XMCD study of intrinsic magnetic topological insulator hetero/sandwich structures II: the role of impurities

Intrinsic magnetic topological insulator (TI) heterostructures, in which a magnetic Mn monolayer is embedded inside the topmost TI layer, are systems that inherently possess both magnetism and topologically nontrivial properties and was first experimentally fabricated by the present proposer Toru Hirahara in 2017. This breakthrough led to a significant enhancement of the temperature to realize the quantum anomalous Hall effect, which is expected to be useful in developing dissipation-less devices. Until now, we have fabricated MnBi2Se4/Bi2Se3 (MBT/BS), and MnBi2Te4/Bi2Te3 (MBT/BT) systems and studied their intriguing magnetic properties in relation to the gapped surface-state Dirac cone (DC) dispersion. In the previous proposal (2023027296), we aimed to extend this research from heterostructures to sandwich structures which host two magnetic Mn layers and clarify the how the DC surface states are involved in the magnetic interaction of the two Mn monolayers. First, the aim of the present proposal it to make a follow-up of this previous proposal following our first machine time in the middle of September. We will perform XMCD measurements at the Mn L edge for the MBS/(BS)N/MBS or MBT/(BT)N/MBT sandwich structures with different N. We will also determine the role of the nonmagnetic element Bi and Te or Se by measuring the XMCD at respective absorption edges. Secondly, we hope to clarify the role of Mn defects in these systems (Mn intermixed with Bi and Mn at the vdW gap) by characterize the magnetic properties (the XMCD spectral shape, Curie temperature, coercive field …) for samples with different impurity concentration. By combining XMCD and ARPES data as well as theoretical calculation of the band structure and the XMCD spectra, we expect to clarify the magnetic coupling between Mn atoms at different environments as well as the intricate relationship between the DC band dispersion and magnetic properties of intrinsic TIs.