Observation of large magnetoresistance switching in topological-insulator/ferromagnetic-metal heterostructure with perpendicular magnetic anisotropy

In the last decade, studies of magnetoresistance in heterostructures of topological insulator (TI) and ferromagnetic (FM) insulators have indicated the existence of induced magnetization at TI surfaces. However, the magnetic proximity effect in heterostructures of TIs and FM metals has been less explored. Here, we report a spin-valve-like magnetoresistance (MR) switching observed in a bilayer device of Bi₂Se₃ and a Co/Pt multilayer ([Co/Pt]), where the [Co/Pt] is a FM metal with a perpendicular magnetic anisotropy. This MR switching happens at temperatures below 1 K and for magnetic field sweeps along all in-plane and out-of-plane directions, at values much lower than the magnetization switching fields of the top FM layer. The in-plane field sweeps at various angles also reveal a threefold symmetry of the switching fields, matching the symmetry of the TI crystal structure. We suggest that the large MR switching rises from the interplay between the magnetization of the top FM metal layer and the induced magnetization at the TI surface.