One of the main challenges in spintronics research is to provide a link between magnetic elements and conventional electronic circuits. A novel approach to this old problem is to exploit the spin-orbit-interaction between the spin angular momentum and the orbital motion of electrons, generating a spin-orbit torque. Topological insulator based bilayers have been shown to provide particularly high spin-orbit torque efficiency but so far there is no experimental evidence correlating the interface structure about how the interface profile affects the spin-orbit-torque efficiency. In this proposal we seek to address this by combining the magnetic and depth sensitivity of PNR with ferromagnetic resonance measurements to probe the spin-transport.