https://doi.org/10.1103/PhysRevB.106.L140407
We report strong enhancement of spin-orbit torques by incorporating Si3N4 impurities into the dirty metal Pt. We find that the Si3N4 impurities lower the spin Hall conductivity and the charge conductivity of the Pt host at different rates, leading to a twofold increase in the dampinglike spin-orbit torque per unit current density for ferrimagnetic Ptx(Si3N4)1–x/Co0.65Tb0.35 bilayers. This torque enhancement is attributed to the optimized trade-off between the intrinsic spin Hall conductivity and the spin carrier lifetime in the dirty limit. We also find that only 58% of the angular momentum of the spin current entering the ferrimagnetic Co0.65Tb0.35 relaxes via exchange interaction and thus makes a contribution to spin torque generation. This work establishes Pt0.7(Si3N4)0.3 with a high spin Hall ratio of 0.8 and a high charge conductivity of 1.2×106Ω−1m−1 as a compelling spin Hall metal for spin-orbitronics. This work also reaffirms the variation of the spin-orbit torque with relative spin relaxation rates within the magnetic layer.