Giant spin torque efficiency in naturally oxidized polycrystalline TaAs thin films

Abstract

We report the measurement of efficient charge-to-spin conversion at room temperature in Weyl semimetal/ferromagnet heterostructures with both oxidized and pristine interfaces. Polycrystalline films of the Weyl semimetal, TaAs, are grown by molecular beam epitaxy on (001) GaAs and interfaced with a metallic ferromagnet (Ni${}_{0.8}$Fe${}_{0.2}$). Spin torque ferromagnetic resonance (ST-FMR) measurements in samples with an oxidized interface yield a spin torque efficiency as large as ${\xi }_{\mathrm{FMR}}=0.45\pm 0.25$ for a 8 nm Ni${}_{0.8}$Fe${}_{0.2}$ layer thickness. By studying ST-FMR in these samples with varying Ni${}_{0.8}$Fe${}_{0.2}$ layer thickness, we extract a damping-like torque efficiency as high as ${\xi }_{\mathrm{DL}}=1.36\pm 0.66$. In samples with a pristine (unoxidized) interface, the spin torque efficiency has opposite sign to that observed in oxidized samples (${\xi }_{\mathrm{FMR}}=-0.27\pm 0.14$ for a 5 nm Ni${}_{0.8}$Fe${}_{0.2}$ layer thickness). We also find a lower bound on the spin Hall conductivity ($424\pm 110\frac{\hslash }{e}$ S/cm) which is surprisingly consistent with theoretical predictions for the single crystal Weyl semimetal state of TaAs.

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Cited by in corpus (5)

• Epitaxial growth and characterization of Bi${}_{1-x}$Sb${}_x$ thin films on (0001) sapphire substrates
• Thin film growth of the Weyl semimetal NbAs
• Exploration of growth conditions of TaAs Weyl semimetal thin film by pulsed laser deposition
• Spin Hall conductivity in Bi${}_{1-x}$Sb${}_x$ as an experimental test of bulk-boundary correspondence
• Uniting Weyl semimetals and semiconductors in a family of arsenides