Composition adjustment and hydrostatic pressure control of magnetocaloric effect in Ni-Mn-Ga alloys [Ni-Mn-Ga合金磁热效应的组分调节与等静压调控]

作者：Hu F.-E.; Cao Y.-M.; Wei S.-X.^*; Tao C.; He X.-J.; Kang Y.-R.; Li Z.

来源：Chinese Journal of Nonferrous Metals, 2019, 29(12): 2793-2801.

DOI：10.19476/j.ysxb.1004.0609.2019.12.12

• Hydrostatic pressure
• Magnetic refrigeration
• Magnetocaloric effect
• Martensitic transformation
• Ni-Mn-Ga alloy

The optimization, regulation and control of magnetocaloric effect (MCE) in Ni-Mn-Ga alloys are one of the main research hotspots in refrigeration engineering. In order to optimize the MCE of Ni-Mn-Ga alloys, the phase transformation properties and the effects of composition and hydrostatic pressure on MCE in Ni54+xMn19-xGa27 (x=0.0, 0.4, 1.0) were experimentally studied and discussed. The results from heat flow data and magnetic measurements show that the martensitic transformation (MT) temperatures gradually increase with increasing the Ni content. However, the Curie temperatures first decrease and then increase with increasing Ni content. Importantly, a first-order coupled magnetic-structural transformation (MST), i.e., a simultaneous occurrence of the first-order MT and of the second-order magnetic transition, is observed in Ni-Mn-Ga alloys with x=1.0. Besides, absolute value of the maximum magnetic entropy changes (ΔSMmax) and refrigeration capacity (WRC) increases with the Ni content increase under the same magnetic field change. Furthermore, ΔSMmax and WRC are as large as 8.2 J/(kg?K) and 53.61 J/kg for the alloy with x=1.0 under a magnetic field change of 3 T. Such values in ΔSMmax are approximately 3.04 and 2.28 times of those of alloys with x of 0 and 0.4, respectively. Meanwhile, the amplitude of WRC for x=1.0 are about 3.31 and 1.67 times of those of alloys with x of 0 and 0.4, respectively. Much importantly, the hydrostatic pressure of 0.58 GPa has a marginal effect on ΔSMmax in the alloy with x=1.0 while WRC is enhanced by 43.82% resulting from the application of hydrostatic pressure to broaden the temperature window of phase transformation. For the sake of comparison and engineering application, the dependence of the external magnetic field on ΔSMmax and WRC is obtained by using the linear fitting method. These relationships can be used to rapidly estimate ΔSMmax and WRC in Ni54+xMn19-xGa27 (x=0.0, 0.4, 1.0) alloys under various magnetic fields. The results are very meaningful for the optimization, adjustment and control and engineering application of magnetocaloric effect in Ni-Mn-Ga alloys.