Giant Dampinglike-Torque Efficiency in Naturally Oxidized Polycrystalline TaAs Thin Films

Wilson Yanez, Yongxi Ou, Run Xiao, Supriya Ghosh, Jyotirmay Dwivedi, Emma Steinebronn, Anthony Richardella, K. Andre Mkhoyan, Nitin Samarth

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

Original languageEnglish (US)
Article number054004
JournalPhysical Review Applied
Issue number5
StatePublished - Nov 2022

Bibliographical note

Funding Information:
The authors would like to thank D.C. Ralph for valuable comments and A. Sengupta for providing access to apparatus used in ST FMR measurements. The principal support for this project is provided by SMART, one of seven centers of nCORE, a Semiconductor Research Corporation program, sponsored by the National Institute of Standards and Technology (NIST). This supported the synthesis and standard characterization of heterostructures as well as charge-spin conversion measurements (W.Y., Y.O., J.D., N.S.) and their characterization using STEM (S.G., A.M.). Additional support for materials synthesis and characterization was provided by the Penn State Two-Dimensional Crystal Consortium-Materials Innovation Platform (2DCC-MIP) under NSF Grant No. DMR-2039351 (R.X., E.S., A.R., N.S.). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award No. DMR-2011401) and the NNCI (Award No. ECCS-2025124) programs.

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© 2022 American Physical Society.

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