Strong Spin-Orbit Torque Induced by the Intrinsic Spin Hall Effect in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>Cr</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Pt</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:math>
Qianbiao Liu, Jingwei Li, Lujun Zhu, Xin Lin, Xinyue Xie, Lijun Zhu
Abstract
We report on a spin-orbit-torque study of the spin-current generation in ${\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Pt}}_{x}$ alloy, using the light 3d ferromagnetic Co as the spin-current detector. We find that the dampinglike spin-orbit torque of ${\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Pt}}_{x}/\mathrm{Co}$ bilayers can be enhanced by tuning the $\mathrm{Cr}$ concentration in the ${\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Pt}}_{x}$ layer, with a maximal value of 0.31 at the optimal composition of ${\mathrm{Cr}}_{0.2}{\mathrm{Pt}}_{0.8}$. The mechanism and the efficiency of spin-current generation in the ${\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Pt}}_{x}$ alloy can be fully understood by the characteristic trade-off between the intrinsic spin Hall conductivity of $\mathrm{Pt}$ and the spin carrier lifetime in the dirty limit. This suggests that $\mathrm{Cr}$ is simply as effective as other metals, oxides, and nitrides (e.g., $\mathrm{Hf}$, $\mathrm{Au}$, $\mathrm{Pd}$, $\mathrm{Cu}$, $\mathrm{Ti}$, $\mathrm{Mg}\mathrm{O}$, and ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$) in enhancing the dampinglike spin-orbit torque generated by the spin Hall effect of a $\mathrm{Pt}$ host via strengthening the spin carrier scattering and that alloying $\mathrm{Pt}$ with $\mathrm{Cr}$ does not employ observable spin-current generation via additional spin Hall effect, orbital Hall effect, or interfacial spin-orbit coupling effects. This work also establishes the low-resistivity ${\mathrm{Cr}}_{0.2}{\mathrm{Pt}}_{0.8}$ as an energy-efficient spin-orbit-torque provider for magnetic memory and computing technologies.