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.

本征磁性原子在层状二维（2D，two-dimensional）材料的范德瓦尔斯（van der Waals, vdW）间隙内发生自插层，为低维体系的磁学调控提供了新的自由度。在各类范德瓦尔斯磁体中，碲化钒体系因可灵活调控非化学计量比组分，成为探究磁性杂质层间有序-无序转变的极具价值的研究对象。本研究结合高分辨扫描透射电子显微镜（STEM，scanning transmission electron microscopy）分析、密度泛函理论（DFT，density functional theory）计算与磁学表征手段，揭示了化学气相沉积（CVD，chemical vapor deposition）法制备的内嵌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。钒插层的偏析作用可局域稳定自插层V₃Te₄磁相，该相具有畸变类1T′单斜晶体结构。该相转变由插层钒离子引入的电子掺杂所调控。磁滞回线结果显示，该纳米片表现出超顺磁性；而变温磁化曲线则证实，低温下纳米团簇呈现集体超自旋玻璃磁行为。借助四维（4D，four-dimensional）STEM衍射成像技术，我们观测到电子显微镜内强磁场环境下样品中形成了集体弥散磁畴结构。本研究结果可为二维极限下的稀磁学研究，以及面向自旋电子学应用的磁学调控策略提供重要参考。