Observation of interface-induced nonlocal spin-torques from Gd/Pt interface

We investigate spin–orbit torques (SOTs) generated by Gd/Pt and Ti/Pt interfaces by performing spin-torque ferromagnetic resonance measurements at room temperature. We report a sizable spin-current created by the Gd/Pt interface, exhibiting the damping-like-torque efficiency per unit electric field, ξDLE=−8 ± 0.6×104ℏ2e(Ωm)−1 as observed in Gd(5 nm)/Pt(1.5 nm)/Py(3 nm-6 nm)/Pt(1.5 nm) heterostructures. This interface-induced spin-current is attributed to the vertical electric field produced by the broken structural inversion symmetry, with a work function difference of 2.75 eV between Gd and Pt. This is further substantiated by varying the thickness of the Gd-layer. We compare these results with the Ti/Pt interface, which has a work function difference of 1.3 eV, by implementing Ti(5 nm)/Pt(1.5 nm)/Py(3 nm-6 nm)/Pt(1.5 nm) heterostructures. We find that the spin-current induced by the Ti/Pt interface is too small to overcome the remnant SOTs caused by the asymmetrically grown Pt layers on both sides of Py. Our work reveals the role of interface-induced spin currents for practical applications, which can be leveraged to produce robust spin torques that complement the bulk spin-Hall torque.