Fully relativistic first-principles quantum transport simulation of noncollinear spin transfer and spin Hall current

In this work, we report the fully relativistic (FR) first-principles quantum transport simulation of noncollinear spin transfer and spin Hall current in the device structure. In this method, the noncollinear FR exact muffin-tin orbital method is combined with Keldysh's nonequilibrium Green's function approach and mean-field theory to account for the multiple disorder scattering. We adopt the Bargmann-Wigner polarization operator to define the appropriate FR spin current so that the current-induced spin transfer, in the noncollinear magnetic device or due to the spin Hall effect, can be studied from first principles. As applications, we calculate the spin transfer torque in noncollinear spin valves Co/Cu/FM/Cu (FM = Co, Ni0.8Fe0.2) and spin Hall angles in various Pt1-xYx [Y = vacancy (Va), Au, Ag, Pd] alloys. We find that our FR results agree well with previous theoretical simulations and experimental measurements. Moreover, it is found that the applied finite bias can significantly enhance the spin Hall angle in Pt1-xVax, and PtAg alloy presents a much higher spin Hall angle than that of PtAu and PtPd alloys. Our implementation of the FR method provides an important first-principles tool for studying various nonequilibrium spin phenomena and the associated relativistic effects in realistic device structures with atomic disorders, including both current-induced spin transfer and spin-orbit torques.

Automated summary

In this work, the fully relativistic first-principles quantum transport simulation is used to study noncollinear spin transfer and spin Hall current. The method combines the noncollinear FR exact muffin-tin orbital method with Keldysh's nonequilibrium Green's function approach and mean-field theory to account for multiple disorder scattering. The Bargmann-Wigner polarization operator is adopted to define the appropriate FR spin current. The results agree well with previous theoretical simulations and experimental measurements.