Production of Rare-Earth-Free Iron Nitride Magnets (α″-Fe16N2)

To realize rare-earth-free magnets, we studied iron nitride (α″-Fe16N2) magnets, which contain no rare-earth elements. Fe-N powder with the α″-Fe16N2 phase has a high saturation magnetization comparable to high-performance rare-earth magnets but is not stable at temperatures over 539 K. We consolidated Fe-N powder into bulk material at low temperatures by spark plasma sintering (SPS) and spark plasma sintering with dynamic compression (SPS-DC). Fe-N magnets were successfully obtained at low temperatures of 373–573 K. The magnets produced by the SPS-DC method had a higher density than those produced by the SPS method. The density of the magnets produced by the SPS-DC method increased as the consolidation temperature increased. That produced at 373 K had a saturation magnetization of 1.07 T with a coercivity of 0.20 MA/m.