中文摘要：

利用电弧炉制备了DyGa2和DyGa1.8Cu0.2合金样品。通过X射线粉末衍射方法和测量磁性研究了两种合金的晶体结构和磁性能。研究结果表明：DyGa2和DyGa1.8Cu0.2化合物的晶体结构为P6/mmm六方结构，用少量Cu替代Ga可使晶胞体积变小。DyGa2和DyGa1.8Cu0.2合金的奈尔温度分别为16 K和113 K，温度低于奈尔温度发生顺磁-反铁磁相变，且相变类型为二级相变。DyGa2在8 K温度附近发生变磁转变，为一级相变。DyGa2的最大磁熵变值为7.3 J/（kg ·K），具有较强的磁制冷能力，约为131 J/kg，在5 K附近出现－14.9 J/（kg？K）的异常负磁熵变，使DyGa2具有了温度自调节功能。掺杂少量Cu将合金的磁制冷温度提高到100 K附近，具有很好的磁制冷应用开发潜力。

英文摘要：

The crystal structures and magnetocaloric effect of DyGa2 and DyGa1.8Cu0.2 compounds were studied by X-ray powder diffraction and magnetic measurements. The main results show that the crystal structures of compounds are hexangular structure with space group of P6/mmm, and the cell volume decreases when Ga atoms are substituted by Cu atoms. The Neel temperatures of DyGa2 and DyGa1.8Cu0.2 are 16 and 113 K, respectively. They are anti-ferromagnetic below Neel temperature, which become paramagnetic near Neel temperature. The kind of this phase transiton is second order phase transition. The M vs. H curves for T≤ 8 K exhibit features that resemble those of a metamagnetic transformation which is first order phase transition. For a magnetic field change of 50 kOe, the maximum values of -ΔSM for DyGa2 is 7.3 J？kg-1？K-1, and cooling power is 131 J？kg-1. The values of -ΔSM for DyGa2 is unconventionally negative （-14.9 J？kg-1？K-1） at about 5 K. The phenomenon can be used in temperature control. A small amount of Cu doping makes the magnetic refrigeration temperatures to about 100 K. They are potential candidates for the practical magnetic refrigeration.