  Efficient manipulation of magnetic materials is essential for spintronics. In
spin-current generator/magnet bilayers, the efficiency of spin-orbit torques
per magnetic layer thickness scales inversely with the magnetic layer
thickness, leading to considerable power increase in applications with large
magnetic layer thickness. Here, we develop a 3D spin-orbit material scheme in
which the spin torque efficiency can be remarkably boosted up by stacking
[spin-current generator/magnet/oxide]n superlattices, with the oxide layers
breaking the inversion symmetry. In contrast, the spin torque diminishes in
[spin-current generator/magnet]n superlattices lacking inversion symmetry
breaking. These results advances the understanding of spin-orbit torques in
magnetic multilayers and establishes spin-current generator/magnet/oxide
superlattices as advantageous bricks for development of high energy-efficiency,
high-endurance, and high-density spintronic memory and computing.
