Energetic stability and magnetic moment of tri-, tetra-, and octa- ferromagnetic element nitrides predicted by first-principle calculations

Formation energies and magnetic moments of tri-, tetra-, and octa- ferromagnetic element nitrides have been calculated using spin-polarized Perdew–Wang generalized gradient approximations of the density functional theory. From the energetic point of view, Fe 4 N are more stable compared to Fe and N 2 gas. Ni 4 N may be a metastable phase since mixture of Ni 3 N and Ni would be more energetically stable. Fe 4 N may be also a metastable from energetic point of view but effect of configurational entropy caused by N-vacancy and of disregarded random occupation of interstitial sites by N observed in Fe 3 N must be evaluated so as to make precise evaluation, which is beyond the scope of the present work. Co 4 N are not stable compared to Co metal with the hcp structure and N 2 gas, but more stable in case Co metal with the fcc structure is used as a reference state. Only Fe 8 N with the α″-Fe 16 N 2 type structure would be stable among octa-metal nitrides with the assumed structure of the α″-Fe 16 N 2 type and the Ni 32 N 4 type structure. All of Fe 3 N, Co 3 N, and Ni 3 N are stable, but Ni 3 N would be non-magnetic in contrast to ferromagnetism of other tri-metal nitrides.