Strong enhancement of spin-orbit torques in ferrimagnetic Ptx(Si3N4)1-x/CoTb bilayers by Si3N4 doping

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 Pt-x(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 Pt-0.7(Si3N4)(0.3) with a high spin Hall ratio of 0.8 and a high charge conductivity of 1.2 x 10(6) Omega m(-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.

Automated summary

We report a strong enhancement of spin-orbit torques in dirty metal Pt by incorporating Si3N4 impurities. The enhancement is attributed to the optimized trade-off between the intrinsic spin Hall conductivity and the spin carrier lifetime in the dirty limit, resulting in a twofold increase in the dampinglike spin-orbit torque per unit current density in Pt-x(Si3N4)(1-x)/Co0.65Tb0.35 bilayers. We also find that only 58% of the angular momentum of the spin current contributes to spin torque generation.