Curie temperature effect on the inverse MCE in Ni2MnIn based Heusler alloys near room temperature

We investigate the magneto caloric properties in Ni2MnIn based Heusler alloys having the martensitic to austenitic transition temperatures close to the Curie temperature of the austenitic phase. We tuned the structural transition by composition in order to encounter three possible cases as a function of the increasing temperature: I) the martensite to austenite transition completes before the drop of magnetization associated to the Curie temperature of the austenite, ii) the martensite to austenite transition evolves across the Curie temperature of the austenite and iii) the martensite to austenite transition lies almost completely above the Curie transition of the austenite. When the martensitic transition temperature overlaps with the Curie temperature of the austenite we observe, at constant temperature, the coexistence of direct and inverse magneto caloric effects. In order to understand this behaviour we design a layered structure composed by a 1st order inverse MC material and a 2nd order direct MC material. In this structure, part of the heat exchanged by the direct MCE cooperates with the magnetic field to drive the structural transition further.