Spin–orbit torque in perpendicularly magnetized Pt/Ni multilayers

The performance of spin–orbit torque (SOT) in heavy metal/ferromagnetic metal periodic multilayers has attracted widespread attention. In this paper, we have successfully fabricated a series of perpendicular magnetized Pt(2–t)/Ni(t)₄ multilayers, and studied the SOT in the multilayers by varying the thickness of Ni layer t. The current induced magnetization switching was achieved with a critical current density of 1 × 10⁷ A/cm². The damping-like SOT efficiency ξ_DL was extracted from an extended harmonic Hall measurement. We demonstrated that the ξ_DL can be effectively modulated by t_Pt/t_Ni ratio of Pt and Ni in the multilayers. The SOT investigation about the Pt/Ni_N multilayers might provide new material candidates for practical perpendicular SOT-MRAM devices.