Structure and magnetic properties of iron nitride films prepared by reactive dc magnetron sputtering

We have investigated the structure and magnetic properties of iron nitride films prepared by reactive dc magnetron sputtering with an argon gas flow rate of 12 sccm and a nitrogen gas flow rate varied between 0-10 sccm. Under the above conditions, the nitrogen concentrations in the iron nitride films were changed from 0 to 33 at.%. The phase and structure of the films changed from α-Fe, amorphous matrix with nanocrystallites of ε-Fe₃N, ε-Fe_xN (2 < x ≤ 3) to ζ-Fe₂N phase as the nitrogen concentration of the iron nitride films increases, and these changes in the phase almost correspond to the Fe-N phase diagram. The saturation magnetization of the iron nitride films decreases as the nitrogen concentration increases up to 31 at.%, and disappears at 33 at.%. A relatively low coercivity of 9 Oe is observed at the nitrogen concentrations from 11 to 18 at.%. From the results of structural analysis and magnetic measurements, it is confirmed that the coercivity of the iron nitride films mostly correlates with the changes in grain size.