Abstract
The van der Waals compound, MnBi2Te4, 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 MnSb2Te4 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 MnSb2Te4. 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 MnSb2Te4 crystals depend on the growth parameters, which can lead to ≈40% of Mn sites occupied by Sb and ≈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 MnBi2Te4. 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 MnTe(Bi2Te3)n, its Sb analogs, and their solid solution.
| Original language | English |
|---|---|
| Article number | 021033 |
| Journal | Physical Review X |
| Volume | 11 |
| Issue number | 2 |
| DOIs | |
| State | Published - May 2021 |
Funding
The authors thank Huibo Cao, Maohua Du, Robert McQueeney, Satoshi Okamoto, and Xiaodong Xu for helpful discussions and Michael Lance for WDS measurements. Research at ORNL (M. A. M., B. C. S., and J. Y.) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Science and Engineering. L.-L. W. was supported by the Center for the Advancement of Topological Semimetals, an Energy Frontier Research Center funded by U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358. Q. Z. acknowledges support from the Gordon and Betty Moore Foundations EPiQS Initiative, Grant No. GBMF9069. The STM work at Rutgers was supported by ARO Grant No. W911NF2010108. M. C. is supported by an Early Career project supported by DOE Office of Science. A portion of this research used resources at the High Flux Isotope Reactor, Spallation Neutron Source and the Center for Nanophase Materials Sciences, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory.