We report the crystal structure of Nd–Fe alloys as candidates for grain-boundary phases in Nd–Fe–B sintered magnets. We find that the crystal structure of the fluorite Nd–Fe alloys is stable for a wide composition range. We also demonstrate that solid solution of Ga is effective in stabilizing the fluorite crystal structure of Nd–Fe alloys, which is consistent with experimental observations reporting crystalline Nd–Fe alloys at the grain boundaries of Ga-added Nd–Fe–B permanent magnets.

We report the most stable surface of SmFe12 and the interface magnetic properties of SmFe12 with SmCu and bcc Fe as subphases. We find that the (110) surface with the highest exposition of Sm is the most stable surface of SmFe12. Stabilization by the exposition of rare-earth is also confirmed for Nd2Fe14B. Moreover, we also demonstrate that SmCu improves not only magnetic moments and the anisotropy of grain surfaces of SmFe12 but also well suppresses the magnetic interaction between SmFe12 grains.

We report the magnetism of fluorite Nd-Fe alloys containing 60-70 at% of Nd as a possible crystalline grain-boundary (GB) phase for Nd-Fe-B permanent magnets. Due to strong magnetic interactions between Nd and Fe, binary fluorite Nd-Fe alloys exhibit high Curie temperatures. The Curie temperature decreases significantly with the addition of Ga or Cu suggesting that these elements are indispensable for the demagnetization of the GB phase.