Giant, Linearly Increasing Spin–Orbit Torque Efficiency in Symmetry-Broken Spin–Orbit Torque Superlattices

Abstract

Magnetic heterostructures with high spin–orbit torque efficiency and low impedance have great promise for low-power spintronic technologies. We report a symmetry-broken spin–orbit superlattice [Pt0.75Cu0.25/Co/Ta] n , in which the dampinglike spin–orbit torque efficiency accumulates linearly with the repeat number n and achieves a giant value of >200% when n = 16, which is 100 times stronger than that of a conventional magnetic heterostructure with a clean Pt (e.g., 2% at a resistivity of 7 μΩ cm). The giant spin–orbit torque effect arises predominantly from the spin Hall effect of Pt0.75Cu0.25. The anomalous Nernst effect increases remarkably as the repeat number n increases, implying a critical need to include the thermal effect in the analysis of magnetic superlattices and multilayers. The giant spin–orbit torque, low resistivity, and strong anomalous Nernst effect suggest the great potential of the superlattice [Pt0.75Cu0.25/Co/Ta] n for low-power memory and logic technologies as well as high-performance thermoelectric battery and sensor applications.