Large spin current generation by the spin Hall effect in mixed crystalline phase Ta thin films

Manipulation of the magnetization in heavy-metal/ferromagnetic bilayers via the spin-orbit torque requires high spin Hall conductivity of the heavy metal. We measure inverse spin Hall voltage using a coplanar waveguide based broadband ferromagnetic resonance setup in the Py/Ta system with a varying crystalline phase of Ta. We demonstrate a strong correlation between the measured spin mixing conductance and spin Hall conductivity with the crystalline phase of Ta thin films. We found a large spin Hall conductivity of −2439(ℏ/e)Ω−1cm−1 for low-resistivity (68 μΩ cm) Ta film having mixed crystalline phase, which we attribute to an extrinsic mechanism of the spin Hall effect.