AI 中文总结
研究三角晶格 NdMgAl$_{11}$O$_{19}$ 的磁基态和磁热效应，通过磁化率、比热测量及准绝热退磁测量等方法，发现其在低场有优异制冷性能，为下一代低温磁制冷剂提供设计原则。
AI 中文摘要
在低于开尔文温度的磁制冷中，需要制冷材料通过抑制磁有序来在低温下保持大的磁熵。量子自旋液体（QSL）在避免长程磁有序的同时，在最低温度下保持强量子涨落，因此为实现高性能磁制冷剂提供了一个有前景的平台。本文研究了六铝酸盐 NdMgAl$_{11}$O$_{19}$ 的磁基态和磁热效应，其中 Nd$^{3+}$ 离子形成三角晶格网络。磁化率和比热测量表明在低至 50 mK 时存在磁动态状态，与 QSL 态一致。比热测量进一步揭示在 50 mK 以下保留了大量磁熵。准绝热退磁测量表明 NdMgAl$_{11}$O$_{19}$ 具有优异的冷却性能，仅 2 T 的小磁场变化就能使其从 1.9 K 冷却到 113 mK。这种出色的制冷性能归因于与类 QSL 基态相关的持续自旋涨落、大的有效 g 因子以及易轴方向交换相互作用的小尺寸。本研究表明，稀土磁体中的挫折与强自旋 - 轨道耦合和晶体电场效应相结合，为下一代低温磁制冷剂提供了一种有前景的设计原则。
英文摘要
Magnetic refrigeration in the sub-Kelvin regime requires refrigerant materials to retain a large magnetic entropy at low temperatures by suppressing magnetic ordering. Quantum spin liquids (QSLs), which evade long-range magnetic ordering while retaining strong quantum fluctuations to the lowest temperatures, therefore provide a promising platform for realizing high-performance magnetic refrigerants. Here, we investigate the magnetic ground state and the magnetocaloric effect of the hexaaluminate, NdMgAl$_{11}$O$_{19}$, in which the Nd$^{3+}$ ions form a network of triangular lattices. Magnetic susceptibility and specific heat measurements indicate a magnetically dynamic state down to 50~mK, consistent with a QSL state. Specific heat measurements further reveal substantial magnetic entropy retained below 50~mK. Quasi-adiabatic demagnetization measurements demonstrate a superior cooling performance of NdMgAl$_{11}$O$_{19}$, which can be cooled to 113~mK from 1.9~K by only a small magnetic field change of 2~T. The outstanding refrigeration performance is attributed to the persistent spin fluctuations associated with the QSL-like ground state, together with a large effective \textit{g} factor and the smallness of the exchange interactions along the easy-axis direction. This study demonstrates that frustration, combined with strong spin-orbit coupling and crystal-electric-field effect in the rare earth magnets provides a promising design principle for next-generation cryogenic magnetic refrigerants.
Comments8 pages, 4 figures, 1 table
