Synthesis of iron nitrides FexN (x: 2, 2-3, 4, 16/2) by nitrogenizing α-Fe ammonia gas, and magnetic properties of the bulk sample of Fe16N2

Abstract

Iron nitrides were prepared by nitrogenizing α-iron in ammonia gas at temperatures from 100°C to 700°C. In the case using iron foils as a starting material, Fe2-3N and Fe4N were formed as a main crystal phase at the temperature ranges of 450-700°C and 250-400°C, respectively. A crystal phase like to Fe16N2 was formed at 210°C, but its XRD and Mossbauer data were too insufficient to identify as Fe16N2. While bulk Fe16N2 was formed by nitrogenizing iron fine powder with the diameter of about 20nm at 110°C for 10 days, but small amounts of Fe3N coexisted as a second phase with Fe16N2 at 120°C for 10 days. Crystal structure of Fe16N2 was refined by Rietveld method. The average magnetic moment of three kinds of Fe atoms in Fe16N2 was evaluated to be 2.52μB on the basis of its Mossbauer data, the value of which was larger by 15% than the magnetic moment of α-Fe. The saturation magnetization of the Fe16N2 powder was also larger by about 14% than that of the α-Fe powder before nitrogenizing.