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  1. More than a decade after the first theoretical and experimental studies of the spin Hall conductivity (SHC) of Pt, both its dominant origin and amplitude remain in dispute. We report the experimental determination of the rapid variation of the intrinsic SHC of Pt with the carrier lifetime (τ) in the dirty-metal regime by incorporating finely dispersed MgO intersite impurities into the Pt, while maintaining its essential band structure. This conclusively validates the theoretical prediction that the SHC in Pt in the dirty-metal regime should be dominated by the intrinsic contribution, and should decrease rapidly with shortening τ. When interfacial spin backflow is taken into account, the intrinsic SHC of Pt in the clean limit is at least 1.6 × 10 6 (ℏ/2 e ) ohm −1 m −1 , more than 3.5 times greater than the available theoretical predictions. Our work also establishes a compelling spin Hall metal Pt 0.6 (MgO) 0.4 with an internal giant spin Hall ratio of 0.73.
  2. Increasing dampinglike spin-orbit torque (SOT) is both of fundamental importance for enabling new research into spintronics phenomena and also technologically urgent for advancing low-power spin-torque memory, logic, and oscillator devices. Here, we demonstrate that enhancing interfacial scattering by inserting ultra-thin layers within a spin Hall metals with intrinsic or side-jump mechanisms can significantly enhance the spin Hall ratio. The dampinglike SOT was enhanced by a factor of 2 via sub-monolayer Hf insertion, as evidenced by both harmonic response measurements and current- induced switching of in-plane magnetized magnetic memory devices with the record low critical switching current of ~73 μA (switching current density ≈ 3.6×106 A/cm2). This work demonstrates a very effective strategy for maximizing dampinglike SOT for low-power spin-torque devices.