Visualization of Ferromagnetic Domains in Magnetic Topological Insulator-Iron Chalcogenide Heterostructures*

The interfacial superconductivity observed in heterostructures combining topological insulator (TI) and antiferromagnetic FeTe has attracted significant attention in recent years. In this work, we synthesized magnetic TI/FeTe heterostructures which exhibit a superconducting phase transition at T_c~12 K. Transport measurements reveal the presence of anomalous Hall hysteresis loops below the Curie temperature. Zero Hall resistance is observed as the sample transitions into the superconducting state below T_c. To confirm the ferromagnetism below the superconducting temperature, we employ cryogenic magnetic force microscopy (MFM) at 2.2 K with in-situ transport measurements. The evolution of domain nucleation and domain wall propagation in various magnetic fields in the zero-resistance state confirms the robust coexistence of ferromagnetic order with superconductivity. Based on the domain population, we can construct ferromagnetic hysteresis loops in the superconducting state. Furthermore, the corresponding coercive fields are in good agreement with those obtained from reflective magnetic circular dichroism (RMCD) measurements.