Magnetic properties, crystalline and magnetic microstructures of dual-main-phase (Nd, Ce)-Fe-B sintered magnets

Abstract

The (Nd, Ce)-Fe-B sintered magnets were prepared by a dual-main-phase (DMP) process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and (Nd, Ce)-Fe-B strips. The crystalline and magnetic microstructures of DMP (Nd, Ce)-Fe-B magnets with the remanence of 11.92–12.68 kGs, the intrinsic coercivity of 3.97–5.31 kOe, and the maximum energy product of 23.08–32.99 MGOe have been investigated. Magnetic force microscope (MFM) investigations reveal that the DMP (Nd, Ce)-Fe-B magnets show maze-like patterns, which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large. However, much finer domain structures mixing with coarse ones can be observed obviously in DMP (Nd, Ce)-Fe-B sintered magnets. The size distribution of the domain width of the DMP (Nd, Ce)-Fe-B magnet is not uniform obviously. The average domain width is W = 0.912 μm, and the fine domain width has only 0.216 μm. The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets. This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity. Furthermore, it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM, indicating their ferromagnetism. Obvious correlations between the crystalline microstructure, chemical composition of phases, and magnetic structure were demonstrated for the DMP magnets.