Magneto-structural transitions driven giant magnetocaloric effect in Ni42Mn43Cr4Sn11 Shape Memory Heusler Alloy near room temperature

In the current work, a Ni-Mn-X (X = Sn, In) type off-stoichiometric, polycrystalline magnetic shape memory alloy (MSMA) having nominal composition Ni42Mn43Cr4Sn11 (at. %) has been thoroughly investigated in terms of its crystal structure, microstructure, magnetic properties, and magnetocaloric effect (MCE). X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), differential scanning calorimetry (DSC), and magnetic and magneto-transport measurements are used to characterize it. By offering a significant value of parameters related to MCE at the first-order martensite transition (FOMT) and the secondorder magnetic transition (SOMT), the Cr doping at the Ni site enables considerable magnetic refrigeration to occur close to room temperature (RT). The alloy crystallises into coexisting cubic L21 austenite and tetragonal L10 martensite phases, among which the first one prevails as the leading phase at room temperature (RT) without exhibiting any geometric frustration. Lattice strain is enumerated using the Williamson-Hall method. A huge working temperature spans of 29.65 K and 26.16 K; the maximum magnetic entropy changes of +8.70 J kg-1.K-1 and -5.04 J kg-1.K-1 and the maximum refrigerant capacities (RC) of 284.24 J. Kg-1 and 234.10 J. Kg-1 across FOMT and SOMT, respectively at an applied magnetic field of 6 T are found to be most suitable for real technological applications. This MSMA offers a comparatively low cost of the constituent elements (Ni, Mn, Cr, and Sn), as well as exhibits giant MCE and RC across both FOMT and SOMT, making it an excellent candidate for magnetic refrigeration near RT. It also opens up new avenues for future research on novel Heusler alloys of this type.

Automated summary

In this study, a Ni-Mn-X (X = Sn, In) type off-stoichiometric, polycrystalline magnetic shape memory alloy (MSMA) with nominal composition Ni42Mn43Cr4Sn11 (at. %) was thoroughly investigated. The alloy exhibited significant magnetic refrigeration properties close to room temperature due to doping with Cr at the Ni site. It crystallized into coexisting cubic L21 austenite and tetragonal L10 martensite phases, with the former being the dominant phase at room temperature. The alloy showed a wide working temperature range, large magnetic entropy changes, and high refrigerant capacities, making it a promising candidate for magnetic refrigeration applications near room temperature and opening up new research avenues for Heusler alloys of this type.