Improving magnetic properties in mischmetal-based sintered composite magnets by regulating element distribution

Mischmetal-based magnets were prepared by mixing 60 wt.% (MM,Nd)14.2-xFe79.8+xB6 (x=0, 0.5, 1, and 1.5) with 40 wt.% Nd15Fe79B6 powders. The coercivity is 9.50 kOe in sintered MM9.8Nd4.4Fe79.8B6/Nd15Fe79B6 magnets, and it decreases to 6.61 kOe in MM9.3Nd3.9Fe80.8B6/Nd15Fe79B6 due to the decrease MM-Nd content of (MM,Nd)-Fe-B alloy and the reduction of the amount of intergranular phase. While for further decreasing MM-Nd content of (MM,Nd)-Fe-B, the effect of Nd diffusing into (MM,Nd)-Fe-B phase to substituting for La-Ce is enhanced in the sintered composite magnets, which would lead to a more increase of magnetocrystalline anisotropy in (MM,Nd)-Fe-B phase. So the coercivity increases to 7.70 kOe in MM8.8Nd3.4Fe81.8B6/Nd15Fe79B6, and the energy product of 33.67 MGOe were obtained in this composite magnets with the 40 wt.% mischmetal in total amount of rare earth. Though the average of magnetocrytalline anisotropy decreases in the sintered composite magnets, the increase of anisotropy in local regions possibly gives rise to the enhancement of coercivity. These investigation shows that the magnetic properties could be optimized by regulating the element distribution in the sintered composite magnets.