Magnetocaloric effect in large temperature window on off-stoichiometric Ni-Mn-Ga-based Heusler alloys

Abstract

Nickel-Manganese-Gallium-based Heusler alloys have been extensively studied for magnetic cooling applications with different compositions. However, the large hysteresis and narrow range of working temperatures associated with the first-order phase transition make limit their practical application. In this direction, the magnetocaloric effect was analyzed for three different off-stoichiometric compositions of Ni50+y+zMn25+x-yGa25‐x‐z alloys, where x, y, and z vary once at a time. Ni50Mn27Ga23 (NMG 1) and Ni54Mn21Ga25 (NMG 2) samples show large magnetocaloric effects across the second-order ferromagnetic to paramagnetic phase transition. Another sample Ni54Mn25Ga21 (NMG 3) undergoes coupled magneto-structural transition near room temperature with very low hysteresis loss (⁓4 J/kg) and a very high sensitivity of the martensite transition temperature (⁓3.6 K/T) with the field. By cyclic cooling protocol reliable magnetic entropy changes are found to be maxima of − 1.98 ± 0.09, − 1.90 ± 0.11 and − 3.53 ± 0.14 J/kg-K for 3 T field change with large effective RCP values of 235.8 ± 0.1, 161.5 ± 0.1 and 144.7 ± 0.3 J/kg for NMG 1, NMG 2 and NMG 3, respectively. The presence of inter-martensite transition along with the magnetic transition or magneto-structural phase transition widens the range of working temperature which effectively enhances the magnetic cooling performance of these materials. The TC and TM are tuned in Ni-Ga-Mn-based alloys by changing the chemical composition with considering the electron concentrations.