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In order to determine the value of the intrinsic magnetic moment of the α ″ phase, the films of nitrogen-martensite with various N content were fabricated under various reactive sputtering conditions. The magnetic moment of (α ″+α′)-Fe16N2 films is discussed in connection with the change of the unit-cell volume of the bct structure and the degree of N site ordering in nitrogen-martensite. As a result, it is found that (1) the same structure as bulk α ″-Fe16N2 is realized in the present films, (2) the saturation magnetization σs of the α′ phase increases about 4% with increasing unit-cell volume of the α′ phase, (3) the degree of N site ordering from α′ to α ″-Fe16N2 does not much affect σs, and (4) the experimentally obtained maximum value of σs for the (α ″+α′)-Fe16N2 film was 232 emu/g. The intrinsic value of σs in the α ″ phase (in the perfectly ordered state) is proposed to be no more than 240 emu/g at 300 K.

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In order to determine the intrinsic value of magnetic moment, σs, of α″-Fe16N2 compound, the magnetic moment of (α″+α′)-Fe16N2 films is discussed in connection with the degree of N site ordering in nitrogen–martensite. To establish the more general relation between Fe–N martensite structure and σs, the Fe–N system is expanded to Fe–Co–N and Fe–H–N systems. As a result, it is found that (1) The existence of completely the same structure as bulk α″ phase was reconfirmed even in the film form by the precise structural analysis using x-ray diffraction, transmission electron microscopy and Mössbauer analysis, (2) Fe–H martensite was synthesized by using sputtering under Ar+H2 atmosphere, (3) Stable formation of α″-(Fe100−XCoX)16N2 (X=10–30) phase through N site ordering by postannealing is proposed to be fairly difficult due to the sudden decrement of the phase decomposition temperature, Tp.d., of α′-(Fe100−XCoX)–N (X=0–30). Tp.d. of α′-(Fe100−XCoX)–N (X=0–30) phase decreases from 200 °C to RT with increasing Co and N contents, and (4) The intrinsic value of saturation magnetization of the α″-Fe16N2 phase is convinced to be no more than 240 emu/g (≊2.4 μB per Fe atom on average) at 300 K.