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While compositional gradient-induced spin-current generation is explored, its microscopic mechanisms remain poorly understood. Here, the contribution of polarity of compositional gradient on spin-current generation is explored. A nanoscale compositional gradient, formed by in situ atomic diffusion of ultrathin Ti and W layers, is introduced between 10-nm-thick W and Ti layers. Spin-torque ferromagnetic resonance in ferromagnetic Ni95Cu5 deposited on this gradient reveals that a moderate compositional gradient suppresses negative spin torque from the spin Hall effect in W. In contrast, reversing the Ti/W stacking order, which inverts the gradient, suppresses positive spin torque from the orbital Hall effect in Ti. These findings suggest that the sign of spin torque is governed by the polarity of compositional gradient, providing a novel strategy for efficient spin-torque generation without relying on materials with strong spin or orbital Hall effect.

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• Creative Commons BY Attribution 4.0 International
  

Keyword: spintronics, spin vorticity coupling, spin torque, compositional gradient, transmission electron microscopy

Date published: 2025-04-08

Publisher: Wiley

Journal:

• Advanced Electronic Materials (ISSN: 2199160X)

Funding:

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5479

First published URL: https://doi.org/10.1002/aelm.202400797

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Updated at: 2025-05-16 09:20:20 +0900

Published on MDR: 2025-05-16 12:19:03 +0900