Abstract
Foils of the γ-FeN phase were prepared by the conventional gas nitrification method in an NH3 + H2 atmosphere. We found the γ-FeN phase field extends beyond 11.1 at%N at 660°C, which is the stoichiometric composition of Fe16N2. The γ-FeN phase with 9.8 at%N is transformed into a mixture of the α' and γ phases by cooling to below 180 K. An intense external magnetic field at 4.2 K is found to drive the martensitic transformation occurring in the γ phase, and a field of 170 kOe reduces the amount of residual γ phase from 38% to 16%. This results in a drastic increase in the spontaneous magnetization from 147 emu/g to 198 emu/g.
