Role of Magnetic Defects in Tuning Ground States of Magnetic Topological Insulators

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 Bi2Se3‐based dilute ferromagnetic (FM) TIs and MnBi2Te4 (MBT)‐based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scattering data show that a fraction of the Mn defects in Sb2Te3 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 (Sb1−xMnx)2Te3 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.

Antisite-Defects Control of Magnetic Properties in MnSb2Te4

“…The FM Mn Sb –Mn Sb interlayer interactions can be proved in Mn-doped Sb 2 Te 3 and Bi 2 Te 3 . Previous studies have reported that these compounds exhibited an FM ground state, and their magnetic orders were confirmed by neutron scatting measurements. ,− …”

“…At least 60 T is required to break the AFM interactions . Neutron diffraction measurements and DFT calculations have shown that J 2 can be significantly enhanced by increasing the Mn Sb content. , J 3 is a positive value. The FM Mn Mn –Mn Mn intralayer coupling makes the SL a two-dimensional ferromagnet.…”

Enhancing MnBi2Te4 Stability by Doping

“…As and Sb dopants on the Bi site of MBT have been well studied. 47,48,100,101 Sb dopants on Bi sites of MnBi 4 Te 7 and MBT are known to increase antisite defect concentrations, 100,102 as evidenced by theoretical calculations showing reduced antisite defect formation energies. 78 Simple periodic table trends and atomic size arguments can explain the decrease in the mixed Mn−Bi antisite formation energy with As doping at Bi sites.…”

Relationship between disorder, magnetism and band topology in Mn(Sb1–x Bi x )2Te4 single crystals

“…Previous study shows that the occupations of Mn Mn and Mn Sb/Bi have a strong influence on the magnetic ground states of these systems. [15,26] First, the interblock interaction between Mn Mn is AFM intrinsically. Second, the intrablock interaction between Mn Mn and Mn Sb/Bi is also AFM when the interblock Mn Sb/Bi is coupled ferromagnetically.…”

“…Second, the intrablock interaction between Mn Mn and Mn Sb/Bi is also AFM when the interblock Mn Sb/Bi is coupled ferromagnetically. [26] Thus, the higher Mn Sb/Bi in samples with x ≤ 0.1 could drive the system to the FM ground state. In contrast, the samples with higher Bi content, in which the Mn Sb/Bi are lower, will have an AFM ground state.…”