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

Change in entropy (Delta S) 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 Delta S. Delta S can be estimated from differential scanning calorimeter curves. Magnetic characterization reveals that the magnetic contribution Delta S-M, is dominant contributor to Delta S. Delta S-M, 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 AS and Delta S-M in a variety of promising FSMAs provides a means to identify alloys suitable for applications such as magnetic sensors, actuators and magnetic refrigeration. (C) 2014 Elsevier B.V. All rights reserved.