XMCD study of intrinsic magnetic topological insulator hetero/sandwich structures

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. These systems are also interesting in terms of two-dimensional (2D) magnetism.

In the present study, we aim 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, 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 at various temperature and magnetic fields to observe magnetic hysteresis curves and deduce the Curie temperature. Quantitative analysis of the obtained data will determine the magnetic moment of Mn. Secondly, we will determine the role of the nonmagnetic element Bi and Te or Se by measuring the XMCD at respective absorption edges. We have done preliminary measurements at BL23SU of SPring-8, Japan, and have succeeded in observing clear XMCD signals at the Se L edge. For both measurements, we hope to obtain better data with high S/N ratio at BL29 BOREAS. By combining the present XMCD experiments with ARPES data, we expect to clarify the intricate relationship between the DC band dispersion and magnetic properties of intrinsic TIs.