Influence of nitrogen dopants on the magnetization of cobalt-nitride clusters*

Using a real-space pseudopotential approach within the density-functional theory, which is implemented in the PARSEC code, we show that the magnetization of a cobalt-nitride cluster is significantly affected by nitrogen dopants. In particular, we focus on Co₃N clusters with recently-discovered hexagonal P6₃/mmc and rhombohedral R-3c structures. In a hexagonal Co₃N cluster, N dopants promote spin polarization for the Co–3d electrons, leading to a large total magnetic moment, which can be as strong as bulk iron. In contrast, N dopants in a rhombohedral Co₃N cluster degrade magnetic moment and the dopants are magnetically ``dead,'' which results in lower total magnetic moments in rhombohedral Co₃N clusters. These changes in magnetic moment originate from the difference in an orbital hybridization between the Co–3d and N–2p states. We also examine how the magnetization of a Co₃N cluster depends on a N content. We find that the total magnetic moment of a hexagonal Co₃N_1+x cluster with -0.15 < x < 0.15 is tunable and can be enhanced further by controlling the amount of nitrogen dopants.