(1. 曲靖师范学院 磁性材料及器件研究中心，曲靖 655011；
2. 曲靖师范学院 化学与环境科学学院，曲靖 655011；
3. 曲靖师范学院 物理与电子工程学院，曲靖 655011)
摘 要: Ni-Mn-Ga合金磁热效应的优化是制冷工程的研究热点之一。为深入研究Ni-Mn-Ga合金的磁热效应，以Ni54+xMn19-xGa27 (x=0、0.4、1.0，摩尔分数)为研究对象，利用实验手段研究了合金的相变特性、组分及等静压对合金磁热效应的优化与调控作用。结果表明：随着Ni含量的增加，Ni54+xMn19–xGa27合金的马氏体相变温度逐渐升高，而居里温度则先减小再增大；当x=1.0时，合金出现了磁-结构相变。相同外加磁场时，合金的最大磁熵变的绝对值(|ΔSM|max)及制冷量(WRC)随Ni含量的增加而增大。当磁场改变3 T时，合金x=1.0对应的|ΔSM|max和WRC最大、约为8.2 J/(kg·K)和53.61 J/kg，分别是x为0、0.4的3.04、2.28倍与3.31、1.67倍。0.58 GPa等静压对合金x=1.0的|ΔSM|max影响可忽略不计，但等静压的应用有利于拓宽合金的相变温区、致使合金WRC提高了43.82%。为便于比较和工程应用，给出了合金|ΔSM|max、WRC与外加磁场H的依赖关系。研究结果为Ni-Mn-Ga合金磁热效应的优化、调控及工程应用具有较好的指导意义。
关键字: Ni-Mn-Ga合金；磁制冷；马氏体相变；磁热效应；等静压
（1. Center for Magnetic Materials and Devices, Qujing Normal University, Qujing 655011, China ;
2. College of Chemistry and Environmental Science, Qujing Normal University, Qujing 655011, China;
3. College of Physics and Electronic Engineering, Qujing Normal University, Qujing 655011, China）
Abstract: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 (|ΔSM|max) and refrigeration capacity (WRC) increases with the Ni content increase under the same magnetic field change. Furthermore, |ΔSM|max 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 |ΔSM|max 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 |ΔSM|max 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 |ΔSM|max and WRC is obtained by using the linear fitting method. These relationships can be used to rapidly estimate |ΔSM|max 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.
Key words: Ni-Mn-Ga alloy; magnetic refrigeration; martensitic transformation; magnetocaloric effect; hydrostatic pressure
