School of Materials Science and Engineering, Peking University, Beijing100871, China.
Department of Physics, National University of Singapore, 2 Science Drive 3, 117551Singapore.
J Am Chem Soc. 2023 Feb 15;145(6):3624-3635. doi: 10.1021/jacs.2c12801. Epub 2023 Feb 3.
Transition-metal trihalides MX (M = Cr, Ru; X = Cl, Br, and I) belong to a family of novel two-dimensional (2D) magnets that can exhibit topological magnons and electromagnetic properties, thus affording great promises in next-generation spintronic devices. Rich magnetic ground states observed in the MX family are believed to be strongly correlated to the signature Kagome lattice and interlayer van der Waals coupling raised from distinct stacking orders. However, the intrinsic air instability of MX makes their direct atomic-scale analysis challenging. Therefore, information on the stacking-registry-dependent magnetism for MX remains elusive, which greatly hinders the engineering of desired phases. Here, we report a nondestructive transfer method and successfully realize an intact transfer of bilayer MX, as evidenced by scanning transmission electron microscopy (STEM). After surveying hundreds of MX thin flakes, we provide a full spectrum of stacking orders in MX with atomic precision and calculated their associated magnetic ground states, unveiled by combined STEM and density functional theory (DFT). In addition to well-documented phases, we discover a new monoclinic 2/ phase in the antiferromagnetic (AFM) structure widely existing in MX. Rich stacking polytypes, including 2/, 2/, 3̅, 312, , provide rich and distinct magnetic ground states in MX. Besides, a high density of strain soliton boundaries is consistently found in all MX, combined with likely inverted structures, allowing AFM to ferromagnetic (FM) transitions in most MX. Therefore, our study sheds light on the structural basis of diverse magnetic orders in MX, paving the way for modulating magnetic couplings stacking engineering.
过渡金属三卤化物 MX（M = Cr、Ru；X = Cl、Br 和 I）属于一类新型二维（2D）磁体，它们可以表现出拓扑磁子和电磁特性，因此在下一代自旋电子器件中具有很大的应用前景。在 MX 家族中观察到的丰富磁基态被认为与独特的 kagome 晶格和由不同堆积顺序引起的层间范德华耦合密切相关。然而，MX 的内在空气不稳定性使得直接进行原子级分析具有挑战性。因此，关于 MX 的堆积顺序依赖性磁体的信息仍然难以捉摸，这极大地阻碍了所需相的工程设计。在这里，我们报告了一种非破坏性的转移方法，并成功地实现了双层 MX 的完整转移，这可以通过扫描透射电子显微镜（STEM）来证明。在对数百个 MX 薄片进行调查后，我们以原子精度提供了 MX 中完整的堆积顺序谱，并通过结合 STEM 和密度泛函理论（DFT）计算了它们相关的磁基态。除了记录良好的相之外，我们还在 MX 中广泛存在的反铁磁（AFM）结构中发现了一种新的单斜 2/相。丰富的堆积多型，包括 2/、2/、3̅、312、、，在 MX 中提供了丰富而独特的磁基态。此外，在所有 MX 中都一致发现了高密度的应变孤子边界，再加上可能的倒置结构，允许 AFM 在大多数 MX 中发生到 FM 的转变。因此，我们的研究揭示了 MX 中多种磁序的结构基础，为通过堆积工程调节磁耦合铺平了道路。
