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

Abstract

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 $\ensuremath{-}2439(\ensuremath{\hbar}/e){\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ for low-resistivity (68 $\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}$ cm) Ta film having mixed crystalline phase, which we attribute to an extrinsic mechanism of the spin Hall effect.