Efficient Spin-Orbit Torque Generation in Semiconducting WTe with Hopping Transport.

Spin-orbit torques (SOTs) from transition metal dichalcogenide systems (TMDs) in conjunction with ferromagnetic materials are recently found to be attractive in spintronics for their versatile features. However, most of the previously studied crystalline TMDs are prepared by mechanical exfoliation, which limits their potentials for industrial applications. Here, we show that amorphous WTe heterostructures deposited by magnetron sputtering possess a sizable damping-like SOT efficiency of ξ ≈ 0.20 and low damping constant of α = 0.009 ± 0.001. Only an extremely low critical switching current density of ≈ 7.05 × 10 A/m is required to achieve SOT-driven magnetization switching. The SOT efficiency is further proved to depend on the W and Te relative compositions in the co-sputtered WTe samples, from which a sign change of ξ is observed. In addition, the electronic transport in amorphous WTe is found to be semiconducting and is governed by a hopping mechanism. With the above advantages and rich tunability, amorphous and semiconducting WTe serves as a unique SOT source for future spintronics applications.