Topological Insulator/Magnetic Insulator: a Platform for Efficient Spin Current Transport

Peng Li, Auburn University

March 27, 2020

Topological insulators (TIs) hold great promise for spintronic devices due to their large charge-to-spin conversion efficiency. It has been demonstrated that a TI can induce a spin-orbit torque and switch the magnetization of a neighboring ferromagnetic metal. However, it is unclear whether this is related to the exotic topological surface state (TSS) because the electrons from the ferromagnetic metal can suppress the TSS. In this talk, we discuss experiments that identified bona fide surface state-induced spin-orbit torques in topological insulator/magnetic oxide heterostructures. In a bilayer structure of Bi2Se3/BaFe12O19, a large spin-orbit torque from Bi2Se3 was able to switch the magnetization of BaFe12O19 up and down. When the magnetization was switched by a magnetic field, a current in Bi2Se3 can reduce the switching field by about 4000 Oe. The switching efficiency at 3 K is 300 times higher than at room temperature. When BaFe12O19 is replaced with Mg(Al,Fe)2O4, highly efficient spin pumping in the bulk-dominated regime was found at room temperature. These results highlight the promise of topological insulator/ferromagnetic insulating oxide bilayers as a platform for studying topological surface states in the context of spin-to-charge conversion.

Anomalous Hall effect measures in a topological insulator/magnetic insulator bilayer