Magnetic and martensitic phase transitions in ferromagnetic Ni–Ga–Fe shape memory alloys

Ferromagnetic shape memory alloys with a body-centered-cubic ordered structure in a Ni–Ga–Fe system have been developed. The alloys with the composition range of Ni 27 at. % Ga (20–22 at. %)Fe exhibit a thermoelastic martensitic transformation from a B2 and/or an L21 parent to a martensite phase, with a seven-layer modulated (14M) and a five-layer modulated (10M) structure, in the ferromagnetic state. The parent phase transforms from the B2 to the L21 structure at about 970 K during cooling, and the degree of the L21 order in the parent phase is increased by annealing at 773 K, resulting in the increase of both the martensite starting and the Curie temperatures. The ductility of these alloys is improved by introducing of a small amount of a γ-phase solid solution. Consequently, we can conclude that the present alloys are promising for ferromagnetic shape memory alloys.