(1. 曲靖師范學(xué)院 磁性材料及器件研究中心，曲靖 655011；
2. 曲靖師范學(xué)院 化學(xué)與環(huán)境科學(xué)學(xué)院，曲靖 655011；
3. 曲靖師范學(xué)院 物理與電子工程學(xué)院，曲靖 655011)
摘 要: Ni-Mn-Ga合金磁熱效應(yīng)的優(yōu)化是制冷工程的研究熱點(diǎn)之一。為深入研究Ni-Mn-Ga合金的磁熱效應(yīng)，以Ni54+xMn19-xGa27 (x=0、0.4、1.0，摩爾分?jǐn)?shù))為研究對(duì)象，利用實(shí)驗(yàn)手段研究了合金的相變特性、組分及等靜壓對(duì)合金磁熱效應(yīng)的優(yōu)化與調(diào)控作用。結(jié)果表明：隨著Ni含量的增加，Ni54+xMn19–xGa27合金的馬氏體相變溫度逐漸升高，而居里溫度則先減小再增大；當(dāng)x=1.0時(shí)，合金出現(xiàn)了磁-結(jié)構(gòu)相變。相同外加磁場時(shí)，合金的最大磁熵變的絕對(duì)值(|ΔSM|max)及制冷量(WRC)隨Ni含量的增加而增大。當(dāng)磁場改變3 T時(shí)，合金x=1.0對(duì)應(yīng)的|ΔSM|max和WRC最大、約為8.2 J/(kg·K)和53.61 J/kg，分別是x為0、0.4的3.04、2.28倍與3.31、1.67倍。0.58 GPa等靜壓對(duì)合金x=1.0的|ΔSM|max影響可忽略不計(jì)，但等靜壓的應(yīng)用有利于拓寬合金的相變溫區(qū)、致使合金WRC提高了43.82%。為便于比較和工程應(yīng)用，給出了合金|ΔSM|max、WRC與外加磁場H的依賴關(guān)系。研究結(jié)果為Ni-Mn-Ga合金磁熱效應(yīng)的優(yōu)化、調(diào)控及工程應(yīng)用具有較好的指導(dǎo)意義。
關(guān)鍵字: Ni-Mn-Ga合金；磁制冷；馬氏體相變；磁熱效應(yīng)；等靜壓
（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
