and a ferromanget with perpendicular magnetic anisotropy*

Topological insulators (TIs) have insulating bulk states and topologically protected gapless boundary states that exhibit spin momentum locking and prohibited backscattering. Such unusual properties of topological surface states (SSs) in three dimensional TIs make the material much favorable for spintronic applications. However, the properties of these SSs can be largely modified in the presence of ferromagnetism in out-of-plane direction which breaks the time reversal symmetry. We report magnetoresistance (MR) signals in a heterostructure of 3D TI Bi₂Se₃ and Co/Pt multilayer with perpendicular magnetic anisotropy. In particular, the abrupt switching between the high and low MR states was observed for temperature lower than 1K and for field along in-plane and out-of-plane directions. This MR is incompatible with the magnetization behavior of the ferromagnetic layer and thus attributed to the magnetic ordering in the TI. Our observations indicate the possible existence of proximity magnetized SSs in Bi₂Se₃ with out-of-plane spin component.