Abstract

Two Ni–Mn–Sn alloys substituted with 0.5 and 1 at.% Cr have been studied. The first alloy shows an average composition of Ni_49.6Mn_37.3Cr_0.7Sn_12.4 (e/a = 8.107), whereas the second has a multiphase microstructure with the matrix phase of an average Ni_52.4Mn_32.7Cr₁Sn₁₄ composition (e/a = 8.146). Both alloys undergo a reversible martensitic phase transformation. The Ni_49.6Mn_37.3Cr_0.7Sn_12.4 alloy transforms to the martensite phase at 239 K and, under the magnetic field change of μ₀·ΔH = 1.5 T, gives the magnetic entropy change equal to 7.6 J/kg·K. This amounts to a refrigerant capacity in the order of 48.6 J/kg, reducible by 29.8% due to hysteresis loss. On the other hand, the alloy with a multiphase microstructure undergoes the martensitic phase transformation at 223 K with the magnetic entropy change of 1.7 J/kg·K (1 T). Although the latter spreads over a broader temperature window in the multiphase alloy, it gives much smaller refrigerant capacity of 16.2 J/kg when compared to Ni_49.6Mn_37.3Cr_0.7Sn_12.4. The average hysteresis loss for a field change of 1.5 T in the multiphase alloy is 2.7 J/kg, reducing the effective refrigerant capacity by 16.7%. These results illustrate that the key to gaining a large effective refrigerant capacity is the synergy between the magnitude of the magnetic entropy change and its broad temperature dependence. View Full-Text