Neutron study of the martensitic transformation in Ni-Fe-Ga alloys

We present results of an extensive neutron diffraction study of the martensitic transformation in Shape Memory Alloys of nominal composition Ni55-xFe19+xGa26 (x=0, 1, 2) at. % transforming close to room temperature. The x=0 sample shows a martensitic transformation temperature T-M approximate to 250 K and Curie temperature T-C approximate to 289 K. Neutron measurements for this alloy were performed between 300 K (austenite phase) and 150 K (martensitic phase). At temperatures T > T-C we have found the coexistence of two phases: an L2(1) phase with space group Fm3m and cell parameter a=5.730A and a gamma-fcc with cubic symmetry and with cell parameter a=3.586A This second phase was also detected by magnetic measurements, giving rise to a second Curie temperature of about 363 K.