Structure and magnetic moment of α″-Fe16N2 compound films: Effect of Co and H on phase formation (invited)

Abstract

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.