Kagome networks of ferromagnetically or antiferromagnetically coupled magnetic moments represent important models in the pursuit of a diverse array of novel quantum and topological states of matter. Here, we explore a family of Cu²⁺-containing metal–organic frameworks (MOFs) bearing kagome layers pillared by ditopic organic linkers with the general formula Cu₃(CO₃)₂(x)₃·2ClO₄ (MOF-x), where x is 1,2-bis(4-pyridyl)ethane (bpe), 1,2-bis(4-pyridyl)ethylene (bpy), or 4,4′-azopyridine (azpy). Despite more than a decade of investigation, the nature of the magnetic exchange interactions in these materials remained unclear, meaning that whether the underlying magnetic model is that of an kagome ferromagnet or antiferromagnet is unknown. Using single-crystal X-ray diffraction, we have developed a chemically intuitive crystal structure for this family of materials. Then, through a combination of magnetic susceptibility, powder neutron diffraction, and muon-spin spectroscopy measurements, we show that the magnetic ground state of this family consists of ferromagnetic kagome layers that are coupled antiferromagnetically via their extended organic pillaring linkers.

中文翻译：

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在一系列金属-有机框架中发现 Kagome 铁磁体

铁磁或反铁磁耦合磁矩的 Kagome 网络代表了追求各种新的量子和拓扑物质状态的重要模型。在这里，我们探索了一系列含 Cu ²⁺的金属有机框架 (MOF) ，它们带有由具有通式 Cu ₃ (CO ₃ ) ₂ ( x ) ₃ ·2ClO ₄ (MOF- x )的双体有机连接体支撑的 kagome 层, 其中x是 1,2-双(4-吡啶基)乙烷 ( bpe )、1,2-双(4-吡啶基)乙烯 ( bpy ) 或 4,4'-偶氮吡啶 ( azpy）。尽管进行了十多年的研究，但这些材料中磁性交换相互作用的性质仍不清楚，这意味着潜在的磁性模型是kagome铁磁体还是反铁磁体尚不清楚。使用单晶 X 射线衍射，我们为这一系列材料开发了一种化学上直观的晶体结构。然后，通过磁化率、粉末中子衍射和 μ 子自旋光谱测量的组合，我们表明该家族的磁性基态由铁磁 kagome 层组成，这些层通过其扩展的有机支柱连接体反铁磁耦合。