Improvements in the Coercivity of Iron-Based Nanocrystalline Low-Rare-Earth Fe3B-Nd Permanent Magnets

Fe3B-based Nd-Fe-B permanent magnet materials containing Co and M as additives (M=Al, Si, Cu, Ga, Ag, Au) were prepared in an extremely low rare-earth concentration range centered on 4 at%. The hard magnetic properties develop as a result of heat treatment of rapidly solidified amorphous ribbons, which produces a metastable nanocrystalline structure consisting of Fe3B and Nd2Fe14B. Use of the additives considerably reduces the crystallite sizes, and consequently the alloys exhibit higher coercivity than that seen in alloys without additives. Compaction-molded resin-bonded magnets produced from such Nd-Fe-B-Co-M materials have the following magnetic properties: Hcj=300 kA/m to 470 kA/m; Br=0.7 T to 0.9 T; (BH)max=50 kJ/m³ to 73 kJ/m³. Typical values for the temperature coefficients of Br and Hcj of bonded magnets are ¿0.05%/K and ¿0.35 %/K, respectively, in the range from 297K to 413K.