Large Damping-like Spin–Orbit Torque and Improved Device Performance Utilizing Mixed-Phase Ta

The β phase of Ta is known to exhibit higher spin Hall efficiency compared to other heavy metals such as Pt. However, the larger resistivity of β-phase Ta leads to higher power consumption for spin–orbit torque (SOT)-based devices. In this work, we measure the efficiency of damping-like torque and field-like torque in Ni80Fe20/Ta using spin-torque ferromagnetic resonance technique. We report a larger damping-like torque efficiency of −(0.52 ± 0.01) for Ni80Fe20/Ta with low-resistive mixed (α + β)-phase Ta, which is about 40% larger compared to β-phase Ta. The field-like torque efficiency is found to be lower (by ≈400%) and of opposite sign compared to β-phase Ta. The estimated power consumption is found to be lower in the mixed-phase Ta system compared to the β-phase Ta as well as some Pt-based systems. Using micromagnetic simulations, we show that the measured values of damping-like torque and field-like torque for mixed-phase Ta lead to improved device performance, namely, (i) a lower switching time in a nanopillar-based SOT device and (ii) improved phase noise in a nanoconstriction-based spin Hall nano-oscillator.