NdFeB based magnets prepared from nanocrystalline powders with various compositions and particle sizes by spark plasma sintering

Isotropic NdFeB permanent magnets were prepared by spark plasma sintering. Melt spun NdFeB ribbons with two compositions and four particle size ranges, i.e. 200–400, 100–200, 45–100 and <45 μm, were employed as the starting materials. For the magnets with Nd rich compositions, high density (7·5 g cm⁻³) and good magnetic properties with remanent magnetic polarisation J_r>0·8 T and maximum energy product (BH)_max>100 kJ m⁻³ were obtained. The influence of particle size on the magnetic properties is not very significant. For single phase NdFeB alloys with stoichiometric 2∶14∶1 composition, because of the deficiency of Nd rich phases, it is relatively difficult to consolidate microsized powders into high density bulk magnet, but generally, a larger particle size is beneficial to achieve better magnetic properties, including higher J_r and (BH)_max.