Quantum Anomalous Hall Effect and Exchange Interaction between Magnetic Topological Insulator and Antiferromagnetic Insulator*

Integration of a quantum anomalous Hall (QAH) insulator with a magnetically ordered material provides an additional degree of freedom to manipulate the magnetic orders and exotic quantum states. Here, we report molecular beam epitaxy (MBE) growth of high quality magnetically doped topological insulator (MTI) and the observation of QAH effect on an antiferromagnetic insulator Cr₂O₃. The exchange coupling between the two materials is investigated using field-cooling-dependent magnetometry and polarized neutron reflectometry. Exchange bias is observed when the sample is field-cooled under an out-of-plane magnetic field, and polarized neutron reflectometry reveals an exchange spring-like magnetic depth profile when the system is magnetized within the film plane. Both techniques show strong interfacial interaction between the antiferromagnetic order of the Cr₂O₃ and the magnetic topological insulator. The exchange interaction between MTI and adjacent antiferromagnetic insulators enables the effective manipulation of the magnetic and topological order in the topological insulator films.