Proposed Compositions in a Ni-Mn-Ga System for Magnetocaloric Applications

Magnetocaloric materials (MCM) have garnered significant attention within the research community, as they can minimize the use of harmful gases such as chlorofluorocarbons and hydrofluorocarbons, and provide eco-friendly refrigeration. Heusler alloys (Ni2MnGa) are known for their magnetocaloric effects, which make them useful as energy-efficient and eco-friendly refrigerating materials. Magnetocaloric properties depend significantly on the composition of these alloys. Ni-Mn-Ga is an interesting Heusler system which exhibits magnetocaloric properties. In the present study, we performed thermodynamic optimization of two sub-binaries of the Ni-Mn-Ga system, Mn-Ga and Ni-Ga, using the CALPHAD approach. Both binaries were combined with Mn-Ni to develop a self-consistent thermodynamic database for Ni-Mn-Ga. In order to resolve the existing experimental discrepancies in the Mn-Ga and Ni-Ga system, a few alloy compositions were prepared and analysed using differential thermal analysis. Finally, the developed thermodynamic database was used to calculate the T0 (K) or the martensite start temperature. The influence of varying Mn, Ni, and Ga concentrations on T0 (K) is discussed using the hybridization theory, and the current calculation results are compared with previous experiments in the literature. Lastly, a few compositions in the Mn-rich region are proposed which exhibit comparable or better magnetocaloric properties relative to the existing alloys.