  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 energy density
($K_s = 2.7~erg/cm^2$), which is dominated by interfacial spin-orbit coupling
(ISOC) in the Pt/Co interface, total effective spin-mixing conductance
($G_{eff,tot} = 0.42 {\times} 10^{15}~{\Omega}^{-1} m^{-2}$) and two-magnon
scattering (${\beta}_{TMS} = 0.46~nm^2$) are first characterized, and the
damping-like torque (${\xi}_{DL}$ = 0.103) and field-like torque (${\xi}_{FL}$
= -0.017) efficiencies are also calculated quantitatively by varying the
thickness of the inserting Co layer. The significant enhancement of
${\xi}_{DL}$ and ${\xi}_{FL}$ 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.
