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Crystallinity Control of the Topological-Insulator Surface Bi85Sb15(012) via Interfacial Engineering for Enhanced Spin-Orbit Torque

H. Y. Poh1,2, C. C. I. Ang1, G. J. Lim1, T. L. Jin1, S. H. Lee1,2, E. K. Koh1,2, F. Poh2, and W. S. Lew1,*

  • 1School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
  • 2GLOBALFOUNDRIES Singapore Pte. Ltd., 60 Woodlands Industrial Park D St 2, Singapore 738406, Singapore

  • *wensiang@ntu.edu.sg
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Phys. Rev. Applied 19, 034012 – Published 3 March, 2023

DOI: https://doi.org/10.1103/PhysRevApplied.19.034012

Abstract

Topological insulators demonstrate high charge-spin conversion efficiency due to their spin-momentum locking at the Dirac surface states. However, the surface states are sensitive to disruption caused by exchange coupling when interfaced with a ferromagnet. Here, we demonstrate the use of various nonmagnetic insertion layer materials, Ti,Cu, and Pt, at the Co/Bi-Sb(012) interface to preserve the topological surface state and promote spin-orbit-torque efficiency through the crystallinity control of Bi-Sb(012). For 20-nm-thick Bi-Sb, a spin Hall angle of up to 8.93 is observed with the use of a Pt insertion layer, while it is otherwise negligible for Co/Bi-Sb(012) interfaces. We further explore the enhancement of Bi-Sb(012) crystallinity with increasing Bi-Sb thickness, revealing a rapidly increasing spin-orbit-torque efficiency that gradually saturates above 30 nm. A clear correlation between spin-orbit-torque efficiency and Bi-Sb(012) crystalline size is identified using x-ray diffractometry, establishing the origin of the high spin-orbit efficiency to be the Bi-Sb(012) crystalline orientation. Our work demonstrates the spin-orbit-torque origin in Bi-Sb experimentally and paves the way for the adaptation of topological insulators as a class of low-energy spin source material for spintronics applications.

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Phys. Rev. Applied 19, 034012– Published 3 March, 2023
  • Received 22 November 2022
  • Revised 27 January 2023
  • Accepted 6 February 2023
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