Chiral Symmetry and Spin Dynamics

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 6478

Special Issue Editor

Department of Physics, Shanghai University, Shanghai 200444, China
Interests: spintronics; micromagnetism; magnetization dynamics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Chirality is an old yet fundamental concept in Nature, manifesting in many disciplines, such as physics, chemistry and biology. Spin dynamics, usually referring to physical processes involving the spin reorientation or excitation of electrons, plays an essential role in emerging spintronics aiming at the manipulation of electron spins in magnetic nanostructures. Recent studies, both theoretical and experimental, have revealed intriguing phenomena that break the chiral symmetry in magnetization dynamics. Such effects include the asymmetric motion of magnetic domain walls (DWs), nonreciprocal propagation of spin waves (SWs) and closely associated so-called magnonic activity—a direct analogy to the famous effect of optical activity in optics. There are different physical origins responsible for these dynamic chiral effects. For instance, in magnetic systems involving the Dzyaloshinskii–Moriya interaction (DMI, an intrinsic asymmetric exchange interaction), chirality in dynamics emerges as a natural consequence. Extrinsically, a spin-polarized electric current passing through a magnetic medium can cause the SW nonreciprocality—the so-called current-induced SW Doppler shift—via the spin-transfer torque (STT) effect. Equally interestingly, chiral symmetry breaking in spin dynamics can be a purely geometric effect, arising from, for example, the curvilinear shape of magnetic nanocylinders. From an application perspective, chirality in spin dynamics provides a new dimension when designing future spintronic devices.

This Special Issue of Symmetry features articles about chiral symmetry in ferromagnetic or antiferromagnetic systems, covering a broad range of topics including: DM dynamics, SWs, DMI, STT, curvature magnetism, and the fabrication and characterization of curved magnetic structures.

Prof. Dr. Ming Yan
Guest Editor

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Keywords

  • chiral symmetry breaking
  • domain wall dynamics
  • spin waves
  • 3D magnetic structures
  • curved magnetic structures
  • spintronic devices
  • spin-transfer torque (STT)
  • Dzyaloshinskii-Moriya interaction (DMI)
  • antiferromagnetic system

Published Papers (5 papers)

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Research

9 pages, 2676 KiB  
Article
High Circular Dichroism Optical Chiral Metasurfaces Based on Bound States in the Continuum
Symmetry 2023, 15(7), 1444; https://doi.org/10.3390/sym15071444 - 19 Jul 2023
Cited by 1 | Viewed by 949
Abstract
In this paper, we suggest a design for a chiral metasurface at optical frequencies that shows a high level of circular dichroism (CD) of 0.94. By breaking the in-plane asymmetry and exciting the quasi-bound states in the continuum (quasi-BICs), a high Q-factor was [...] Read more.
In this paper, we suggest a design for a chiral metasurface at optical frequencies that shows a high level of circular dichroism (CD) of 0.94. By breaking the in-plane asymmetry and exciting the quasi-bound states in the continuum (quasi-BICs), a high Q-factor was obtained, which greatly enhances the interaction between light and matter. Then, the multipole decomposition was confirmed to analyze its mode of excitation. The proposed design may provide new possibilities for high-performance optical devices. Full article
(This article belongs to the Special Issue Chiral Symmetry and Spin Dynamics)
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13 pages, 600 KiB  
Article
Spin and Orbital Symmetry Breakings Central to the Laser-Induced Ultrafast Demagnetization of Transition Metals
Symmetry 2023, 15(2), 457; https://doi.org/10.3390/sym15020457 - 09 Feb 2023
Cited by 2 | Viewed by 989
Abstract
The role of spin and orbital rotational symmetry on the laser-induced magnetization dynamics of itinerant-electron ferromagnets was theoretically investigated. The ultrafast demagnetization of transition metals is shown to be the direct consequence of the fundamental breaking of these conservation laws in the electronic [...] Read more.
The role of spin and orbital rotational symmetry on the laser-induced magnetization dynamics of itinerant-electron ferromagnets was theoretically investigated. The ultrafast demagnetization of transition metals is shown to be the direct consequence of the fundamental breaking of these conservation laws in the electronic system, an effect that is inherent to the nature of spin-orbit and electron-lattice interactions. A comprehensive symmetry analysis is complemented by exact numerical calculations of the time evolution of optically excited ferromagnetic ground states in the framework of a many-body electronic Hamiltonian. Thus, quantitative relations are established between the strength of the interactions that break the rotational symmetries and the time scales that are relevant for the magnetization dynamics. Full article
(This article belongs to the Special Issue Chiral Symmetry and Spin Dynamics)
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18 pages, 2660 KiB  
Article
Chiral Magnetic Interactions in Small Fe Clusters Triggered by Symmetry-Breaking Adatoms
Symmetry 2023, 15(2), 397; https://doi.org/10.3390/sym15020397 - 02 Feb 2023
Viewed by 1368
Abstract
The chirality of the interaction between the local magnetic moments in small transition-metal alloy clusters is investigated in the framework of density-functional theory. The Dzyaloshinskii–Moriya (DM) coupling vectors Dij between the Fe atoms in Fe2X and Fe3X [...] Read more.
The chirality of the interaction between the local magnetic moments in small transition-metal alloy clusters is investigated in the framework of density-functional theory. The Dzyaloshinskii–Moriya (DM) coupling vectors Dij between the Fe atoms in Fe2X and Fe3X with X = Cu, Pd, Pt, and Ir are derived from independent ground-state energy calculations for different noncollinear orientations of the local magnetic moments. The local-environment dependence of Dij and the resulting relative stability of different chiral magnetic orders are analyzed by contrasting the results for different adatoms X and by systematically varying the distance between the adatom X and the Fe clusters. One observes that the adatoms trigger most significant DM couplings in Fe2X, often in the range of 10–30 meV. Thus, the consequences of breaking the inversion symmetry of the Fe dimer are quantified. Comparison between the symmetric and antisymmetric Fe-Fe couplings shows that the DM couplings are about two orders of magnitude weaker than the isotropic Heisenberg interactions. However, they are in general stronger than the anisotropy of the symmetric couplings. In Fe3X, alloying induces interesting changes in both the direction and strength of the DM couplings, which are the consequence of breaking the reflection symmetry of the Fe trimer and which depend significantly on the adatom-trimer distance. A local analysis of the chirality of the electronic energy shows that the DM interactions are dominated by the spin-orbit coupling at the adatoms and that the contribution of the Fe atoms is small but not negligible. Full article
(This article belongs to the Special Issue Chiral Symmetry and Spin Dynamics)
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13 pages, 11462 KiB  
Article
Influence of Physical Symmetries on the Magnetization Dynamics in Magnetic Fibers
Symmetry 2023, 15(1), 234; https://doi.org/10.3390/sym15010234 - 13 Jan 2023
Viewed by 1103
Abstract
Magnetic nanofibers belong to the geometries which are intensively investigated in simulations and experiments due to their unique magnetic properties, varying in their lengths, cross-sections, and bending radii. Besides basic research of different magnetization reversal processes and magnetization dynamics in bent nanofibers, these [...] Read more.
Magnetic nanofibers belong to the geometries which are intensively investigated in simulations and experiments due to their unique magnetic properties, varying in their lengths, cross-sections, and bending radii. Besides basic research of different magnetization reversal processes and magnetization dynamics in bent nanofibers, these structures are of potential interest for data storage applications, data transport, or other tasks in spintronics devices. While previous simulations concentrated on the domain wall transport through coupled bent nanofibers, creating networks with many in- and outputs to establish nanofiber-based domain wall logics, here we show the influence of the constricted area, in which a rotating magnetic field is applied in the middle of bent or straight magnetic nanofibers, on the magnetization dynamics. Our micromagnetic simulations, performed by Magpar, reveal a strong impact not only of this area, but also of the curvature of the nanofiber as well as of an additional Dzyaloshinskii–Moriya interaction (DMI). Full article
(This article belongs to the Special Issue Chiral Symmetry and Spin Dynamics)
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11 pages, 6259 KiB  
Article
Asymmetric Motion of Magnetic Skyrmions in Ferromagnetic Nanotubes Induced by a Magnetic Field
Symmetry 2022, 14(6), 1195; https://doi.org/10.3390/sym14061195 - 09 Jun 2022
Cited by 2 | Viewed by 1392
Abstract
Magnetic skyrmions, featuring topological stability and low driving current density, are believed to be a promising candidate of information carriers. One of the obstacles to application is the skyrmion Hall effect, which can lead to the annihilation of moving skyrmions at the lateral [...] Read more.
Magnetic skyrmions, featuring topological stability and low driving current density, are believed to be a promising candidate of information carriers. One of the obstacles to application is the skyrmion Hall effect, which can lead to the annihilation of moving skyrmions at the lateral boundary of thin-film tracks. In order to resolve this issue, it was recently proposed to exploit ferromagnetic nanotubes as alternative skyrmion guides. In this work, we investigate the field-effect of current-driven skyrmion motion in nanotubes using micromagnetic simulations. It is found that, in the presence of an axial field, the skyrmion motion becomes asymmetric in tubes. This is fundamentally different from the flat strip, in which a field has little influence on the skyrmion dynamics. Based on the dissipation tensor determined by the spin texture of the skyrmions, the solution of the Thiele equation is obtained, yielding a perfect match with simulations. We argue that the asymmetry of the skyrmion dynamics originates from the curvature of the nanotube. Full article
(This article belongs to the Special Issue Chiral Symmetry and Spin Dynamics)
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