Ab initio studies of magnetic properties of cobalt and tetracobalt nitride Co4 N

Magnetic properties and bonding analyses of perovskite structure Co4 N nitride have been investigated within density functional theory using both pseudopotential and all electron methods. In the same time, the structural and magnetic stabilities of pure cobalt in hexagonal close packed (hcp), face centered cubic (fcc), and body centered cubic structures are reviewed. At equilibrium, non-spin-polarized and spin-polarized calculations of the energy versus volume show that the ground state is ferromagnetic in both materials. hcp-Co is found to be more stable than the cubic ones. Magnetic moments of Co atoms in Co4 N nitride, respectively, belonging to two different crystallographic sites are studied over a wide range of the cubic lattice constant, and a comparison with the fcc-cobalt one is given. The volume expansion in the nitride indicates that the corner CoI atoms show localized magnetism while face center CoII atoms exhibit an itinerant behavior. Like in fcc-Fe/Fe4 N, a "low-volume-low-moment" and "large-volume-high- moment" behavior is observed for fcc-Co/Co4 N. The density of states of the Co4 N ferromagnetic ground state is interpreted within the rigid band model. The different bonding characters of CoI -N versus CoII -N are shown with the help of electron localization function plots and spin resolved chemical bonding criteria. © 2007 The American Physical Society.