Large spin Hall effect in room-temperature sputtered W₃Ta thin films grown on SiO₂ and Al₂O₃

The spin Hall effect (SHE), in non-magnetic (NM) metals with strong spin-orbit coupling (SOC) has received much attention due to potential technological applications like magnetic random-access memory (MRAM) and spin-logic devices. Large spin Hall angles (SHA, the ratio of J_s/J_c) have been observed in materials like Pt and the metastable phase, β-W (a.k.a. W₃W in the A15-structure). Recently, W₃Ta (and other A15 compounds) was theoretically predicted to host an even larger intrinsic SHE than β-W, originating from the large spin Berry curvature of its electronic band structure. Here we report the SHE of W_4-xTa_x films including W₃Ta, deposited by DC magnetron co-sputtering on SiO₂ and Al₂O₃ substrates. Spin-torque ferromagnetic resonance (ST-FMR) and optically detected ferromagnetic resonance (ODFMR) techniques were used to measure the SHA of various W_4-xTa_x compositions and thicknesses with CoFeB as the magnetic layer. We find that W₃Ta in the A15 structure could be stabilized on both types of substrates at room temperature and hosts a large SHA in W₃Ta similar to theoretical predictions opening the door to facile device fabrication of Pt-free spintronic devices.