Generation of out-of-plane polarized spin current in (permalloy, Cu)/EuS interfaces

The generation of out-of-plane polarized spin current is crucial for efficiently manipulating perpendicularly magnetized systems used in high-density magnetic recording. Here, we demonstrate the generation of out-of-plane polarized spin current at room temperature using an insulator, EuS. By employing angleresolved spin-torque ferromagnetic resonance, we find a large unconventional out-of-plane torque conductivity, sigma zDL = -0.13 x 105( h over bar /2e) (S2 m)-1 in the Py(= Ni81Fe19)/EuS bilayer, which is comparable to the conventional in-plane dampinglike torque conductivity, sigma yDL. Additionally, a giant in-plane fieldlike torque (sigma zFL) with a magnitude of 27 times larger than that of the conventional out-of-plane fieldlike torque (sigma yFL) is also observed in the Py/EuS bilayer. The unconventional torques due to the out-of-plane polarized spin current (sigma zDL and sigma zFL) persist even by inserting a 10-nm-thick Cu layer between Py and EuS. Our findings demonstrate that the unconventional torques in these systems originate from the interfaces through spin swapping and/or spin-orbit precession mechanisms.