Magnetic Microstructure of Sintered Nd-Fe-B Magnets Made from Casting Strips

The magnetic microstructures of two Dy-Al substituted sintered Nd-Fe-B magnets with the different nominal compositions of Nd_12.2Dy_0.6Fe_80.4Al_0.7B₆(at.%) (composition-A, C-A) and Nd_13.7Dy_0.6Fe_78.8Al_0.7B_6.2(at.%) (composition-B, C-B) prepared by strip casting technique have been revealed by using a magnetic force microscope. The magnetic properties of sintered C-B magnets are worse than that of C-A sintered magnets. In particular, the value of density products (BH)_max for sintered C-A magnets is about 32% higher than that of C-B magnets, which is reflected by their quite different magnetic microstructures. We believe that for the C-B samples, the inappropriate composition and thus the redundant Nd₂Fe₁₇(B) phase of the casting strips make its final magnetic microstructures worse than the C-A, and then deteriorates the performance of the C-B magnets.