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Twisted Magnon as a Magnetic Tweezer

Yuanyuan Jiang, H. Y. Yuan, Z.-X. Li, Zhenyu Wang, H. W. Zhang, Yunshan Cao, and Peng Yan
Phys. Rev. Lett. 124, 217204 – Published 26 May 2020
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    Abstract

    Wave fields with spiral phase dislocations carrying orbital angular momentum (OAM) have been realized in many branches of physics, such as for photons, sound waves, electron beams, and neutrons. However, the OAM states of magnons (spin waves)—the building block of modern magnetism—and particularly their implications have yet to be addressed. Here, we theoretically investigate the twisted spin-wave generation and propagation in magnetic nanocylinders. The OAM nature of magnons is uncovered by showing that the spin-wave eigenmode is also the eigenstate of the OAM operator in the confined geometry. Inspired by optical tweezers, we predict an exotic “magnetic tweezer” effect by showing skyrmion gyrations under twisted magnons in the exchange-coupled nanocylinder-nanodisk heterostructure, as a practical demonstration of magnonic OAM transfer to manipulate topological spin defects. Our study paves the way for the emerging magnetic manipulations by harnessing the OAM degree of freedom of magnons.

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    • Received 29 October 2019
    • Accepted 30 April 2020

    DOI:https://doi.org/10.1103/PhysRevLett.124.217204

    © 2020 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Magnetic textureMagnonsSkyrmions
    1. Properties
    Angular momentum
    1. Techniques
    Landau-Lifschitz-Gilbert equationMicromagnetic modeling
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Yuanyuan Jiang1, H. Y. Yuan2, Z.-X. Li1, Zhenyu Wang1, H. W. Zhang1, Yunshan Cao1, and Peng Yan1,*

    • 1School of Electronic Science and Engineering and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
    • 2Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China

    • *yan@uestc.edu.cn

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    Vol. 124, Iss. 21 — 29 May 2020

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    Images

    • Figure 1
      Figure 1

      Schematic illustration of a heterostructured nanocylinder exchange coupled to a chiral magnetic nanodisk hosting a Néel-type skyrmion. A static field H is applied along the z direction. A spin-wave beam with the wave vector k and OAM quantum number ℓ=−5 is excited by a local microwave field B applied over the yellow-disk region, leading to a steady skyrmion gyration around the disk center.

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    • Figure 2
      Figure 2

      (a) Boundary-value determinant versus trial frequencies for a longitudinal wave vector k=1×105  cm−1 and ℓ=−5. (b) Spin-wave spectrum in the nanocylinder. Solid curves are theoretical results, comparing with the FFT transform amplitude of mx from micromagnetic simulations. (c) Cross-sectional distribution of spin-wave beams with 0, 1, 2, and 3 radial nodes (from left to right) [46].

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    • Figure 3
      Figure 3

      (a) Cross-sectional view of spin-wave beams carrying different OAMs. (b) Time evolution of Néel skyrmions driven by twisted magnons with OAM ℓ=∓5. The time intervals between successive snapshots are 1.65 and 1.98 ns, respectively. A negative (positive) OAM induces a clockwise (counterclockwise) skyrmion gyration.

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    • Figure 4
      Figure 4

      (a) Skyrmion gyration path (symbols) and the circle fitting (red circle) for ℓ=−5. The gray curve represents the path for ℓ=0. (b) Time dependence of Ux (blue line) and Uy (red line). The inset shows the high-frequency details of the FFT spectrum (left) and Ux (right). Skyrmion velocity and orbit radius as a function of (c) damping parameter α′ and (d) OAM quantum number ℓ. The inset plots the U dependence of K and λ.

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