Spin-Orbit Torque Modulated by Interface Chemistry in Topological BiSb/NiFe Bilayers with Titanium Insertion

Topological insulators are intriguing materials in the field of spintronics because they exhibit unique electronic properties that hold great promise for device applications. BiSb has attracted more research interest among topological materials due to its remarkably high spin-orbit torque (SOT) efficiency. However, due to the low melting point of the alloy, high diffusivities of Bi/Sb tend to degrade the SOT efficiency with temperature and aging. In this work, we utilize interfacial chemistry driven by a titanium (Ti) spacer between BiSb and NiFe bilayers to improve the SOT efficiency. We investigated the effect of the Ti insertion layer on the SOT efficiency under as-deposited, room-temperature aging, and annealing conditions. The SOT efficiency, estimated from the spin-torque ferromagnetic resonance response, revealed that the samples with the Ti layer had shown a multifold increase in the SOT efficiency compared to those without Ti insertion. Atomic resolution microstructural analyses provided a clear understanding of the interfacial chemistry where Ti successfully hindered the interdiffusion of Ni and Sb. The interfacial chemistry in the vicinity of Ti contributed significantly to the improvement of the SOT efficiency. These results highlight the importance of the Ti insertion layer in the BiSb-based topological material/ferromagnet bilayer systems for SOT applications in spintronics.