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

The phase transition process and magnetic entropy change ΔSΔS of Ni54.5FeMn20Ga24.5Ni54.5FeMn20Ga24.5 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 ΔSΔS 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 ΔSΔS 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 ΔSΔS. The peak of negative ΔSΔS is -2.1J/kgK for a field change of 2 T.