Negative and positive magnetocaloric effect in Ni–Fe–Mn–Ga alloy

Abstract

The phase transition process and magnetic entropy change Δ S of Ni 54.5 FeMn 20 Ga 24.5 alloy were studied. Substitution of Fe for Ni increases the Curie temperature and decreases the temperature of martensitic phase transition. The transition from ferromagnetic martensitic to ferrormagnetic austenitic state leads to an abrupt increase of magnetization below 0.5 T and an abrupt decrease of magnetization above 0.5 T. The sign of Δ S changes from positive to negative with increasing the applied field from 0.5 to 2 T. The maximal value of the positive magnetic entropy change Δ S is about 3.1 J/kg K for the applied field from 0 to 0.5 T. The increase of applied field from 1.5 T results in a negative Δ S . The peak of negative Δ S is - 2.1 J / kg K for a field change of 2 T.