Ab initiostudies of magnetic properties of cobalt and tetracobalt nitrideCo4N

Magnetic properties and bonding analyses of perovskite structure ${\mathrm{Co}}_{4}\mathrm{N}$ 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 ${\mathrm{Co}}_{4}\mathrm{N}$ 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 ${\mathrm{Co}}^{I}$ atoms show localized magnetism while face center ${\mathrm{Co}}^{II}$ atoms exhibit an itinerant behavior. Like in $\mathrm{fcc}\text{\ensuremath{-}}\mathrm{Fe}∕{\mathrm{Fe}}_{4}\mathrm{N}$, a ``low-volume--low-moment'' and ``large-volume--high-moment'' behavior is observed for $\mathrm{fcc}\text{\ensuremath{-}}\mathrm{Co}∕{\mathrm{Co}}_{4}\mathrm{N}$. The density of states of the ${\mathrm{Co}}_{4}\mathrm{N}$ ferromagnetic ground state is interpreted within the rigid band model. The different bonding characters of ${\mathrm{Co}}^{I}\ensuremath{-}\mathrm{N}$ versus ${\mathrm{Co}}^{II}\ensuremath{-}\mathrm{N}$ are shown with the help of electron localization function plots and spin resolved chemical bonding criteria.