Strong enhancement of spin–orbit torques and perpendicular magnetic anisotropy in Pt_0.75Ti_0.25/Co–Ni multilayer/Ta_n superlattices

We report the development of the Pt_0.75Ti_0.25/Co–Ni multilayer/Ta_n superlattice with strong spin–orbit torque, large perpendicular magnetic anisotropy, and remarkably low switching current density. We demonstrate that the efficiency of the spin–orbit torque increases nearly linearly with the repetition number n, which is in excellent agreement with the spin Hall effect of the Pt_0.75Ti_0.25 being essentially the only source of the observed spin–orbit torque. The perpendicular magnetic anisotropy field is also substantially enhanced by more than a factor of 2 as n increases from 1 to 6. The Pt_0.75Ti_0.25/Co–Ni multilayers/Ta_n superlattice additionally exhibits deterministic, low-current-density magnetization switching despite the very large total layer thicknesses. The unique combination of strong spin–orbit torque, robust perpendicular magnetic anisotropy, low-current-density switching, and excellent high thermal stability makes the Pt_0.75Ti_0.25/Co–Ni multilayer/Ta_n superlattice a highly compelling material candidate for ultrafast, energy-efficient, and long-data-retention spintronic technologies.