Estimation of entropy change at the first order martensitic transition in Ni–Mn–X based ferromagnetic shape memory alloys

Abstract

Change in entropy (ΔS) has been estimated at the first order martensitic transition in selected Ni–Mn–X (Ga, Sn, and In) based ferromagnetic shape memory alloys (FSMAs). During the first-order martensitic structural phase transition, discontinuity in entropy leads to a large ΔS. ΔS can be estimated from differential scanning calorimeter curves. Magnetic characterization reveals that the magnetic contribution ∆SM, is dominant contributor to ΔS. ∆SM is also responsible for the giant magnetocaloric effect observed in these FSMAs. By controlling the valence electron to atom ratio (e/a), it is possible to realize a large entropy change near ambient temperature in these alloys. Estimation of ∆S and ∆SM in a variety of promising FSMAs provides a means to identify alloys suitable for applications such as magnetic sensors, actuators and magnetic refrigeration.