Proposed compositions in Mn-Ni-Cu system for magnetocaloric application using a combination of thermodynamic modeling and experiments

Magnetic refrigeration is an active research area considering its potential to replace gas-based refrigeration systems, which are detrimental to the environment owing to chlorofluorocarbon emissions. Heusler alloys such as Ni2MnGa are known for their magnetocaloric effect, and addition of elements like Cu has increased the refrigeration capacity of the system. Magnetocaloric properties are a strict function of composition, and few alloy compositions in Mn-Ni-Cu-Ga can exhibit enhanced magnetocaloric properties. Most of the previous works have focused on Mn-Ni-Cu-Ga, and the enhancement of magnetocaloric properties is attributed to adding Cu. However, no magnetocaloric material has been reported in the Mn-Ni-Cu system, which could potentially show benefit from Cu addition. Hence, in the present study, thermodynamic optimization of the Mn-Ni-Cu-based ternary system and its three sub-binaries, Mn-Cu, Mn-Ni, and Ni-Cu, are performed using the CALculation of PHAse Diagram approach. In order to capture the liquidus in the Mn-Ni system and congruent transformation, a few alloy compositions were prepared and analyzed using differential thermal analysis. Using the current optimized database, temperatures are calculated as a function of Mn, Ni, and Cu compositions to ascertain the phase transition between the austenite and martensite phases, which occur around room temperature.