Ferromagnetism nitrides

Grinding and polishing is one of the oldest applications for wide band-gap materials primarily owing to the property of hardness that some of these materials possess (e.g., diamond). SiC and cubic boron nitride, in addition to diamond, have found a commercial market in grinding and polishing, primarily for ferromagnetic materials with high carbon solubility. 

Carbides and nitrides of Fe, Co, and Ni are ferromagnetic as their parent metals. The other compounds which are paramagnetic, show typically lower susceptibilities compared to the pure metals. 

As was pointed out by Yuan (1977) there is a distinct difference between the rare earth nitrides and the other pnictides because of the smallness of the nitrogen anion. In the nitrides the Ln-Ln distances are practically the same as in the trivalent metals. Therefore, direct exchange ( 1) will dominate here the superexchange ( 2) via the anions. Many of the rare earth nitrides are indeed ferromagnetic at low temperatures. 

For the magnetic structures of the nitrides of Tb Er a complicated retarded-spiral arrangement was proposed (Child et al., 1963). In the case of HoN, however, no long-range order appears to exist at all, but only a short-range ferromagnetic order (Fischer et al., 1976). 

Schlegel (1979) and Wachter and Kaldis (1980) prepared single crystals of stoichiometric gadolinium nitride and showed that GdN, contrary to the ferromagnetic semiconductor EuO, is a metamagnet with a 7n of 40 K, and that the carrier concentration at 300 K is 6% per Gd ion. 

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