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 (Ni0.8Fe0.2). Spin torque ferromagnetic resonance (ST-FMR) measurements in samples with an oxidized interface yield a spin torque efficiency as large as ξFMR = 0.45±0.25 for a 8 nm Ni0.8Fe0.2 layer thickness. By studying ST-FMR in these samples with varying Ni0.8Fe0.2 layer thickness, we extract a damping-like torque efficiency as high as ξDL = 1.36 ± 0.66. In samples with a pristine (unoxidized) interface, the spin torque efficiency has opposite sign to that observed in oxidized samples (ξFMR = −0.27±0.14 for a 5 nm Ni0.8Fe0.2 layer thickness). We also find a lower bound on the spin Hall conductivity (424 ± 110 ℏ/e S/cm) which is surprisingly consistent with theoretical predictions for the single crystal Weyl semimetal state of TaAs.

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 (Ni0.8Fe0.2). Spin torque ferromagnetic resonance (ST-FMR) measurements in samples with an oxidized interface yield a spin torque efficiency as large as ξFMR = 0.45±0.25 for a 8 nm Ni0.8Fe0.2 layer thickness. By studying ST-FMR in these samples with varying Ni0.8Fe0.2 layer thickness, we extract a damping-like torque efficiency as high as ξDL = 1.36 ± 0.66. In samples with a pristine (unoxidized) interface, the spin torque efficiency has opposite sign to that observed in oxidized samples (ξFMR = −0.27±0.14 for a 5 nm Ni0.8Fe0.2 layer thickness). We also find a lower bound on the spin Hall conductivity (424 ± 110 ℏ/e S/cm) which is surprisingly consistent with theoretical predictions for the single crystal Weyl semimetal state of TaAs.

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 (Ni0.8Fe0.2). Spin torque ferromagnetic resonance (ST-FMR) measurements in samples with an oxidized interface yield a spin torque efficiency as large as ξFMR = 0.45±0.25 for a 8 nm Ni0.8Fe0.2 layer thickness. By studying ST-FMR in these samples with varying Ni0.8Fe0.2 layer thickness, we extract a damping-like torque efficiency as high as ξDL = 1.36 ± 0.66. In samples with a pristine (unoxidized) interface, the spin torque efficiency has opposite sign to that observed in oxidized samples (ξFMR = −0.27±0.14 for a 5 nm Ni0.8Fe0.2 layer thickness). We also find a lower bound on the spin Hall conductivity (424 ± 110 ℏ/e S/cm) which is surprisingly consistent with theoretical predictions for the single crystal Weyl semimetal state of TaAs.

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 (Ni0.8Fe0.2). Spin torque ferromagnetic resonance (ST-FMR) measurements in samples with an oxidized interface yield a spin torque efficiency as large as ξFMR = 0.45±0.25 for a 8 nm Ni0.8Fe0.2 layer thickness. By studying ST-FMR in these samples with varying Ni0.8Fe0.2 layer thickness, we extract a damping-like torque efficiency as high as ξDL = 1.36 ± 0.66. In samples with a pristine (unoxidized) interface, the spin torque efficiency has opposite sign to that observed in oxidized samples (ξFMR = −0.27±0.14 for a 5 nm Ni0.8Fe0.2 layer thickness). We also find a lower bound on the spin Hall conductivity (424 ± 110 ℏ/e S/cm) which is surprisingly consistent with theoretical predictions for the single crystal Weyl semimetal state of TaAs.