Determination of spin torque efficiencies in heterostructures with perpendicular magnetic anisotropy

Abstract

We report that by measuring a current-induced hysteresis loop shift versus in-plane bias magnetic field, the spin-Hall effect (SHE) contribution of the current-induced effective field per current density χ[subscript SHE] can be estimated for Pt- and Ta-based magnetic heterostructures with perpendicular magnetic anisotropy. We apply this technique to a Pt-based sample with its ferromagnetic (FM) layer being wedged deposited and discover an extra effective field contribution χ[subscript Wedged] due to the asymmetric nature of the deposited FM layer. We confirm the correlation between χ[subscript Wedged] and the asymmetric depinning process in FM layer during magnetization switching by magneto-optical Kerr microscopy. These results indicate the possibility of engineering deterministic spin-orbit torque switching by controlling the symmetry of domain expansion through the materials growth process.