  Electrical control of magnetization is of crucial importance for integrated
spintronics devices. Spin-orbit torques (SOT) in heavy-metal/ferromagnetic
heterostructures have emerged as promising tool to achieve efficiently
current-induced magnetization reversal. However, the microscopic origin of the
SOT is being debated,with the spin Hall effect (SHE) due to nonlocal spin
currents and the spin Rashba-Edelstein effect (SREE) due to local spin
polarization at the interface being the primary candidates. We investigate the
electrically induced out-of-equilibrium spin and orbital polarizations in pure
Pt films and in Pt/3d-metal (Co, Ni, Cu) bilayer films using ab initio
electronic structure methods and linear-response theory. We compute
atom-resolved response quantities that allow us to identify the induced
spin-polarization contributions that lead to fieldlike SOTs, mostly associated
with the SREE, and dampinglike (DL) SOTs, mostly associated with the SHE, and
compare their relative magnitude, dependence on the magnetization direction, as
well as their Pt-layer thickness dependence. We find that both the FL and DL
components contribute to the resulting SOT at the Pt/Co and Pt/Ni interfaces,
with the former contributions being larger at the Pt interface layer and the
latter larger in the Co or Ni layers. Our calculations show that the
electrically-induced transverse orbital polarization is exceedingly larger than
the induced spin polarization and present even without spin-orbit coupling, in
contrast to the spin polarization.
