发表机构
University of Oxford; Harvard John A. Paulson School of Engineering and Applied Sciences; Florida State University; Max-Planck-Institut fur Festkörperforschung（牛津大学; 哈佛大学约翰·A·保尔森工程与应用科学学院; 佛罗里达州立大学; 马克斯·普朗克固体研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过高场磁转矩测量和理论计算，揭示了三角超固态 $2H$-AgNiO$_2$ 中相变感生的角向调制，并构建了极坐标相图，证实了自旋超固态序的角度依赖表现。
AI 中文摘要
易轴阻挫三角晶格反铁磁体为稳定多种奇异磁相提供了重要平台。三角层状氧化物 $2H$-AgNiO$_2$ 是一个独特的模型体系，其中包含由巡游电子蜂窝晶格包围的局域（$S=1$）矩晶格。在 $T_{\ m N}=19$ K 以下，体系呈现共线条纹反铁磁序，而外加磁场则诱导出一系列相变，据推测其中包含磁超固态相。在本研究中，我们对单晶样品在高达 45 T 的静磁场下进行了详细的角分辨和磁场依赖的转矩测量。转矩的角依赖在第一超固态相附近呈现锯齿形信号，而在接近 $T_{\ m N}$ 时，出现了意外的额外调制。另一方面，转矩的场依赖表明存在四个场致异常，它们随场方向的变化以不同方式演化。为理解这些复杂行为并评估局域矩的作用，我们采用最小自旋模型进行了平均场和蒙特卡洛计算，并在不同温度下构建了全面的极坐标相图。我们发现，转矩的角依赖可以通过场旋转穿越不同相边界来理解，并识别出实验与理论极坐标相图之间的定性相似性。我们的研究凸显了 $2H$-AgNiO$_2$ 作为一个丰富的各向异性体系，为自旋超固态序如何在角度依赖的磁转矩中显现提供了有力的范例。
英文摘要
Easy-axis frustrated triangular lattice antiferromagnets provide an important playground for stabilising a wide range of exotic magnetic phases. The delafossite $2H$-AgNiO$_2$ offers a unique model system containing a lattice of localised ($S=1$) moments surrounded by a honeycomb of itinerant electrons. Below $T_{\rm N} =19$ K, the system exhibits collinear stripe antiferromagnetic order, whereas applied magnetic fields induce a cascade of transitions which has been proposed to contain a magnetic supersolid phase. In this study, we perform detailed angular and field-dependent torque measurements in static fields of up to 45~T on single crystal samples. The angular dependence of the torque displays a sawtooth-shaped signal close to the first supersolid phase, while near $T_{\rm N}$, an unexpected additional modulation emerges. On the other hand, the field dependence of the torque indicates the presence of four field-induced anomalies which evolve in distinct ways as a function of field orientation. To understand these complex behaviours and assess the role of local moments, we employ mean-field and Monte-Carlo calculations on a minimal spin model and construct comprehensive polar phase diagrams at different temperatures. We find that the angular dependence of the torque can be understood in terms of crossing different phase boundaries by field rotation, and we identify qualitative similarities between the experimental and theoretical polar phase diagrams. Our study highlights $2H$-AgNiO$_2$ as a rich anisotropic system that provides a robust example of how spin supersolid orders can manifest in angle-dependent magnetic torque.
Comments11 pages, 6 figures
