Investigation of Magnetic Field-Induced Phase Transition in Ni50Mn28Ga22, a Ferromagnetic Shape Memory Alloy

Ferromagnetic shape memory alloys (FSMAs) exhibit magnetic-field-induced strain (MFIS) through a reversible martensitic transformation. Among these, Nickel-Manganese-Gallium has drawn significant attention due to their large MFIS (up to ~10% in single crystals), far surpassing the best magnetostrictive materials such as Terfenol. Such a large axial strain change in single-crystal Ni-Mn-Ga arises from a coupled structural and magnetic phase transition. This enables rapid, reversible deformation without mechanical loading, making these materials promising for compact actuators, sensors, and energy harvesters. Their transition temperatures and magnetic properties are tunable via composition, offering flexibility for several device applications. Our research focuses on the investigation of Ni50Mn28Ga22 for the development of a core-shell structure with the MFIS materials as a core and piezoelectric material as the shell for potential biomedical applications. As a first step, we purchased 2 samples of Ni₅₀Mn₂₈Ga₂₂ FSMAs from 2 independent vendors and investigated their magnetic and magnetostrictive properties. Magnetization vs. tempeature graphs at different applied magnetic fields and hysteresis graphs at 275K for both samples, were measured. The MT graphs show that there is a first-order-like phase transition at 300K for applied field from 0 to 0.6T. The phase transition then changes to a second-order-like broader phase transition from 0.6T to 9T. There is a structural phase transition between a high temperature austinite phase and a low temperature martensite phase around 300K however, both martensite (measured at 275K) and austinite (measured at 300K) show hysteretic ferromagnetic behaviour indicating that the structural phase transition is not accompanied by a magnetic phase transition but a change is their relative permeability/susceptibility. A large strain change is observed while cycling through the phase transition temperature, in both heating and cooling curves. A magnetostrictive-like strain is also observed with the magnetic field however, the magnetic field-induced phase transition was not observed experimentally in either samples.