• Open Access

Direct X-Ray Detection of the Spin Hall Effect in CuBi

Sandra Ruiz-Gómez, Rubén Guerrero, Muhammad W. Khaliq, Claudia Fernández-González, Jordi Prat, Andrés Valera, Simone Finizio, Paolo Perna, Julio Camarero, Lucas Pérez, Lucía Aballe, and Michael Foerster
Phys. Rev. X 12, 031032 – Published 1 September 2022

Abstract

The spin Hall effect and the inverse spin Hall effect are important spin-charge conversion mechanisms. The direct spin Hall effect induces a surface spin accumulation from a transverse charge current due to spin-orbit coupling even in nonmagnetic conductors. However, most detection schemes involve additional interfaces, leading to large scattering in reported data. Here we perform interface-free x-ray spectroscopy measurements at the Cu L3,2 absorption edges of highly Bi-doped Cu (Cu95Bi5). The detected x-ray magnetic circular dichroism signal corresponds to an induced magnetic moment of (2.2±0.5)×1012μBA1cm2 per Cu atom averaged over the probing depth, which is of the same order of magnitude as found for Pt measured by magneto-optics. The results highlight the importance of interface-free measurements to assess material parameters and the potential of CuBi for spin-charge conversion applications.

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  • Received 5 July 2021
  • Revised 11 February 2022
  • Accepted 12 July 2022

DOI:https://doi.org/10.1103/PhysRevX.12.031032

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Sandra Ruiz-Gómez1,2,*, Rubén Guerrero3, Muhammad W. Khaliq2, Claudia Fernández-González1,3, Jordi Prat2, Andrés Valera3, Simone Finizio4, Paolo Perna3, Julio Camarero3,5, Lucas Pérez1,3,6, Lucía Aballe2, and Michael Foerster2

  • 1Departamento de Física de Materiales, Universidad Complutense de Madrid, Plaza de las Ciencias 1, 28040 Madrid, Spain
  • 2ALBA Synchrotron Light Facility, CELLS, Carrer de la Llum, 2-26, E-08290 Bellaterra, Spain
  • 3Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
  • 4Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
  • 5Departamento de Física de la Materia Condensada e Instituto “Nicolás Cabrera” and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid (UAM), Campus de Cantoblanco. Madrid 28049, Spain
  • 6Surface Science and Magnetism of Low Dimensional Systems, UCM, Unidad Asociada al CSIC (IQFR), 28040 Madrid, Spain

  • *Present address: Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany.

Popular Summary

Electrons carry small magnetic moments called spins, which are usually balanced in the absence of magnetism. But when an electrical current flows through a material, a spin imbalance can be produced as a result of spin-orbit coupling. This “spin Hall effect” is a promising method for the manipulation of magnetic textures such as domain walls in multilayer materials, which can be key for future energy-efficient memory and computing devices. However, most measurement methods probe the combined properties of those multilayers, mixing material and interface properties. In this work, we present a direct probe of the spin imbalance due to the spin Hall effect in a single layer of a copper bismuth alloy.

We use a dedicated electron microscope to detect electrons emitted from the upper surface of the electrode structure when the sample is illuminated by synchrotron light (x rays). The absorption of the circularly polarized x rays is sensitive to electron spins inside the sample at particular photon energies. This effect is the most direct and element-sensitive probe of the spin imbalance and can be linked to the induced magnetic moment. The microscope allows us to focus on very small electrodes and compare neighboring areas with opposite current direction, boosting the experimental sensitivity. Moreover, the probing depth of about 5 nm allows us to probe only the upper surface of the sample, which is key, as otherwise, the signals from the upper and lower surface would cancel out.

This novel approach can be extended to other materials and constitutes the first element-specific detection method of the spin Hall effect.

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Vol. 12, Iss. 3 — July - September 2022

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