Highly efficient spin current source using BiSb topological insulator/NiO bilayers

BiSb is a topological insulator with both giant spin Hall effect and high electrical conductivity, which are important for ultralow power spin–orbit-torque magnetoresistive random access memory. However, when a ferromagnetic (FM) thin film is deposited on top of BiSb, large surface roughness and diffusion of Sb out of the BiSb layer into the FM layer results in a much smaller effective spin Hall angle θ SH eff . In this work, we show that by inserting a NiO layer between BiSb and Co, we can significantly improve θ SH eff of BiSb and induce perpendicular magnetic anisotropy at the NiO/Co interface. We obtained a large θ SH eff = 10.3 for the BiSb bottom layer at the NiO layer thickness of 3 nm, which is comparable to the best of BiSb top layer studied so far. Our study shows that BiSb/NiO bilayers are promising for integration of BiSb to SOT-MRAM.