Magnetic properties, phase evolution and microstructure of directly quenched bulk Pr–Fe–B–Nb magnets

The magnetic properties, phase evolution and microstructure of directly quenched bulk Pr9.5Fe90.5−x−yNbxBy magnets have been studied. Proper Nb substitution for Fe at a high B concentration can greatly modify the phase constitution and refine the grain size from the micrometer scale to 50–150 nm. Optimal magnetic properties, i.e. Jr = 0.57 T, iHc = 1296 kA m−1 and (BH)max = 56.8 kJ m−3, were achieved for Pr9.5Fe71.5Nb4B15. The high coercivity results from the large volume fraction of the 2:14:1 phase, fine grains and the appearance of a grain boundary phase in the magnet.