发表机构
Indian Association for the Cultivation of Science; Deutsches Elektronen–Synchrotron DESY; Christian-Albrechts-Universität zu Kiel（印度科学文化研究所; 德国电子同步辐射中心; 基尔大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
首次合成无水立方Na$_2$IrCl$_6$单晶，其具有fcc反铁磁基态（转变温度1.91 K），填补了完美立方空位有序家族缺失成员，为研究强Kitaev相互作用和$J_{eff}$ = $\ rac{1}{2}$基态提供了新平台。
AI 中文摘要
空位有序双钙钛矿（VODPs）已被知晓超过100年，但至今其精确晶体结构和磁性基态仍存在争议。具有面心立方（fcc）反铁磁基态的无水VODP铱酸盐（$A_2$Ir$X_6$；$A$ = K$^+$、(NH$_4$)$^+$、Cs$^+$、Rb$^+$，$X$ = F$^-$、Cl$^-$、Br$^-$）提供了一个化学定义明确的平台，用于研究局域库仑排斥、晶体场、自旋轨道耦合以及竞争的Heisenberg和Kitaev相互作用的影响。有趣的是，其中基于Na的VODP铱酸盐似乎具有不寻常的依赖水合作用的结构和磁性不确定性。因此，具有fcc反铁磁性的立方Na$_2$IrCl$_6$体系一直无法稳定获得。在此，我们首次报道了具有fcc结构、反铁磁转变温度为1.91 K的无水Na$_2$IrCl$_6$单晶的合成和全面表征。热重分析证实了不存在晶格水，并展示了晶体在高达453 K的热稳定性。这里报道的立方相与先前描述的“无水”单斜Na$_2$IrCl$_6$形成对比，突出了Na基VODP铱酸盐中结构与物理性质之间的强关联。这种新材料为探索另一个潜在的完美$J_{eff}$ = $\ rac{1}{2}$八面体以及最近邻（nn）Ir离子对中随之而来的强Kitaev相互作用提供了令人兴奋的平台。
英文摘要
Vacancy ordered double perovskites (VODPs) have been known for more than 100 years, but their exact crystal structures and magnetic ground state remained controversial till date. Anhydrous VODP iridates ($A_2$Ir$X_6$; $A$ = K$^+$, (NH$_4$)$^+$, Cs$^+$, Rb$^+$, and $X$ = F$^-$, Cl$^-$, Br$^-$), having $face-centered~cubic$ (fcc) antiferromagnetic ground state, offer a chemically well-defined platform to investigate the influence of on-site Coulomb repulsion, crystal field, spin-orbit coupling, and competing Heisenberg and Kitaev interactions. Interestingly, among these, the Na-based VODP iridates seem to possess an unusual hydration dependent structural and magnetic uncertainty. As a result, a cubic Na$_2$IrCl$_6$ system having fcc antiferromagnetism could not be stabilized ever. Here, for the first time, we report the synthesis and comprehensive characterization of anhydrous Na$_2$IrCl$_6$ single crystals having fcc structure with antiferromagnetic transition temperature of 1.91 K. Thermogravimetric analysis establishes the absence of lattice water and also demonstrates thermal stability of the crystals up to 453 K. The cubic phase reported here contrasts with previously described 'anhydrous' monoclinic Na$_2$IrCl$_6$ and highlights the strong structural and physical property relationship in Na-based VODP iridates. This new material offers an exciting playing ground for exploring another potential perfect $J_{eff}$ = $\frac{1}{2}$ octahedra and the consequent strong Kitaev interaction within the nearest-neighbor (nn) pairs of Ir ions.
