Influence of nitrogen dopants on the magnetization of Co3N clusters

Using a real-space implementation of pseudopotentials within the density-functional theory, we show that the magnetization of a ${\mathrm{Co}}_{3}\mathrm{N}$ cluster with a recently discovered atomic structure is significantly affected by nitrogen dopants. In a ${\mathrm{Co}}_{3}\mathrm{N}$ cluster with the hexagonal $P{6}_{3}/mmc$ structure, N dopants promote spin polarization for the Co-$3d$ electrons and the dopants themselves make additional contributions to net magnetic moment. These two factors enhance the total magnetic moment of a hexagonal ${\mathrm{Co}}_{3}\mathrm{N}$ cluster, which can be as strong as bulk iron. In contrast, N dopants in a ${\mathrm{Co}}_{3}\mathrm{N}$ cluster with the rhombohedral $R\overline{3}c$ structure degrade magnetic moment and the dopants are magnetically ``inert,'' which results in lower total magnetic moments in rhombohedral ${\mathrm{Co}}_{3}\mathrm{N}$ clusters. These changes in magnetic moment originate from differences in the orbital hybridization between the Co-$3d$ and N-$2p$ states. We also examine how the magnetization of a ${\mathrm{Co}}_{3}\mathrm{N}$ cluster depends on a N content. We find that the total magnetic moment of a hexagonal ${\mathrm{Co}}_{3}{\mathrm{N}}_{1+x}$ cluster with $\ensuremath{-}0.15\ensuremath{\le}x\ensuremath{\le}0.15$ is tunable and can be enhanced further by controlling the amount of nitrogen dopants.