Collective Magnetic Behavior in Vanadium Telluride Induced by Self-Intercalation

Self-intercalation of native magnetic atoms within the van der Waals (vdW) gap of layered two-dimensional (2D) materials provides a degree of freedom to manipulate magnetism in low-dimensional systems. Among various vdW magnets, the vanadium telluride is an interesting system to explore the interlayer order–disorder transition of magnetic impurities due to its flexibility in taking nonstoichiometric compositions. In this work, we combine high-resolution scanning transmission electron microscopy (STEM) analysis with density functional theory (DFT) calculations and magnetometry measurements, to unveil the local atomic structure and magnetic behavior of V-rich V1+xTe2 nanoplates with embedded V3Te4 nanoclusters grown by chemical vapor deposition (CVD). The segregation of V intercalations locally stabilizes the self-intercalated V3Te4 magnetic phase, which possesses a distorted 1T′-like monoclinic structure. This phase transition is controlled by the electron doping from the intercalant V ions. The magnetic hysteresis loops show that the nanoplates exhibit superparamagnetism, while the temperature-dependent magnetization curves evidence a collective superspin-glass magnetic behavior of the nanoclusters at low temperature. Using four-dimensional (4D) STEM diffraction imaging, we reveal the formation of collective diffuse magnetic domain structures within the sample under the high magnetic fields inside the electron microscope. Our results shed light on the studies of dilute magnetism at the 2D limit and on strategies for the manipulation of magnetism for spintronic applications.层状二维（2D，two-dimensional）材料的范德瓦尔斯（van der Waals, vdW）间隙中，本征磁性原子的自插层为低维体系的磁学调控提供了全新的自由度。在各类范德瓦尔斯磁体中，碲化钒（vanadium telluride）是探究磁性杂质层间有序-无序转变的极具研究价值的体系，因其可灵活适配非化学计量配比。本研究将高分辨扫描透射电子显微镜（scanning transmission electron microscopy, STEM）分析、密度泛函理论（density functional theory, DFT）计算与磁学测量相结合，揭示了通过化学气相沉积（chemical vapor deposition, CVD）制备的、内嵌V₃Te₄纳米团簇的富钒V₁₊ₓTe₂纳米片的局域原子结构与磁学行为。钒插层的偏析可局部稳定自插层的V₃Te₄磁性相，该相具有畸变的类1T'单斜晶体结构，其相变过程由插层钒离子引入的电子掺杂调控。磁滞回线（magnetic hysteresis loops）测试表明，该纳米片表现出超顺磁性（superparamagnetism）；而温度依赖磁化曲线（temperature-dependent magnetization curves）则证实，纳米团簇在低温下呈现集体超自旋玻璃磁行为（collective superspin-glass magnetic behavior）。借助四维（4D，four-dimensional）扫描透射电子显微镜衍射成像技术，我们观测到在电镜内部强磁场环境下，样品中形成了集体弥散磁畴结构（collective diffuse magnetic domain structures）。本研究结果为二维极限下的稀磁学研究以及自旋电子学（spintronics）应用中的磁调控策略提供了重要的理论与实验参考。