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Nagase T, So YG, Yasui H, Ishida T, Yoshida HK, Tanaka Y, Saitoh K, Ikarashi N, Kawaguchi Y, Kuwahara M, Nagao M. Observation of domain wall bimerons in chiral magnets. Nat Commun 2021; 12:3490. [PMID: 34108478 PMCID: PMC8190141 DOI: 10.1038/s41467-021-23845-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 05/19/2021] [Indexed: 12/03/2022] Open
Abstract
Topological defects embedded in or combined with domain walls have been proposed in various systems, some of which are referred to as domain wall skyrmions or domain wall bimerons. However, the experimental observation of such topological defects remains an ongoing challenge. Here, using Lorentz transmission electron microscopy, we report the experimental discovery of domain wall bimerons in chiral magnet Co-Zn-Mn(110) thin films. By applying a magnetic field, multidomain structures develop, and simultaneously, chained or isolated bimerons arise as the localized state between the domains with the opposite in-plane components of net magnetization. The multidomain formation is attributed to magnetic anisotropy and dipolar interaction, and domain wall bimerons are stabilized by the Dzyaloshinskii-Moriya interaction. In addition, micromagnetic simulations show that domain wall bimerons appear for a wide range of conditions in chiral magnets with cubic magnetic anisotropy. Our results promote further study in various fields of physics.
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Affiliation(s)
- Tomoki Nagase
- Department of Electronics, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
| | - Yeong-Gi So
- Department of Materials Science, Graduate School of Engineering Science, Akita University, Akita, Japan
| | - Hayata Yasui
- Department of Materials Science, Graduate School of Engineering Science, Akita University, Akita, Japan
| | - Takafumi Ishida
- Advanced Measurement Technology Center, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Hiroyuki K Yoshida
- Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Japan
| | - Yukio Tanaka
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Koh Saitoh
- Advanced Measurement Technology Center, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Nobuyuki Ikarashi
- Department of Electronics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
- Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan
| | - Yuki Kawaguchi
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Makoto Kuwahara
- Advanced Measurement Technology Center, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan.
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
| | - Masahiro Nagao
- Department of Electronics, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
- Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan.
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Lavrentovich OD. Design of nematic liquid crystals to control microscale dynamics. LIQUID CRYSTALS REVIEWS 2021; 8:59-129. [PMID: 34956738 PMCID: PMC8698256 DOI: 10.1080/21680396.2021.1919576] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Accepted: 04/11/2021] [Indexed: 05/25/2023]
Abstract
The dynamics of small particles, both living such as swimming bacteria and inanimate, such as colloidal spheres, has fascinated scientists for centuries. If one could learn how to control and streamline their chaotic motion, that would open technological opportunities in the transformation of stored or environmental energy into systematic motion, with applications in micro-robotics, transport of matter, guided morphogenesis. This review presents an approach to command microscale dynamics by replacing an isotropic medium with a liquid crystal. Orientational order and associated properties, such as elasticity, surface anchoring, and bulk anisotropy, enable new dynamic effects, ranging from the appearance and propagation of particle-like solitary waves to self-locomotion of an active droplet. By using photoalignment, the liquid crystal can be patterned into predesigned structures. In the presence of the electric field, these patterns enable the transport of solid and fluid particles through nonlinear electrokinetics rooted in anisotropy of conductivity and permittivity. Director patterns command the dynamics of swimming bacteria, guiding their trajectories, polarity of swimming, and distribution in space. This guidance is of a higher level of complexity than a simple following of the director by rod-like microorganisms. Namely, the director gradients mediate hydrodynamic interactions of bacteria to produce an active force and collective polar modes of swimming. The patterned director could also be engraved in a liquid crystal elastomer. When an elastomer coating is activated by heat or light, these patterns produce a deterministic surface topography. The director gradients define an activation force that shapes the elastomer in a manner similar to the active stresses triggering flows in active nematics. The patterned elastomer substrates could be used to define the orientation of cells in living tissues. The liquid-crystal guidance holds a major promise in achieving the goal of commanding microscale active flows.
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Affiliation(s)
- Oleg D Lavrentovich
- Advanced Materials and Liquid Crystal Institute, Department of Physics, Materials Science Graduate Program, Kent State University, Kent, OH 44242, USA
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Affiliation(s)
- Thomas Machon
- H.H. Wills Physics Laboratory, Tyndall Avenue, United Kingdom
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