Relations of electronic energies and magnetic moments of tetra-3d metal (Mn, Fe, Co and Ni) nitrides calculated using a plane-wave basis method

Geometrical optimization of tetra-3d metal nitrides (Mn₄N, Fe₄N, Co₄N, and Ni₄N) has been performed and the relations of their energies (E) and their total magnetic moments (M) are obtained by plane-wave-basis density-functional calculations without any assumption of specific spin arrangement. The E vs. M relations obtained for Fe₄N and Mn₄N have a bimodal character. The ground state of Fe₄N is a high-spin state, which would correspond to the ferromagnetic character, while that of Mn₄N is a low-spin state, which would correspond to the observed ferrimagnetic character. Lattice constants and total magnetic moments of these tetra-3d metal nitrides are almost accurately predicted. From the spin-polarized densities of states curves, Co₄N would have the largest spin polarization ratio of 0.88, which suggests Co₄N can be a candidate material for ferromagnetic electrodes for spin-injection.