AI 中文总结
该研究针对面心立方结构的稀土双钙钛矿Ba₂YbNbO₆和Ba₂NdNbO₆，证实其存在自旋轨道耦合诱导的j_eff=1/2基态与中等阻挫的长程磁有序，为稀土自旋轨道纠缠磁体提供了新候选体系。
AI 中文摘要
寻找Kitaev材料候选物的研究主要集中在具有不同晶格几何结构的4d和5d过渡金属化合物上，相比之下，对稀土4f体系的研究迄今主要局限于蜂窝和三角晶格。本研究探讨稀土基双钙钛矿Ba₂YbNbO₆和Ba₂NdNbO₆，二者结晶为面心立方结构。磁化率和热容测量证实，强自旋轨道耦合（SOC）与晶体电场效应产生孤立的j_eff=1/2克莱默双重态基态，密度泛函理论计算进一步支持这一结论。毫开尔文温度下的热力学测量显示，两种化合物均存在具有中等阻挫的长程磁有序，这种磁有序的出现可通过有序-无序机制解释，该机制是针对具有有限Kitaev相互作用的稀土面心立方晶格从理论上提出的。研究结果表明Ba₂YbNbO₆和Ba₂NdNbO₆是颇具潜力的稀土自旋轨道纠缠磁体，并推动进一步实验与理论研究以确定完整的交换张量，阐明潜在磁相互作用的微观起源。
英文摘要
The search for candidate Kitaev materials has largely focused on 4$d$ and 5$d$ transition-metal compounds with various lattice geometries. In contrast, investigations of rare-earth 4$f$ systems have thus far been restricted mainly to honeycomb and triangular lattices. In this work, we investigate the rare-earth-based double perovskites Ba$_2$YbNbO$_6$ and Ba$_2$NdNbO$_6$, which crystallize in a face-centered cubic structure. Magnetization and heat-capacity measurements establish isolated ${j_{\rm eff}} = 1/2$ Kramers doublet ground states arising from strong spin-orbit coupling (SOC) and crystal electric-field effects, which are further supported by density-functional theory calculations. Millikelvin-temperature thermodynamic measurements reveal long-range magnetic order with moderate frustration in both compounds. The emergence of magnetic order may be understood within an order-by-disorder scenario, as theoretically proposed for rare-earth fcc lattices with finite Kitaev interactions. Our results thus identify Ba$_2$YbNbO$_6$ and Ba$_2$NdNbO$_6$ as promising rare-earth spin-orbit-entangled magnets and motivate further experimental and theoretical investigations aimed at determining the complete exchange tensor to elucidate the microscopic origin of the underlying magnetic interactions.
Comments13 pages and six figures
Journal refPhyscal Review B 114, 144403 (2016)
