Boosting Spin-Orbit-Torque Efficiency in Spin-Current-Generator/Magnet/Oxide Superlattices

Efficient manipulation of magnetic materials is essential for spintronics. In conventional spin-current-generator/magnet (SCG/M) bilayers, interfacial spin-orbit torques (SOTs) lose effectiveness in applica-tions that require large magnetic layer thicknesses to maintain magnetic anisotropy and stability at lateral sizes of tens of nanometers (e.g., magnetic tunnel junctions and racetrack nanowires). Here, we develop a universally workable three-dimensional spin-orbit material scheme in which the SOT efficiency can be remarkably boosted towards infinity by stacking [SCG/M /oxide]n superlattices, with the oxide layers breaking inversion symmetry. We demonstrate that this superlattice scheme promotes not only perpen-dicular magnetic anisotropy for an effectively rather thick magnetic layer but also enables switching of such thick magnetic layers by interfacial SOTs with n2 times lower power consumption than the corre-sponding conventional bilayer scheme with the same total thicknesses for the SCG and M. In contrast, we find that spin torque diminishes in second-type superlattices, [SCG/M]n, lacking inversion-symmetry breaking. These results provide an in-depth understanding of SOTs in magnetic multilayers and estab-lish [SCG/M /oxide]n superlattices as advantageous building blocks for the development of low-power, high-stability, and high-endurance spintronic memory and computing.

Automated summary

This article introduces a method for efficient manipulation of magnetic materials, in which the stacking of superlattices with inversion-symmetry breaking can significantly enhance the efficiency of spin-orbit torques. This method allows for the achievement of perpendicular magnetic anisotropy in thick magnetic layers and enables the switching of such layers with lower power consumption.