We study the damping-like spin–orbit torque (DL-SOT) efficiencies in W/Pt/Co/Pt multilayer structures by the current-induced hysteresis loop shift measurement and current-induced magnetization switching measurement. It is known that transition metals W and Pt possess spin Hall ratios with opposite signs, and therefore, the DL-SOT efficiencies in these multilayer structures may become zero with a certain W/Pt thickness combination. In this work, we show that indeed the zero DL-SOT efficiency can be achieved in such a structure, and the efficiency can evolve from negative (W-dominated) to positive (Pt-dominated) depending on the relative thickness of W and Pt. More importantly, we did not observe field-free switching when the W/Pt combination gives zero DL-SOT efficiency, which is in contrast to a recent report [Ma et al., Phys. Rev. Lett. 120, 117703 (2018)]. By further considering a simple spin diffusion model, we find that DL-SOT efficiencies ξDLPt=0.12 and ξDLW=−0.13 for the Pt and W layer, respectively, in our multilayer system. We also show that the Pt(2)/Co(0.5)/Pt(2) symmetric structure is a robust perpendicular magnetization anisotropy multilayer that can be employed on W or other spin Hall materials to characterize their DL-SOT efficiencies.
We report the incorporation behaviors of As, Sb, and N atoms in GaAsSbN grown by gas-source molecular-beam epitaxy. We found that N atom is more reactive and competitive than Sb atom at the growth temperature ranging from 420 to 450 1C. The increment in Sb beam flux hardly changes the N composition. However, the increment in N flux retards the incorporation of Sb. In addition, the increment in As 2 flux makes the Sb and N compositions decrease at the same rate. Based on these results, we have successfully grown GaAsSbN epilayers lattice-matched to GaAs substrates. The energy gap at room temperature is as low as 0.803 eV. Negative deviation from Vegard's law in lattice constant is observed in these layers.
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