Spin valve-like magnetoresistance of a topological insulator in proximity to a perpendicular magnet*

Topological insulators (TIs) have a variety of unique transport properties, one of which is symmetry-protected surface states. Efforts have been made to control the surface states by symmetry breaking via proximity magnetization, which is typically achieved by placing a ferromagnetic or antiferromagnetic insulator in direct contact with the TI. We report a spin valve-like magnetoresistance switching phenomena when the TI Bi2Se3 is in contact with a Co/Pt multilayer, which has a perpendicular magnetic anisotropy. The magnetoresistance is mostly isotropic, as evidenced by the resistance switching when either in-plane or out-of-plane magnetic fields are applied. This effect occurs at low temperatures, and the switching fields are incompatible with the behavior of Co/Pt. It appears the phenomenon is related to a magnetized TI surface and/or bulk states.