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The strong spin-orbit torque (SOT) generated by topological insulators (TIs) interfaced with ferromagnetic layers paves the path towards high-performance and low-power spintronic device applications. To date, large spin-to-charge or charge-to-spin conversion efficiency (ξ) of TIs is accomplished on high-quality epitaxially grown TI thin films on specifically oriented substrates. Moreover, the emergence of topological surface states (TSS) largely depends on the composition, which is hard to obtain on a large scale using sputtering growth. Here, we report a room-temperature ξ of BiSb/Py bilayer thin films with Titanium insertion (Ti) grown on Si substrates, which underlines the potential of BiSb for industrial applications and its adaptability to industrial-friendly processes. In this work, spin pumping and inverse spin Hall effect (ISHE) studies are performed on magnetron-sputtered BiSb(x)/Ti(x)/Py(10 nm) stacks by varying the thicknesses of BiSb and Ti insertion. The ξ has improved from 8 nm to 12 nm of BiSb in BiSb(x)/Ti(3 nm)/Py(10 nm) samples, and we found ξ of 3.71 in the BiSb(12 nm)/Ti(3 nm)/Py(10 nm) sample. This increasing trend in ξ with the thickness of BiSb is also consistently observed in spin-torque ferromagnetic resonance (ST-FMR) measurements. However, a decreasing trend in ξ was noted with the insertion layer thickness increased to 4 and 8 nm, underscoring the critical role of spacer layer thickness in determining ξ. Our results demonstrate the process involved in depositing a homogeneous BiSb layer directly on the Si substrate and the impact of the thickness of the insertion layer and BiSb on the ξ in topological material/ferromagnet bilayer systems. The relatively high ξ in TI grown on Si substrate paves the way for the development of low-power, high-speed CMOS-compatible novel spin-orbit torque devices.

Rights:

• Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International
  

Keyword: Spin-charge interconversion, Polycrystalline BiSb, Thickness dependence

Date published: 2025-08-07

Publisher: AIP Publishing

Journal:

• Journal of Applied Physics (ISSN: 00218979) vol. 138 issue. 5 053903

Funding:

• JICA Friendship AC2023-7

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5745

First published URL: https://doi.org/10.1063/5.0280905

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Updated at: 2025-09-10 16:30:20 +0900

Published on MDR: 2025-09-10 16:19:36 +0900