Doping-induced spin Hall ratio enhancement in A15-phase, Ta-doped Beta-W thin films

As spintronic devices become more and more prevalent, the desire to find Pt free materials with large spin Hall effects is increasing. Previously it was shown that Beta W, the metastable A15 structured variant of pure W, has charge-spin conversion efficiencies on par with Pt, and it was predicted that Beta W(Ta) alloys should be even more efficient. Here we demonstrate the enhancement of the spin Hall ratio (SHR) in A15-phase Beta W films doped with Ta (W(4-x)Tax where x is between 0.28 and 0.4, deposited at room temperature using DC magnetron co-sputtering. In close agreement with theoretical predictions, we find that the SHR of the doped films was approx. 9 percent larger than pure Beta W films. We also found that the SHRs in devices with Co2Fe6B2 were nearly twice as large as the SHRs in devices with Co4Fe4B2. This work shows that by optimizing deposition parameters and substrates, the fabrication of the optimum W3Ta alloy should be feasible, opening the door to commercially viable, Pt free, spintronic devices.