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 ?-Mn4N, ?-Mn6N2.58 and ?-Mn3N2, exhibit unique thermal behaviors. The N-rich ?-phase exhibits much larger coercivity and lower saturation magnetization in comparison with the ?-phase prepared under ambient N2 pressures. The coercivity of the N-rich ?-phase reaches up to 45054 A/m. A saturation magnetization as large as 31 Am2/kg is observed in the N-rich ?-phase. Both are quite different from the conventional antiferromagnetic ?- and ?-phase obtained under ambient N2 pressures. We ascribe the unconventional magnetic properties of the nitrides to the lattice distortion originating from the N-enrichment.