中国科学院赣江创新研究院莫兆军团队报道了多晶EuB₄O₇化合物的巨低场低温磁热效应。相关研究成果发表在2024年1月23日出版的国际学术期刊《美国化学会杂志》。

为了解决氦-3资源短缺和价格昂贵的问题，绝热消磁制冷技术作为氦-3制冷技术的替代品受到了广泛关注。

该文研究了EuB₄O₇化合物的磁性和超低温磁热效应。磁性和准绝热消磁测量的结果表明，EuB₄O₇不存在高于0.4K的磁序。最近相邻的Eu原子之间的偶极相互作用具有约800mK的特征能量，这可能引起大的MCE。μ₀H=0–10 kOe、0–20 kOe和0–50 kOe时，最大磁熵变化分别达到22.8、36.2和47.6 J·kg^–1 K^–1。

准绝热消磁装置的测量表明，多晶EuB₄O₇可达到的最低温度（289mK）低于商用制冷剂Gd₃Ga₅O₁₂（GGG）单晶的最低温度。在700mK以下，在2K的环境温度下，保持时间超过70分钟，证明了EuB₄O₇具有优异的冷却性能。

附：英文原文

Title: Giant Low-Field Cryogenic Magnetocaloric Effect in a Polycrystalline EuB4O7 Compound

Author: Yuanpeng Wang, Junsen Xiang, Lei Zhang, Jianjian Gong, Wei Li, Zhaojun Mo, Jun Shen

Issue&Volume: January 23, 2024

Abstract: To deal with the shortage and high price of helium-3 resources, adiabatic demagnetization refrigeration technology as an alternative to helium-3-based refrigeration technology has received much attention. The magnetism and ultralow-temperature magnetocaloric effect (MCE) of the EuB4O7 compound have been investigated. The results of magnetic and quasi-adiabatic demagnetization measurements suggest the absence of a magnetic order above 0.4 K for EuB4O7. The dipolar interaction between the nearest-neighbor Eu atoms has a characteristic energy of about 800 mK, which may induce a large MCE. The maximum magnetic entropy change reaches 22.8, 36.2, and 47.6 J·kg–1 K–1 at μ0H = 0–10 kOe, 0–20 kOe, and 0–50 kOe, respectively. Measurements by a quasi-adiabatic demagnetization device show that the lowest temperature achievable (289 mK) for polycrystalline EuB4O7 is lower than that (362 mK) for the commercial refrigerant Gd3Ga5O12 (GGG) single crystals. The hold time is more than 70 min below 700 mK, with an environment temperature of 2 K, proving that EuB4O7 exhibits superior cooling performance.

DOI: 10.1021/jacs.3c12158

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.3c12158