${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ (MBT) is a promising van der Waals layered antiferromagnetic (AFM) topological insulator that combines a topologically nontrivial inverted Bi-Te band gap with ferromagnetic (FM) layers of Mn ions. The inelastic neutron scattering on single crystals reported here describes rather complex magnetism in MBT. The magnetic anisotropy that controls the bulk and surface magnetic field response of MBT is found to have contributions from both single-ion and interlayer two-ion terms. A description of the quasi-two-dimensional intralayer FM spin waves requires long-range, competing FM and AFM interactions and anomalous damping. While this might suggest carrier-mediated magnetic coupling, $\mathit{ab}\mathit{initio}$ calculations in insulating MBT also find long-range interactions, and classical spin dynamics simulations suggest that magnetic vacancies are at least partially responsible for observations of anomalous damping near the zone boundary.

中文翻译：

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磁性拓扑绝缘体MnBi2Te4中的准二维铁磁性和各向异性层间耦合

${\mathrm{锰铋}}_2{特}_4$(MBT) 是一种很有前途的范德华层状反铁磁 (AFM) 拓扑绝缘体，它结合了拓扑上非平凡的倒 Bi-Te 带隙与 Mn 离子的铁磁 (FM) 层。这里报道的单晶上的非弹性中子散射描述了 MBT 中相当复杂的磁性。发现控制 MBT 的体和表面磁场响应的磁各向异性具有来自单离子和夹层双离子项的贡献。准二维层内 FM 自旋波的描述需要长距离、竞争性 FM 和 AFM 相互作用以及异常阻尼。虽然这可能表明载流子介导的磁耦合，$\mathit{AB}\mathit{从头开始}$ 绝缘 MBT 中的计算也发现了长程相互作用，经典自旋动力学模拟表明磁空位至少部分负责观察区域边界附近的异常阻尼。