Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers

We study inserting Co layer thickness-dependent spin transport and spin-orbit torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic resonance. The interfacial perpendicular magnetic anisotropy (IPMA) energy density (K_\rm s= 2.7 erg/cm^2, 1 erg = 10^-7 J), which is dominated by interfacial spin-orbit coupling (ISOC) in the Pt/Co interface, total effective spin-mixing conductance (G_\mathrmeff,tot^\mathrm\uparrow \downarrow =\mathrm0.42\times 10^15 \mathrm\Omega ^-1\cdot\mathrmm^-2) and two-magnon scattering (\beta_\mathrmTMS= 0.46 \mathrmnm^2) are first characterized, and the damping-like torque (\xi_\mathrmDL= 0.103) and field-like torque (\xi _\mathrmFL=-0.017) efficiencies are also calculated quantitatively by varying the thickness of the inserting Co layer. The significant enhancement of \xi_\mathrmDL and \xi_\mathrmFL in Pt/Co/Py than Pt/Py bilayer system originates from the interfacial Rashba-Edelstein effect due to the strong ISOC between Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a considerable out-of-plane spin polarization SOT, which is ascribed to the spin anomalous Hall effect and possible spin precession effect due to IPMA-induced perpendicular magnetization at the Pt/Co interface. Our results demonstrate that the ISOC of the Pt/Co interface plays a vital role in spin transport and SOTs-generation. Our finds offer an alternative approach to improve the conventional SOTs efficiencies and generate unconventional SOTs with out-of-plane spin polarization to develop low power Pt-based spintronic via tailoring the Pt/FM interface.