Exchange-spring permanent magnet particles produced by spark-erosion

Exchange-spring permanent magnet particles of composition ${\mathrm{Pr}}_{\text{6.93}}{\mathrm{Fe}}_{\text{85.7}}{\mathrm{B}}_{\text{5.95}}{\mathrm{Nb}}_{\text{1.39}}$ in at. % were prepared by spark-erosion in liquid argon. The best exchange-spring properties were achieved after vacuum annealing the as-sparked powders at 700 °C for ∼5 min, and did not change significantly for anneals up to 120 min. This behavior suggests that the equilibrium dimensions of the “hard” and “soft” phases were determined by the sizes of the spark-eroded particles in which they developed. The ${\mathrm{Pr}}_2{\mathrm{Fe}}_{14}\mathrm{B}$ phase developed as spheres, likely single crystals, in an $\mathrm{\alpha -}\mathrm{Fe}+{\mathrm{Fe}}_2\mathrm{B}$ matrix.