Interfacial spin Hall effect and spin swapping in Fe-Au bilayers from first principles

Abstract

The interfaces in hybridized structures usually give rise to rich phenomena, which open the way to novel devices with extraordinary performance. Here, we investigate the interface-related spin transport properties in $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Au}$ bilayers based on first-principles calculations. We find that the spin Hall current in the Au side near the interface flows in the opposite direction to the bulk spin Hall current with the magnitude sensitive to the magnetization direction of Fe. This interfacial contribution is attributed to the spin-dependent transmission within a few atomic layers, where a strong interfacial Rashba spin-orbit coupling exists. Surprisingly, the interfacial spin Hall currents are found to be not confined at the interface but extend tens of nanometers. This length scale is found to be much shorter than the spin diffusion length and determined by momentum relaxation, instead of spin relaxation. The resistivity dependence of the bulk spin Hall angle implies the coexistence of different spin Hall mechanisms. In addition, the interfacial swapping spin currents, as a consequence of the spin precession under the interfacial Rashba field, are also obtained from our calculation and complete the full spin transport picture with all nonvanishing components. Our results suggest the importance of the interface engineering in spin-related transport in ferromagnetic-nonmagnetic heterostructures and the possibility of manipulating the interfacial transport by the magnetization orientation of the magnetic layer.