Low power spin-orbit torque switching in sputtered BiSb topological insulator/perpendicularly magnetized CoPt/MgO multilayers on oxidized Si substrate

Topological insulators (TIs) are promising for efficient spin current sources in spin-orbit torque (SOT) magnetoresistive random access memory (MRAM). However, TIs are usually deposited by molecular beam epitaxy on single crystalline III-V semiconductor or sapphire substrates, which are not suitable for realistic applications. Here, we studied SOT characteristics in sputtered BiSb topological insulator-Pt/Co/Pt-MgO heterostructures deposited on oxidized Si substrates, where Pt/Co/Pt trilayers have a large perpendicular magnetic anisotropy field of 4.5 kOe. We show that the BiSb layer has a large effective spin Hall angle of theta(eff)(SH) = 2.4 and a high electrical conductivity of sigma = 1.0 x 10(5) Omega(-1) m(-1). The magnetization can be switched by a small current density of 2.3 x 10(6) A cm(-2) at a pulse width of 100 mu s, which is 1 or 2 orders of magnitudes smaller than those in heavy metals. Our work demonstrates the high efficiency and robustness of BiSb as a spin current source in realistic SOT-MRAM.