近日，华中科技大学付英双团队研究了单层和双层NiI2原子尺度螺旋成像的自旋分辨成像。这一研究成果于2025年9月23日发表在《美国科学院院刊》杂志上。
单层范德华磁体的非共线磁序对于探索最小空间约束下的精细磁相互作用和推进小型化自旋电子器件至关重要。尽管它们意义重大，但实现原子尺度的识别仍颇具挑战性。
研究组利用自旋极化扫描隧道显微镜和密度泛函理论计算来确定在石墨烯覆盖的SiC（0001）衬底上生长的单层和双层NiI2中的自旋螺旋顺序。他们发现了两种不同的自旋螺旋态，Q向量与晶格方向对齐和偏离7°，分别表现出4.54和5.01倍晶格常数的周期性。这些发现与体积特性形成对比，并与他们的理论计算密切相关。令人惊讶的是，在有限大小的磁域中，自旋螺旋的非倍数会产生净磁矩，促进磁场下的集体自旋开关行为。他们的研究以原子尺度的分辨率揭示了单层极限下固有的非线性磁性，为探索自旋现象铺平了道路。
附：英文原文
Title: Spin-resolved imaging of atomic-scale helimagnetism in mono- and bilayer NiI2
Author: Miao, Mao-Peng, Liu, Nanshu, Zhang, Wen-Hao, Zhou, Jian-Wang, Wang, Dao-Bo, Wang, Cong, Ji, Wei, Fu, Ying-Shuang
Issue&Volume: 2025-9-23
Abstract: Noncollinear magnetic orders in monolayer van der Waals magnets are crucial for probing delicate magnetic interactions under minimal spatial constraints and advancing miniaturized spintronic devices. Despite their significance, achieving atomic-scale identification remains challenging. In this study, we utilized spin-polarized scanning tunneling microscopy and density functional theory calculations to identify spin-spiral orders in mono- and bilayer NiI2, grown on graphene-covered SiC(0001) substrates. We found two distinct spin-spiral states with Q vectors aligning and deviating by 7° from the lattice direction, exhibiting periodicities of 4.54 and 5.01 times the lattice constant, respectively. These findings contrast with bulk properties and align closely with our theoretical calculations. Surprisingly, the nonmultiples of spin spirals within finite-sized magnetic domains induce net magnetic moments, facilitating collective spin switching behavior under magnetic fields. Our research reveals intrinsic noncollinear magnetism at the monolayer limit with atomic-scale resolution, paving the way for exploring spin phenomena.
DOI: 10.1073/pnas.2422868122
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2422868122