Research and development of rare earth-iron interstitial compounds

In 1990, the discovery of interstitial nitrogen atom effect on rare earth-iron intermetallics attracted much interest in the field of magnetism and magnetic materials. The nitrogenation effect is typically demonstrated in 2:17 and 1:12 rare earth - iron compounds. After nitrogenation, the intrinsic magnetic properties of the 2:17 and 1:12 nitrides are marvelously improved. So their intrinsic magnetic properties are comparable to those of Nd₂Fe₁₄B, even better in terms of Cuire temperature and corrosion resistance^[1-2]. At the same time, neutron diffraction studies indicated that after nitrogenation, the 2:17 and 1:12 nitrides remain their original crystal structure. The nitrogen atoms occupy definite interstitial sites. On the basis of neutron diffraction data, theoretical calculations showed that the nitrogen atoms located at the interstitial sites effectively modify the crystal field interaction of 4f electrons of rare earth atoms, as well as the 3d electronic structures of iron atoms. All the modifications by interstitial nitrogen atoms result in a fundamental change in the magneto-crystalline anisotropy of rare earth atoms, and an increase in magnetic moment of iron atoms as well as a significant enhancement for Fe-Fe exchange interactions. As a result, in the rare earth material´s family, a new series of rare earth-iron intermetallics with outstanding intrinsic magnetic properties were found based on the interstitial nitrogen atom effect, which was named as interstitial compounds^[3-4]. Since then a quarter of a century has passed, tireless effort has been made in the world wide to bring the interstitial compounds into commercial use. Up to date, a variety of materials has been developed not only for the applications in the field of permanent magnets but also for the microwave absorbers based on the interstitial compounds.