Many controversial and irreproducible results are reported for the giant magnetic moment of Fe 16N 2. This can be ascribed to the following facts: the sluggish dissociation of N 2 on Fe surface and accordingly low reactivity of N 2 with Fe at low temperatures, also that Fe 4N and other phases are much readily formed than Fe 16N 2, leading to the difficulty of the formation of single Fe 16N 2 phase. Even by plasma processes reported so far, the formation of single Fe 16N 2 phase seems difficult because quantitative kinetic data are strongly lacking. In this work, FeN x films were formed by an ion plating with an electron-beam evaporation process. Most films showed magnetic moments of up to M s = 1500 e.m.u. cm −3 (1.9 T), while a large magnetic moment of M s = 2025 e.m.u. cm −3 (2.54 T) was obtained for a thinner film. There, the reaction kinetics were clarified quantitatively from the viewpoint of gas-surface reactions. Conditions for FeN x film formation and their magnetic properties were discussed.