Inhibition of Skyrmion Hall Effect by a Stripe Domain Wall

Sheng Yang, Kai Wu, Yuelei Zhao, Xue Liang, Jing Xia, Yuqing Zhou, Xiangjun Xing, and Yan Zhou

Phys. Rev. Applied 18, 024030 – Published 10 August 2022

Abstract

Magnetic skyrmions are topologically protected particlelike spin textures initially discovered in chiral magnetic materials. When driven by an electric current, magnetic skyrmions move at a certain angle (i.e., skyrmion Hall angle) with respect to the driving current due to the Magnus force, giving rise to the so-called skyrmion Hall effect (SHE). The SHE often leads to skyrmion annihilation at the sample edge, which is detrimental for practical applications. In this work, we study, experimentally and through micromagnetic simulations, the current-driven dynamics of skyrmion bubbles (SBs) in $Pt / Co / Ru$ multilayer stacks. It is observed that, under certain circumstances, a long stripe domain will form and align along the sample edge, which separates the skyrmion bubbles from the edge and avoids their annihilation at the edge. Furthermore, the velocity of the skyrmion bubbles can be increased by the stripe domain wall (DW) through the DW-SB interaction, as predicted in our early theory. Our results deepen our understanding of skyrmion dynamics and pave the way to the realization of highly efficient information processing and computing devices based on ultrafast skyrmion motion.

Received 27 December 2021
Revised 27 April 2022
Accepted 24 June 2022

DOI:https://doi.org/10.1103/PhysRevApplied.18.024030

Physics Subject Headings (PhySH)

Domain walls Magnetic domains Skyrmions Spin Hall effect Spintronics Stripes

Drops & bubbles Magnetic multilayers

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Sheng Yang ^1,‡, Kai Wu^1,‡, Yuelei Zhao^1,‡, Xue Liang¹, Jing Xia², Yuqing Zhou¹, Xiangjun Xing^3,*, and Yan Zhou ^1,†

¹School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen 518172, China
²College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, China
³School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China

^*xjxing@gdut.edu.cn
^†zhouyan@cuhk.edu.cn
^‡S. Yang, K. Wu, and Y. Zhao contributed equally to this work.

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Vol. 18, Iss. 2 — August 2022

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Images

Figure 1
Multilayer-stack magnetic thin film. (a) Optical hysteresis loop of the device with the $Ta (5) / [Pt (0.5) / Co (0.5)]_{3} / Ru (1.8) / [Co (0.5) / Pt (0.5)]_{3} / Ta (5)$ stack structure is measured by polar MOKE, showing a coercivity of about ±14 mT. Inset, cross section of the multilayer. (b) Evolution of magnetic domain patterns in out-of-plane external fields. Device is 20 µm in width and 120 µm in length. m_z is the z component of normalized magnetization. (c) Multiple 64-mA 28-µs sine pulses can generate stripe domains (see Video 1). (d) Single 65 mA with period of 28-µs sine pulse can generate skyrmion bubbles (see Video 2). (e) Creation of skyrmion bubbles by a single sine pulse with amplitude of 78 mA and period of 28 µs (see Video 3).
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Figure 2
Current-driven skyrmion motion. (a)–(g) Sequence of MOKE images of the skyrmion bubble (circled in yellow) driven by electron-current pulses. Pulse count is labeled at the top of each MOKE image. Pulse 1 is imposed right after the creation of skyrmion bubbles. Pulses 2–43 are sequential 84-mA (current density of 2.36 × 10¹¹ A/m²) 10-µs square-wave pulses. Electron current is along +x (see Video 9 for (a)–(d) and Video 10 for (e)–(g) [77]). Sample is positively saturated, and all the experiments are performed under an external field of µ₀H_z = 0.4 mT. (h) Skyrmion velocity as a function of pulse count. (i)–(k) Velocity increase contributed by the DW-SB interactions. Average velocity without the DW-SB interaction is shown for pulses 1–5, while the average velocity with the DW-SB interaction is shown for pulses 6–10. Here, 10-µs square-wave pulses are used [see Video 11 for (i), Video 12 for (j), and Video 13 (k)].
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Figure 3
oommf simulation results of skyrmion motion. (a) Skyrmion motion along a nanowire without inclusion of a stripe domain wall. (b) Skyrmion motion along a nanowire including a stripe domain wall. Electron current is along +x and current density is J = 10 MA/cm². Time elapsed from current onset is indicated at the top of each panel. Sample size is 1000 × 100 × 1 nm³ and the mesh size is 2 × 2 × 1 nm³.
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Figure 4
Stripe-domain formation and skyrmion-bubble depinning. (a)–(g) Escape process of a skyrmion bubble from a trapping potential. Square-wave-pulse amplitudes and durations are 86 mA (current density of 2.41 × 10¹¹ A/m²) and 10 µs, respectively. Electron current is along +x (see Video 15). (h),(i) Mechanism of stripe-domain formation. Under SOT, reverse domains 1 and 2 will merge when their caps contact, and reverse domain 3 will be split apart and vanish, leaving a stripe domain on the left edge.
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Figure 5
The 92-mA (3.28 × 10¹¹ A/m²) 5-µs square pulses can cause the deformation of skyrmion bubbles (see Video 16).
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