范德华氧卤化物DyOCl、DyOBr和DyOI中可调控的 bilayer 间磁关联及候选多极物理
Tunable inter-bilayer magnetic correlations and candidate multipolar physics in the van der Waals oxyhalides DyOCl, DyOBr, and DyOI
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中文总结 AI 辅助
该研究对比分析DyOX系列范德华磁体的磁特性，明确其可调控bilayer间磁关联，揭示相关多极物理候选方向，为低维稀土磁体研究提供新体系。
中文摘要 AI 辅助
稀土范德华磁体为在块体晶体中结合强自旋轨道耦合、大磁矩和低维度提供了途径。我们报道了对镝氧卤化物DyOX（X=Cl、Br、I）的对比研究，该系列化合物实现了由可调控范德华间隙分隔的Dy³⁺磁矩的平方 bilayer 网络。结构精修表明，卤离子半径增大时， bilayer 间距显著膨胀，而局部 bilayer 几何几乎不变。磁化和热容测量显示，三种化合物均存在两个低温异常：奈尔温度TN~7-10 K处的反铁磁有序，以及TQ~27-30 K处的较宽异常。对DyOCl和DyOBr的单晶磁化测量确立了强的c轴硬各向异性，这与DyOCl的晶体场分析结果一致，该分析给出类XY基态g张量。中子衍射显示DyOCl中存在长程反铁磁有序，而DyOBr和DyOI则表现出尖锐的磁散射与沃伦型弥散特征共存，这与面内强关联及 bilayer 间晶格匹配不完善一致。对DyOCl的非弹性中子散射在25-30 meV附近识别出晶体场激发，以及在10 meV附近的额外磁模式，其温度依赖性与高温异常相关。综上，这些结果确立DyOX为可调控的准二维稀土磁体系，并指向与低能晶体场态相关的候选多极物理。确定TQ处的序参量需要直接探测四极有序，如共振X射线散射或弹性常数测量。
英文摘要
Rare-earth van der Waals magnets provide a route to combining strong spin-orbit coupling, large magnetic moments, and reduced dimensionality in bulk crystals. We report a comparative study of the dysprosium oxyhalides DyOX (X = Cl, Br, I), which realize square-bilayer networks of Dy3+ moments separated by a tunable van der Waals gap. Structural refinements show that increasing the halide ionic radius strongly expands the inter-bilayer spacing while leaving the local bilayer geometry nearly unchanged. Magnetization and heat-capacity measurements reveal two low-temperature anomalies in all three compounds: antiferromagnetic order at TN ~ 7-10 K and a broader anomaly near TQ ~ 27-30 K. Single-crystal magnetization on DyOCl and DyOBr establishes a strong hard-c-axis anisotropy, consistent with crystal-field analysis of DyOCl, which yields an XY-like ground-state g tensor. Neutron diffraction shows long-range antiferromagnetic order in DyOCl, whereas DyOBr and DyOI exhibit sharp magnetic scattering coexisting with Warren-like diffuse features, consistent with robust in-plane correlations and imperfect inter-bilayer registry. Inelastic neutron scattering on DyOCl identifies crystal-field excitations near 25-30 meV and an additional magnetic mode near 10 meV whose temperature dependence is tied to the high-temperature anomaly. Taken together, these results establish DyOX as a tunable family of quasi-two-dimensional rare-earth magnets and point to candidate multipolar physics associated with low-lying crystal-field states. Direct probes of quadrupolar order, such as resonant x-ray scattering or elastic-constant measurements, will be required to determine the order parameter at TQ.
