In order to recycle the abandoned Nd -Fe -B sintered magnets, we attempted to develop a high coercive magnetic powder for bonded magnets from the Nd -Fe -B sintered magnet scraps. It was found that the coercivity of the powders obtained from the Nd -Fe -B sintered magnet scraps could be fully recovered by the thermally activated surface treatment. The powders were mixed with some surface modifiers like DyF 3 and subsequently annealed. An anisotropic Nd -Fe -B powder obtained from the sintered magnet scrap, exhibited i H c = 13.2 kOe and B r = 11.0 kG. The recovery of such high coercivity was mainly attributed to the microstructural change favourable to reduce the nucleation sites of the reverse domains.

Iron nanoparticles were synthesized by chemical vapor condensation (CVC) without the aid of LN 2 chiller. The powder synthesized at 400 °C was a mixture of amorphous and crystalline α-Fe. Fully crystallized iron particles were then obtained at and above 600 °C. When the reactor temperature was 1000 °C, however, nonmagnetic γ-Fe was stabilized together with α-Fe. The synthesized particles, mostly possessing the core-shell type structure, were all nearly spherical, but the average particle size rapidly increased as the temperature increased. The surface layer that enclosed the iron core and became thicker in smaller particles was Fe 3 O 4 or Fe 3 O 4 -related amorphous. Except for the one synthesized at 1000 °C, the iron nanoparticles were not fully saturated. The iron nanoparticles (~20 nm) synthesized at 600 °C exhibited i H c ~ 1.0 kOe and M s ~ 170 emu/g.