Division of Materials Sciences and Engineering, Ames National Laboratory, Ames, IA, 50011, USA.
Department of Physics and Astronomy, Iowa State University, Ames, IA, 50011, USA.
Adv Mater. 2023 May;35(21):e2209951. doi: 10.1002/adma.202209951. Epub 2023 Mar 16.
Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi Se -based dilute ferromagnetic (FM) TIs and MnBi Te (MBT)-based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scattering data show that a fraction of the Mn defects in Sb Te form strong AFM dimer singlets within a quintuple block. The AFM superexchange coupling occurs via Mn-Te-Mn linear bonds and is identical to the AFM coupling between antisite defects and the FM Mn layer in MBT, establishing common interactions in the two materials classes. It is also found that the FM correlations in (Sb Mn ) Te are likely driven by magnetic defects in adjacent quintuple blocks across the van der Waals gap. In addition to providing answers to long-standing questions about the evolution of FM order in dilute TI, these results also show that the evolution of global magnetic order from AFM to FM in Sb-substituted MBT is controlled by defect engineering of the intrablock and interblock coupling.
磁性缺陷在磁性拓扑绝缘体（TI）中起着重要但尚未被充分理解的作用。例如，拓扑表面输运和体磁性质受到基于 Bi Se 的稀磁（FM）TI 和基于 MnBi Te（MBT）的反铁磁（AFM）TI 中磁性缺陷的控制。尽管 Sb Te 中的 Mn 缺陷具有初生铁磁性，但非弹性中子散射数据表明，在五重块内，一部分 Mn 缺陷形成了强 AFM 二聚单态。AFM 超交换耦合通过 Mn-Te-Mn 线性键发生，与 MBT 中反位缺陷与 FM Mn 层之间的 AFM 耦合相同，在这两种材料中建立了共同的相互作用。此外，还发现（Sb Mn）Te 中的 FM 相关性很可能是由范德华间隙中相邻五重块中的磁性缺陷驱动的。这些结果不仅为稀磁 TI 中 FM 序演化的长期问题提供了答案，还表明 Sb 取代的 MBT 中从 AFM 到 FM 的全局磁序演化是由块内和块间耦合的缺陷工程控制的。
