Linear Enhancement of Spin-Orbit Torque and Absence of Bulk Rashba Spin Splitting in Perpendicularly Magnetized Pt/Co/W_n Superlattices

The development of magnetic heterostructures with strong perpendicular magnetic anisotropy (PMA), strong spin-orbit torques (SOTs), low impedance, and good integration compatibility at the same time is central for high-performance spintronic memory and computing applications. Here, we report the development of the PMA superlattice Pt/Co/W_n that can be sputtered-deposited on commercial oxidized silicon substrates and has giant SOTs, strong uniaxial PMA of ≈ 9.2 Merg/cm³, and rigid macrospin performance. The damping-like and field-like SOTs of the Pt/Co/W_n superlattices exhibit a linear increase with the repeat number _n and reach the giant values of 225% and -33% (two orders of magnitude greater than that in clean-limit Pt) at _n = 12, respectively. The damping-like SOT is also of the opposite sign and much greater in magnitude than the field-like SOT, regardless of the number _n. These results clarify that the spin current that generates SOTs in the Pt/Co/W_n superlattices arises predominantly from the spin Hall effect rather than bulk Rashba spin splitting, providing a unified understanding of the SOTs in these superlattices. We also demonstrate deterministic switching in thickerthan-50-nm PMA Pt/Co/W12 superlattices at a low current density. This work establishes the Pt/Co/W_n superlattice as a compelling material candidate for ultra-fast, low-power, long-retention nonvolatile spintronic memory and computing technologies.