Role of Magnetic Defects and Defect-engineering of Magnetic Topological Insulators

TL;DR

This paper investigates how magnetic defects influence the magnetic and topological properties of topological insulators, revealing defect-driven magnetic interactions and the potential to engineer magnetic order through defect manipulation.

Contribution

It uncovers the role of magnetic defects in controlling magnetic order and surface transport in topological insulators, highlighting defect engineering as a tool for magnetic property tuning.

Findings

Mn defects form AFM dimer singlets in Sb2Te3

AFM superexchange occurs via Mn-Te-Mn bonds

Magnetic correlations are influenced by defects across layers

Abstract

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$_2$Se$_3$-based dilute ferromagnetic (FM) TIs and MnBi$_2$Te$_4$ (MBT)-based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, our inelastic neutron scattering data show that a fraction of the Mn defects in Sb$_2$Te$_3$ 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. We also find that the FM correlations in (Sb$_{1-x}$Mn$_x$)$_2$Te$_3$ 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.