Electronic structure and magnetism of equiatomic FeN

In order to investigate the phase stability of equiatomic FeN compounds and the structure-dependent magnetic properties, the electronic structure and total energy of FeN with NaCl, ZnS and CsCl structures and various magnetic configurations are calculated using the first-principles TB-LMTO-ASA (tight-binding linear muffin-tin orbitals within the atomic sphere approximation) method. Among all the FeN phases considered, the antiferromagnetic (AFM) NaCl structure with q = (0, 0, pi) is found to have the lowest energy at the theoretical equilibrium volume. However, the ferromagnetic (FM) NaCl phase lies only I mRyd higher. The estimated equilibrium lattice constant a(th) = 4.36 Angstrom for non-magnetic (Nhl) ZnS-type FeN agrees quite well with the experimental value of a(exp) = 4.33 Angstrom but for the AFM NaCl phase the value a(th) = 4.20 Angstrom is 6.7% smaller than the experimentally observed 4.50 Angstrom. For ZnS-type FeN, metastable magnetic states are found for volumes larger than the equilibrium value. On the basis of an analysis of the atom-and orbital-projected density of states and orbital-resolved crystal orbital Hamilton population, the iron-nitrogen interactions in NM ZnS, AFM NaCl and FM CsCl structures are discussed. The leading Fe-N interaction is due to the d-p iron-nitrogen hybridization, while considerable s-p and p-p hybridizations are also observed in an three phases. The iron magnetic moment mu(Fe) in FeN is found to be highly sensitive to the nearest-neighbouring Fe-N distance. In particular, the mu(Fe)-value shows an abrupt drop from a value of about 2 (mu B) to zero with the reduction of the Fe-N distance for the ZnS and CsCl structures.