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, Fe4N are more stable compared to Fe and N-2 gas. Ni4N may be a metastable phase since mixture of Ni3N and Ni would be more energetically stable. Fe4N 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 Fe3N must be evaluated so as to make precise evaluation, which is beyond the scope of the present work. Co4N 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 Fe8N with the alpha ''-Fe16N2 type structure would be stable among octa-metal nitrides with the assumed structure of the alpha ''-Fe16N2 type and the Ni32N4 type structure. All of Fe3N, Co3N, and Ni3N are stable, but Ni3N would be non-magnetic in contrast to ferromagnetism of other tri-metal nitrides. (C) 2014 Elsevier B.V. All rights reserved.