Highly efficient spin-current generation from Pt/Ru multilayers

Increasing spin Hall angle of heavy metals has attracted considerable attention due to their potential applications in spintronic technology. Here, we demonstrate that the spin Hall angle could be enhanced dramatically in the Ta/[Pt/Ru]n/Pt/Co/Ta multilayers. The spin Hall angle reaches a maximum value of 0.28 when n = 5 from the loop-shift method with a relative low resistivity of approximately 48 μΩ cm. Meanwhile a minimum critical switching current density approximately 3.2 × 106 A/cm2 under an in-plane bias magnetic field around 5% of the perpendicular anisotropy field was obtained for the sample with n = 5 in current-induced magnetization switching experiment. We find that the extrinsic spin Hall mechanism changes from the spin skew scattering when n < 2 to spin side-jump mechanism when n > 2. This work provides an effective way in increasing spin Hall angle for low-power consumption spintronics devices.