The van der Waals compound, ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, is the first intrinsic magnetic topological insulator, providing a materials platform for exploring exotic quantum phenomena such as the axion insulator state and the quantum anomalous Hall effect. However, intrinsic structural imperfections lead to bulk conductivity, and the roles of magnetic defects are still unknown. With higher concentrations of the same types of magnetic defects, the isostructural compound ${\mathrm{MnSb}}_2{\mathrm{Te}}_4$ is a better model system for a systematic investigation of the connections among magnetism, topology, and lattice defects. In this work, the impact of antisite defects on the magnetism and electronic structure is studied in ${\mathrm{MnSb}}_2{\mathrm{Te}}_4$. Mn-Sb site mixing leads to complex magnetic structures and tunes the interlayer magnetic coupling between antiferromagnetic and ferromagnetic. The detailed nonstoichiometry and site mixing of ${\mathrm{MnSb}}_2{\mathrm{Te}}_4$ crystals depend on the growth parameters, which can lead to $\approx 40\%$ of Mn sites occupied by Sb and $\approx 15\%$ of Sb sites by Mn in as-grown crystals. Single-crystal neutron diffraction and electron microscopy studies show nearly random distribution of the antisite defects. Band structure calculations suggest that the Mn-Sb site mixing favors a ferromagnetic interlayer coupling, consistent with experimental observation, but is detrimental to the band inversion required for a nontrivial topology. Our results suggest a long-range magnetic order of Mn ions sitting on Bi sites in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$. The effects of site mixing should be considered in all layered heterostructures that consist of alternating magnetic and topological layers, including the entire family of $\mathrm{MnTe}({\mathrm{Bi}}_2{\mathrm{Te}}_3{)}_n$, its Sb analogs, and their solid solution.

中文翻译：

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工程电磁拓扑绝缘子的现场混合

范德华斯大院， ${\mathrm{锰铋}}_{\mathrm{2个}}{特}_4$，是第一个本征磁性拓扑绝缘体，为探索奇特的量子现象（例如轴突绝缘子状态和量子异常霍尔效应）提供了一个材料平台。但是，固有的结构缺陷会导致整体导电性，并且磁性缺陷的作用仍是未知的。当具有更高浓度的相同类型的磁缺陷时，同构化合物${\mathrm{锰锑}}_{\mathrm{2个}}{特}_4$是一个更好的模型系统，用于系统研究磁性，拓扑和晶格缺陷之间的联系。在这项工作中，研究了反位缺陷对磁性和电子结构的影响。${\mathrm{锰锑}}_{\mathrm{2个}}{特}_4$。Mn-Sb位置混合导致复杂的磁性结构，并调节反铁磁和铁磁之间的层间磁耦合。详细的非化学计量和现场混合${\mathrm{锰锑}}_{\mathrm{2个}}{特}_4$ 晶体取决于生长参数，这可能导致 $\approx 40％$ Sb和Mn占据的锰位点的百分比 $\approx 15％$晶体中Mn引起的Sb位置的变化。单晶中子衍射和电子显微镜研究显示反位缺陷几乎随机分布。能带结构计算表明，Mn-Sb位置混合有利于铁磁层间耦合，这与实验观察一致，但不利于非平凡拓扑结构的能带反转。我们的研究结果表明，Mn离子在Bi的Bi位点上具有远距离磁性。${\mathrm{锰铋}}_{\mathrm{2个}}{特}_4$。在由交替的磁层和拓扑层组成的所有分层异质结构中，应考虑到位混合的影响，包括整个$\mathrm{锰铁}（{双}_{\mathrm{2个}}{特}_3{）}_{ñ}$，其Sb类似物及其固体溶液。