Low-temperature magnetocaloric materials are of great importance for potential applications of gas liquefaction such as nitrogen, hydrogen and helium for their low liquidation temperatures (∼4 K for helium, ∼20 K for hydrogen and ∼77 K for nitrogen respectively), of which the working temperature, the maximal magnetic entropy change ((-ΔSM)max), the maximal adiabatic temperature change ((ΔTad)max), and the temperature average entropy change (TEC) are the key assessment parameters. Herein, we designed and synthesized Er1-xTmxGa series compounds based on the optimization of the spin quantum number (Spin) with their magnetic ordering temperature successfully adjusted from 31.0 K to 15.0 K, which covers the liquid hydrogen temperature range. Particularly, Er0.8Tm0.2Ga shows outstanding (-ΔSM)max, TEC(20), and (ΔTad)max values of 13.6 J/kg K, 10.1 J/kg K, and 4.3 K under the field change of 0–2 T, respectively, which are increased by 32.0 %, 36.4 %, and 48.2 % compared with the parent ErGa compound. It should be noted that the refrigerant capacity (RC) of Er0.8Tm0.2Ga is not only larger than ErGa but also larger than TmGa. Furthermore, neutron powder diffraction (NPD) was employed on Er0.8Tm0.2Ga to reveal the physical mechanism of its enhanced magnetocaloric effect (MCE). It is found that for Er0.8Tm0.2Ga the more pronounced order-to-disorder transition than the spin reorientation (SR) transition, the characteristic second order phase transition, and the existence of the short-range magnetic ordering above the magnetic ordering temperature should be jointly responsible for its large magnetocaloric effect.

中文翻译：

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Er1-xTmxGa 材料中接近液氢温度的大磁热效应


低温磁热材料对于气体液化的潜在应用非常重要，例如氮气、氢气和氦气，因为它们的液化温度较低（氦气为 ∼4 K，氢气为 ∼20 K，氮气为 ∼77 K），其中工作温度、最大磁熵变化 （（-ΔSM）max）、最大绝热温度变化 （（ΔTad）max）、 和温度平均熵变 （TEC） 是关键的评估参数。在此，我们基于自旋量子数 （Spin） 的优化设计合成了 Er1-xTmxGa 系列化合物，其磁排序温度成功从 31.0 K 调节到 15.0 K，覆盖了液氢温度范围。特别是，Er0.8Tm0.2Ga 在 0–2 T 的磁场变化下表现出优异的 （-ΔSM）max、TEC（20） 和 （ΔTad）max 值分别为 13.6 J/kg K、10.1 J/kg K 和 4.3 K，与母体 ErGa 化合物相比增加了 32.0 %、36.4 % 和 48.2 %。需要注意的是，Er0.8Tm0.2Ga的制冷剂容量（RC）不仅大于ErGa，而且也大于TmGa。此外，对 Er0.8Tm0.2Ga 采用中子粉衍射 （NPD） 来揭示其增强磁热效应 （MCE） 的物理机制。研究发现，对于 Er0.8Tm0.2Ga，比自旋重新取向 （SR） 转变更明显的有序到无序转变、特征二阶相变以及磁有序温度以上短程磁有序的存在应该是其较大的磁热效应的共同原因。