Phase transformation and magnetic properties in Ni–Mn–Ga Heusler alloys

Ni-rich ferromagnetic Ni–Mn–Ga Heusler alloys were investigated for structural and magneto-caloric effect. The structural transition from austenite to martensite near room temperature was observed with the increase of Ni content. The saturation magnetization measured at room temperature decreased with the increase of Ni content. A large change in magnetization (32%) was observed even for a small increase in Ni concentration (12%). The martensitic transition temperature (TM) and Curie temperature (TC) of all the samples were studied using thermo-magnetic as well as differential scanning calorimetry (DSC) techniques. The martensite and the magnetic transitions were found to be sensitive to the composition and were tuned through alloy composition to occur simultaneously at near room temperature. A change in magnetic entropy, (ΔS)M of −0.68 J/kg K was determined in Ni55Mn20Ga25 for which TM and TC were close to room temperature.