In order to make a comparison with -gas nitrogenation, the structural and magnetic properties of ammonia-nitrided were investigated by a combination of x-ray diffraction, magnetization and nuclear magnetic resonance. It was found that by using , the nitrogenation temperature and/or time are greatly reduced, and nominal N concentrations are obtainable. For lower N content, , a two-phase (nitrided + unnitrided) configuration exists in the sample particles. The unnitrided phase is completely suppressed for ; however, an amorphous-like phase appears for . The average value for the magnetic moment per Fe atom initially increases with the N content, reaching a maximum for before decreasing. The magnetic anisotropy, which arises solely from the Fe sublattice, is reduced for higher N content, but is still basal planar. These results indicate that the microscopic structure of the nitrided phase in ammonia-nitrided is different from that in the same material prepared by -gas nitrogenation. Evidence is provided for the existence of more than three, most likely four, nitrogen atoms per formula unit in the nitrided phase when x > 3.