Abstract The structure, magnetic transition and magnetocaloric properties in the ternary gallium intermetallic compounds of Ho2Ni2Ga and Tm2Ni2Ga have been systematically investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and magnetization measurements. As found from powder XRD and Rietveld refinement, Ho2Ni2Ga and Tm2Ni2Ga crystallized in an orthorhombic structure of the W2B2Co type belonging to the Immm space group. Both compounds are ordering antiferromagnetically at low temperatures and under low magnetic fields together with a field-induced metamagnetic transition from antiferromagnetic (AFM) to ferromagnetic (FM). Peculiar and similar magnetocaloric properties are observed for both compounds, i. e., an inverse magnetocaloric effect (positive magnetic entropy change, ΔSM) under low magnetic field changes (ΔH) and at low temperatures together with a large normal reversible magnetocaloric effect under high ΔH. The positive ΔSM below/at the Neel temperatures (TN) is ascribed to first order transition from antiferromagnetic (AFM) to ferromagnetic (FM) states, whereas the negative ΔSM above TN is due to the fact of the magnetic transition from paramagnetic (PM) to ferromagnetic (FM) states. Based on the field-dependent magnetization data, the maximum magnetic entropy change (−ΔSMmax), relative cooling power (RCP) and refrigerant capacity (RC) are established, and the corresponding values are 9.6 J/kg K, 276 J/kg and 206 J/kg for Ho2Ni2Ga, and are 4.3 J/kg K, 60 J/kg and 46 J/kg for Tm2Ni2Ga, respectively, for a magnetic field change of 0–70 kOe.

中文翻译：

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反铁磁性 Ho 2 Ni 2 Ga 和 Tm 2 Ni 2 Ga 化合物的变磁跃迁和磁热特性

摘要 采用 X 射线衍射 (XRD)、扫描电子显微镜 (SEM)、能谱仪 (EDS) 和磁化测量方法系统地研究了 Ho2Ni2Ga 和 Tm2Ni2Ga 三元镓金属间化合物的结构、磁跃迁和磁热性能。根据粉末 XRD 和 Rietveld 精修发现，Ho2Ni2Ga 和 Tm2Ni2Ga 以属于 Immm 空间群的 W2B2Co 型正交结构结晶。这两种化合物在低温和低磁场下都呈反铁磁性有序排列，同时场诱导的从反铁磁性 (AFM) 到铁磁性 (FM) 的变磁转变。两种化合物都观察到了独特且相似的磁热特性，即逆磁热效应（正磁熵变，ΔSM) 在低磁场变化 (ΔH) 和低温下以及高 ΔH 下的大的正常可逆磁热效应。低于/在尼尔温度 (TN) 处的正 ΔSM 归因于从反铁磁 (AFM) 到铁磁 (FM) 状态的一阶跃迁，而高于 TN 的负 ΔSM 归因于从顺磁 (PM) 的磁跃迁到铁磁 (FM) 状态。根据场相关磁化数据，建立了最大磁熵变（-ΔSMmax）、相对冷却功率（RCP）和制冷剂容量（RC），对应的值为 9.6 J/kg K、276 J/kg 和对于 0–70 kOe 的磁场变化，Ho2Ni2Ga 为 206 J/kg，Tm2Ni2Ga 分别为 4.3 J/kg K、60 J/kg 和 46 J/kg。