic field and the smaller exchange coupling length between the soft and hard magnetic phases, but also because of the lower saturation magnetization of the hard phase. The grain size has greater effects on the magnetic properties compared to the volume fraction of the hard magnetic phase. The main reason is that as the grain size increases, the remanence of the nanocomposite decreases sharply, which also leads to a rapid decrease in the maximum magnetic energy product. The simulation results on the effects of phase ratio and grain size have been verified by experiments on melt-spun CeFeB/α-Fe alloys with various compositions prepared by melt-spinning followed by annealing for various lengths of time. Due to the influence of demagnetization energy, the hard magnetic phase with high saturation magnetization is preferred for the preparation of high-performance nanocomposite magnets.
由硬磁相和软磁相组成的磁性纳米复合材料的磁性能不仅取决于其本征特性，还取决于两相的晶粒结构和体积比。在本研究中，我们对CeFeB/α-Fe和NdFeB/α-Fe纳米复合材料的磁性能进行了系统的微磁模拟。硬磁NdFeB或CeFeB相的体积分数从80%变化到40%，硬磁相和软磁α-Fe相的晶粒尺寸分别从10nm独立变化到40nm。结果表明，当硬磁相和软磁相的晶粒尺寸均为10nm且硬磁相的体积分数为70%时，CeFeB/α-Fe和NdFeB/α-Fe纳米复合材料均可获得最高的最大磁能积。当α-Fe相的体积分数超过30%时，CeFeB/α-Fe纳米复合材料的硬磁性能显著下降。然而，对于NdFeB/α-Fe体系，只有当α-Fe体积分数超过40%时才会出现这种情况。其原因不仅在于软磁相和硬磁相之间的低各向异性场和较小的交换耦合长度，还在于硬磁相较低的饱和磁化强度。与硬磁相的体积分数相比，晶粒尺寸对磁性能的影响更大。主要原因是随着晶粒尺寸的增加，纳米复合材料的剩磁急剧下降，这也导致最大磁能积迅速降低。通过对采用熔体快淬法制备的不同成分的CeFeB/α-Fe合金进行不同时间的退火实验，验证了相比例和晶粒尺寸影响的模拟结果。由于退磁能的影响，制备高性能纳米复合磁体时，具有高饱和磁化强度的硬磁相更受青睐。
