Characterization of epitaxixally grown Fe-N films by sputter beam method

We have prepared epitaxial Fe-N martensite (α′) films on α-Fe (001) single-crystal underlayers by the sputter beam method and synthesized a metastable α″-Fe₁₆N₂ phase by post-annealing. The saturation magnetization (4πM_s) of the α′ phase films is in the range of 21.9-23.3 kGauss which is larger than that of α-Fe. Magnetization of the annealed samples containing α″-Fe₁₆N₂ phase have increased with the x-ray diffraction intensity ratio of α″(002) to [α″(004) + α′(002)]. Very careful analysis of x-ray diffraction data gives more reliable value on the volume fraction of the α″ phase in the annealed samples. As a result, it is found that the Fe-N film with magnetization of 24.7 kG contains 32 vol %-α″ phase within it. This result leads us to believe that α″-Fe₁₆N₂ phase has a remarkably large saturation magnetization.