Abstract
We report on a systematic comparative study of the spin Hall efficiency between highly face-centered cubic (fcc)-textured Pt–Al alloy films grown on MgO(001) and poorly crystallized Pt–Al alloy films grown on SiO2. Using CoFeB as the detector, we show that for Al compositions centering around x = 25, mainly L12-ordered Pt100−xAlx alloy films grown on MgO exhibit outstanding charge-spin conversion efficiency. For the Pt78Al22/CoFeB bilayer on MgO, we obtain damping-like spin Hall efficiency as high as ξDL ∼ +0.20 and expect up to a sevenfold reduction in power consumption compared to the polycrystalline bilayer of the same Al composition on SiO2. This work demonstrates that improving the crystallinity of fcc Pt-based alloys is a crucial step for achieving large spin Hall efficiency and low power consumption in this material class.
Highlights
In a nonmagnetic material (NM)/ferromagnetic material (FM) bilayer heterostructure with strong spin–orbit coupling, the application of an in-plane charge current leads to the generation of a transverse spin current and accumulation of non-equilibrium spin density near the NM/FM interface via either the “bulk” spin Hall effect (SHE)19 or the interfacial Rashba–Edelstein effect20,21 or spin-momentum locking of the topological surface states
We focus on fcc-based L12-Pt3Al and body-centered cubic-based B2-PtAl, for which the structures are illustrated in Figs. 1(a) and 1(b), respectively
We have studied the Al concentration xdependence of spin Hall efficiency and power consumption efficiency for Pt100−xAlx/CoFeB bilayers grown on two different substrates (MgO or SiO2)
Summary
Current-induced spin–orbit torque (SOT) is a promising means for manipulating the magnetization of a nanomagnet and for developing next-generation magnetic memories. In a nonmagnetic material (NM)/ferromagnetic material (FM) bilayer heterostructure with strong spin–orbit coupling, the application of an in-plane charge current leads to the generation of a transverse spin current and accumulation of non-equilibrium spin density near the NM/FM interface via either the “bulk” spin Hall effect (SHE) or the interfacial Rashba–Edelstein effect or spin-momentum locking of the topological surface states. The accumulated spin can be absorbed by the FM, exerting damping-like and field-like SOT to the magnetization. The accumulated spin can be absorbed by the FM, exerting damping-like and field-like SOT to the magnetization. This charge-to-spin conversion process is commonly expressed by the relation jDspLin(,FFLM) =. ΞDL(FL) describes phenomenologically the conversion efficiency based on the total spin current eventually absorbed by the FM for SOT generation, ignoring its origin (e.g., SHE or other interfacial mechanisms) and its transmission probabilities across the interface (e.g., spin backflow and spin memory loss).. For the NM/FM bilayer relevant for most applications, one should include the power dissipation due to the unavoidable current flow within the FM layer (with a thickness tFM and resistivity ρFM), leading to the power efficiency parameter η
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