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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 β-W, the metastable A15 structured variant of pure W, has charge-spin conversion efficiencies on par with Pt, and it was predicted that β-W/Ta alloys should be even more efficient. Here we demonstrate the enhancement of the spin Hall ratio (SHR) in A15-phase β-W films doped with Ta (W 4− x Ta x where x= 0.34±0.06) 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∼ 9% larger than pure β-W films. We also found that the SHR's in devices with Co 2 Fe 6 B 2 were nearly twice as large as the SHR's in devices with Co 4 Fe 4 B 2. This work shows that by optimizing deposition parameters and substrates, the fabrication of the optimum W 3 Ta alloy …