Direct evidence of induced magnetic moment in Se and the role of misplaced Mn in MnBi2Se4-based intrinsic magnetic topological insulator heterostructures

Intrinsic magnetic topological insulators, in which magnetism and topology are inherently combined, are excellent systems to realize exotic phenomena such as the quantum anomalous Hall effect. However, there are many reports that show that the experimental samples are not so ideal and the effect of the unintentional disorder in these systems needs to be considered carefully. In this study, we investigate the role of misplaced magnetic atoms as well as nonmagnetic elements in the intrinsic magnetic topological insulator heterostructures based on MnBi2Se4 and Bi2Se3. We find that Mn atoms are not only placed at the central layer of the MnBi2Se4 septuple layer (SL) but also intermix with Bi (antisite Mn) as well as reside in the van der Waals (vdW) gap. Through a detailed comparison between the experimental and theoretical x-ray magnetic circular dichroism (XMCD) spectra, we find that the antisite Mn is coupled ferromagnetically, whereas the vdW Mn couple antiferromagnetically to the Mn in the central atomic plane of the SL. Furthermore, we detect a clear XMCD signal in nonmagnetic Se, providing unambiguous evidence of its magnetic interaction with Mn.