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| Rare Earth Permanent Magnet Materials: Latest Research Progress in Sintered NdFeB | |
| datetime:2019-09-04 Hits:461 | |
| At present, rare earth permanent magnet neodymium iron boron (Nd-Fe-B) has been widely used in various aspects of life, such as magnetic levitation trains, electric vehicles, wind power, sound and so on. However, the coercivity of sintered NdFeB products is only 20-30% of the theoretical value (Stoner-Walfart limit) (commonly known as Brownian paradox), which severely limits the application of NdFeB. According to the existing theory, the coercive force of sintered NdFeB is mainly determined by the nucleation field required for the reverse magnetic domain generated near the grain boundary during demagnetization. Therefore, it is especially important to carry out three-dimensional quantitative analysis on how the grain boundary affects the coercive force. This not only can deepen the understanding of the coercivity mechanism of rare earth permanent magnets, but also has guiding significance for practical production. [Introduction] Associate Professor Zheng Rongkun (corresponding author) and the first author of the University of Sydney, Dr. Chen Hanjun and the team members used the backscatter diffraction technique, the atomic-scale three-dimensional atom probe technique, and the micromagnetic simulation technique based on the experimental results to simulate the parameters. In the NdFeB, the coercive force is further reduced due to the non-uniform crystals at the nanometer scale, and the three-dimensional quantitative analysis of the grain boundary composition and coercivity is carried out. Studies have shown that the ferromagnetic elements (iron and cobalt) in the grain boundaries of sintered NdFeB are from 67 at 70 nm. % reduced to 10 at. %. The nucleation field required to produce a reverse magnetic domain near the grain boundaries of such a heterogeneous composition is 27% smaller than the nucleation field required to produce a reverse magnetic domain with a uniform grain boundary containing the same ferromagnetic element content. This achievement is not only useful for industrial production, such as controlling the grain boundary composition at the nanometer scale, but also the analytical method used in this paper can be applied to the study of the relationship between the composition and magnetic properties of other magnetic materials. The research results were published in Physical Review Materials under the title "Coercivity degradation caused by inhomogeneous grain boundaries in sintered Nd-Fe-B permanent magnets". |
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