Martensitic transformation in Ni–Fe–Ga alloys

Fe-based ferromagnetic shape memory alloys have attractive mechanical properties as compared with the classical Ni2MnGa ones, because of their enhanced ductility. This opens new possibilities regarding technical applications as magnetic sensors or actuators. In this work, we present a multiple technique study of the martensitic transformation in alloys with nominal composition Ni55−xFe19+xGa26 (x = 0, 1, and 2) transforming close to room temperature. Magnetic characterisations, performed in a SQUID magnetometer and by AC methods show the Curie temperature (TC ≈ 300 K) increasing with Fe content while the martensitic temperature (TM ≈ 240 K) decreases, in agreement with DSC and resistivity measurements. In addition, several Curie temperatures are found by the magnetic measurements, indicating the coexistence of different phases in the alloy. Neutron diffraction study suggests the L21-ordered cubic phase for austenite and 14 M structure for the martensitic phase. The transformation is observed from the temperature evolution of the diffraction peaks.