The High Nitrogen Pressure Synthesis of Manganese Nitride

We report on the structural transformation and unique magnetic properties of manganese nitrides prepared by nitriding Mn under N₂ pressures of up to 25 MPa with varying temperatures. High N₂ pressure not only makes nitridation more efficient at lower temperatures, but also enhances the N-content in the nitride lattices, which were expanded with increasing N-content. The N-rich nitrides, including ε-Mn₄N, ζ-Mn₆N_2.58 and η-Mn₃N₂, exhibit unique thermal behaviors. The N-rich ε-phase exhibits much larger coercivity and lower saturation magnetization in comparison with the ε-phase prepared under ambient N₂ pressures. The coercivity of the N-rich ζ-phase reaches up to 45054 A/m. A saturation magnetization as large as 31 Am²/kg is observed in the N-rich η-phase. Both are quite different from the conventional antiferromagnetic ζ- and η-phase obtained under ambient N₂ pressures. We ascribe the unconventional magnetic properties of the nitrides to the lattice distortion originating from the N-enrichment.