Martensitic and magnetic transformations of Ni–Ga–Fe–Co ferromagnetic shape memory alloys

Effects of Co addition on the phase equilibria between the β (B2) and γ (A1) phases at 800 and 1000 °C and aging temperature dependence on the martensitic and magnetic transformation temperatures in Ni–Ga–Fe–Co alloys were examined with energy dispersion X-ray spectroscopy (EDX), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). The equilibrium compositions of Fe and Ga are little changed by the addition of Co, and Co tends to be distributed in the γ phase rather than in the β phase. The B2/L21 order–disorder and magnetic transformation temperatures increase with increasing Co content, while the martensitic transformation temperatures decrease. While the martensitic transformation temperatures monotonously decrease with decreasing aging temperature, the Curie temperature increases with the decrease of aging temperature in the high temperature region over 300 °C and then starts to decrease at low temperatures.