多铁材料NiI₂中自旋螺旋态的维度交叉与局域应变诱导偏转
Dimensional crossover and local strain induced deflection of the spin spiral state in multiferroic NiI2
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中文总结 AI 辅助
本研究结合实验与理论方法，揭示了多铁材料NiI₂中自旋螺旋态随厚度变化的维度交叉规律，发现局域应变可调控自旋螺旋，确立了两种非共线螺旋磁性的调控手段。
中文摘要 AI 辅助
低维多铁材料在集成磁电器件领域具有巨大应用前景。自旋螺旋态近期被发现可在单层范德华（vdW）材料NiI₂中诱导铁电性，但该态向二维极限的演化及调控机制仍不明确。本研究结合自旋极化扫描隧道显微镜、逐层薄膜生长技术与多尺度理论建模，探究NiI₂薄膜中的自旋螺旋：当薄膜厚度从1个单层增至7个单层时，自旋螺旋波长持续增加，波矢从近[110]方向旋转至[1-10]方向，证明维度交叉主要由层间交换能增强驱动；此外，薄膜褶皱可导致自旋螺旋波矢偏转，该现象源于局域曲率对交换相互作用的调控。本研究确立了厚度与局域应变作为范德华多铁材料中非共线螺旋磁性及伴随电极化的两种调控手段，为相关器件设计提供了关键依据。
英文摘要
Low-dimensional multiferroics hold great promise for integrated magnetoelectric devices. Spin spiral state has recently been shown to induce ferroelectricity in single-layer van der Waals (vdW) material NiI2. However, how this state evolves and can be tuned towards the two-dimensional limit remain unclear. Here, we combine spin-polarized scanning tunneling microscopy, layer-by-layer film growth, and multi-scale theoretical modeling to investigate the spin spirals in NiI2 thin films. As the film thickness increases from 1 to 7 monolayers, we observed a continuous increase of spin-spiral wavelength and a rotation of wavevector from near [110] to [1-10] direction, which evidences a dimensional crossover primarily driven by enhanced interlayer exchange energy. Moreover, we find that the film wrinkles can cause deflection of the spin spiral wavevector, which is caused by local curvature induced modification of exchange interactions. Our findings establish thickness and local strain as two tuning methods for engineering non-collinear helical magnetism and accompanied electric polarization in vdW multiferroics.
