Evolution of spin Hall mechanism and spin–orbit torque in ( α , β ) phase tantalum film

We investigate the spin Hall mechanism and spin–orbit torque (SOT) efficiency in Ta/CoFeB/MgO heterostructures with varying Ta crystalline phases. The Ta crystalline phase, specifically (α + β) mixed phase and β phase, is achieved by controlling the sputtering power (PTa) during Ta deposition. We observe a negative temperature coefficient of resistivity for Ta deposited at PTa ≥ 40 W, which corresponds to the β phase of Ta. Our phenomenological scaling law analysis reveals a significant contribution of skew scattering to the spin Hall effect (SHE) in β phase Ta. Furthermore, we conduct a comprehensive comparison of the critical switching current density of Ta (JCTa) and power consumption between (α + β) Ta and β Ta phases. Despite β Ta exhibiting higher resistivity, its power consumption remains lower than that of (α + β) Ta phase, suggesting that β Ta is a superior spin–orbit material. Our findings serve as a valuable reference for manipulating SOT and SHE mechanisms through crystalline phase engineering.