0 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-principle TB-LMTO-ASA method. Among all the FeN phases considered, the antiferro-magnetic (AFM) NaCl structure with q = (0, 0, π) is found to have the lowest energy at the theoretical equilibrium volume. However, the ferromagnetic (FM) NaCl phase lies only 1mRy higher. The estimated equilibrium lattice constant a th =4.36Å for nonmagnetic (NM) ZnS-type FeN agrees quite well with the experimental value of a exp =4.33Å but for AFM NaCl phase the a th =4.20Å is 6.7% smaller than the value observed experimentally. For ZnS-type FeN, metastable magnetic states are found for volumes larger than the equilibrium value. With the analysis of atom-and orbital-projected density of states (DOS) and orbital-resolved crystal orbital Hamilton population (COHP) 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 all three phases. The iron magnetic moment µ F e in FeN is found to be highly sensitive to the nearest-neighboring Fe-N distance. In particular, the µ F e in ZnS and CsCl structures show an abrupt drop from the value of about 2µ B to zero with the reduction of the Fe-N distance.