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Skyrmions in chiral magnets

Skyrmions are nanoscale particlelike magnetic textures discovered in chiral magnets in 2009. Since that time the field has shown tremendous growth, with the identification of more and more skyrmion-supporting materials and the development of additional experimental techniques capable of directly accessing the skyrmion dynamics. Skyrmions represent an example of a collectively interacting system of particles that can exhibit depinning and sliding phenomena, but unlike other such systems, due to the skyrmion topology a Magnus term plays a strong role in the skyrmion dynamics. Numerous recent theoretical and experimental papers have demonstrated that this Magnus term strongly affects the skyrmion motion and the interactions of the skyrmions with quenched disorder or pinning. We explore the rich dynamics that emerge in this novel system.

Preprints:

  1. Sliding dynamics of skyrmion molecular crystals
    J.C. Bellizotti Souza, C.J.O. Reichhardt, C. Reichhardt, N.P. Vizarim, and P.A. Venegas
    arXiv
    Using both atomistic and particle-based simulations, we investigate the current-driven dynamics of skyrmions on two-dimensional periodic substrates when there are multiple skyrmions per substrate minimum. At zero drive, the system forms pinned skyrmion molecular crystal states consisting of dimers, trimers, or dimer-trimer mixtures that have both positional and orientational order. On a square substrate lattice, the motion above depinning occurs via a running soliton that travels completely transverse to the applied current. This motion is generated by a torque from the Magnus force, which rotates the n-mer states perpendicular to the applied current. At higher drives, the flow becomes disordered while the Hall angle diminishes and gradually approaches the intrinsic value. In some cases, we also find directional locking where the Hall angle becomes locked to certain symmetry directions of the substrate over a range of currents. The transitions into and out of directionally locked states are accompanied by negative differential mobility in which the net velocity decreases as the drive increases. On a triangular substrate, we find no transverse mobility effects, but still observe directionally locked motion.


  2. Skyrmion-skyrmionium phase separation and laning transitions via spin-orbit torque currents
    N.P. Vizarim, J.C. Bellizotti Souza, C.J.O. Reichhardt, C. Reichhardt, P.A. Venegas, and F. Beron
    arXiv
    Many driven binary systems can exhibit laning transitions when the two species have different mobilities, such as colloidal particles with opposite charges in electric fields. Another example is pedestrian or active matter systems, where particles moving in opposite directions form a phase-separated state that enhances the overall mobility. In this work, we use atomistic simulations to demonstrate that mixtures of skyrmions and skyrmioniums also exhibit pattern formation and laning transitions. Skyrmions move more slowly and at a finite Hall angle compared to skyrmioniums, which move faster and without a Hall effect. At low drives, the system forms a partially jammed phase where the skyrmionium is dragged by the surrounding skyrmions, resulting in a finite angle of motion for the skyrmionium. At higher drives, the system transitions into a laned state, but unlike colloidal systems, the lanes in the skyrmion skyrmionium mixture are tilted relative to the driving direction due to the intrinsic skyrmion Hall angle. In the laned state, the skyrmionium angle of motion is reversed when it aligns with the tilted lane structure. At even higher drives, the skyrmioniums collapse into skyrmions. Below a critical skyrmion density, both textures can move independently with few collisions, but above this density, the laning state disappears entirely, and the system transitions to a skyrmion-only state. We map out the velocity and Hall responses of the different textures and identify three distinct phases: partially jammed, laned, and skyrmion-only moving crystal states. We compare our results to recent observations of tilted laning phases in pedestrian flows, where chiral symmetry breaking in the particle interactions leads to similar behavior.


  3. Topological transitions, pinning and ratchets for driven magnetic hopfions in nanostructures
    J.C. Bellizotti Souza, C.J.O. Reichhardt, C. Reichhardt, A. Saxena, N.P. Vizarim, and P.A. Venegas
    arXiv
    Using atomistic simulations, we examine the dynamics of three-dimensional magnetic hopfions interacting with an array of line defects or posts as a function of defect spacing, defect strength, and current. We find a pinned phase, a sliding phase where a hopfion can move through the posts or hurdles by distorting, and a regime where the hopfion becomes compressed and transforms into a toron that is half the size of the hopfion and moves at a lower velocity. The toron states occur when the defects are strong; however, in the toron regime, it is possible to stabilize sliding hopfions by increasing the applied current. Hopfions move without a Hall angle, while the toron moves with a finite Hall angle. We also show that when a hopfion interacts with an asymmetric array of planar defects, a ratchet effect consisting of a net dc motion can be realized under purely ac driving.


Papers:

  1. Skyrmionium dynamics and stability on one dimensional anisotropy patterns
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    J. Phys.: Condens. Matt., in press (2025). arXiv


  2. Comparing dynamics, pinning and ratchet effects for skyrmionium, skyrmions, and antiskyrmions
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    J. Phys.: Condens. Matt. 37, 165801 (2025). arXiv


  3. Skyrmion soliton motion on periodic substrates by atomistic and particle based simulations
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    EPL 148, 56002 (2024). arXiv


  4. Reversible to irreversible transitions for ac driven skyrmions on periodic substrates
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    New J. Phys. 26, 113007 (2024). arXiv


  5. Skyrmion molecular crystals and superlattices on triangular substrates
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, P.A. Venegas, and C. Reichhardt
    Phys. Rev. B 111, 054402 (2025). arXiv


  6. Shapiro steps and stability of skyrmions interacting with alternating anisotropy under the influence of ac and dc drives
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    Phys. Rev. B 110, 014406 (2024). arXiv


  7. Controlled skyrmion ratchet in linear protrusion defects
    F.S. Rocha, J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    Phys. Rev. B 109, 054407 (2024). arXiv


  8. Skyrmion transport and annihilation in funnel geometries
    F.S. Rocha, J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    J. Phys.: Condens. Matter 36, 115801 (2024). arXiv


  9. Soliton motion induced along ferromagnetic skyrmion chains in chiral thin nanotracks
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    J. Mag. Mag. Mater. 587, 171280 (2023). arXiv


  10. Kibble-Zurek scenario and coarsening across nonequilibrium phase transitions in driven vortices and skyrmions
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. Res. 5, 033221 (2023). arXiv


  11. Peak effect, melting, and transport in skyrmion crystals
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. B 108, 014428 (2023). arXiv


  12. Spontaneous skyrmion conformal lattice and transverse motion during dc and ac compression
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    New J. Phys. 25, 053020 (2023). arXiv


  13. Magnus induced diode effect for skyrmions in channels with periodic potentials
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    J. Phys.: Condens. Matter 51, 015804 (2022). arXiv


  14. Editorial: Generation, detection and manipulation of skyrmions in magnetic nanostructures
    H.Y. Yuan, X. Zhang, and C.J.O. Reichhardt
    Front. Phys. 10, 964975 (2022).


  15. Dynamic phases and reentrant Hall effect for vortices and skyrmions on periodic pinning arrays
    C.J.O. Reichhardt and C. Reichhardt
    Eur. Phys. J. B 95, 135 (2022). arXiv


  16. Clogging, diode and collective effects of skyrmions in funnel geometries
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    New J. Phys. 24, 103030 (2022). arXiv


  17. Statics and dynamics of skyrmions interacting with disorder and nanostructures
    C. Reichhardt, C.J.O. Reichhardt, and M.V. Milosevic
    Rev. Mod. Phys. 94, 035005 (2022). arXiv


  18. Commensuration effects on skyrmion Hall angle and drag for manipulation of skyrmions on two-dimensional periodic substrates
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. B 105, 214437 (2022). arXiv


  19. Soliton motion in skyrmion chains: Stabilization and guidance by nanoengineered pinning
    N.P. Vizarim, J.C. Bellizotti Souza, C.J.O. Reichhardt, C. Reichhardt, M.V. Milosevic, and P.A. Venegas
    Phys. Rev. B 105, 224409 (2022). arXiv


  20. Directed motion of liquid crystal skyrmions with oscillating fields
    A. Duzgun, C. Nisoli, C.J.O. Reichhardt, and C. Reichhardt
    New J. Phys. 24, 033033 (2022). arXiv


  21. Fluctuations and pinning for individually manipulated skyrmions
    C.J.O. Reichhardt and C. Reichhardt
    Front. Phys. 9, 767491 (2021). arXiv


  22. Visualizing the strongly reshaped skyrmion Hall effect in multilayer wire devices
    A.K.C. Tan, P. Ho, J. Lourembam, L. Huang, H.K. Tan, C.J.O. Reichhardt, C. Reichhardt, and A. Soumyanarayan
    Nature Commun. 12, 4252 (2021). arXiv


  23. Dynamics and nonmonotonic drag for individually driven skyrmions
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. B 104, 064441 (2021). arXiv


  24. Skyrmion ratchet in funnel geometries
    J.C. Bellizotti Souza, N.P. Vizarim, C.J.O. Reichhardt, C. Reichhardt, and P.A. Venegas
    Phys. Rev. B 104, 054434 (2021). arXiv


  25. Directional locking and the influence of obstacle density on skyrmion dynamics in triangular and honeycomb arrays
    N.P. Vizarim, J.C. Bellizotti Souza, C. Reichhardt, C.J.O. Reichhardt, and P.A. Venegas
    J. Phys.: Condens. Matter 33, 305801 (2021). arXiv


  26. Guided skyrmion motion along pinning array interfaces
    N.P. Vizarim, C. Reichhardt, P.A. Venegas, and C.J.O. Reichhardt
    J. Mag. Mag. Mater. 528, 167710 (2021). arXiv


  27. Skyrmion pinball and directed motion on obstacle arrays
    N.P. Vizarim, C.J.O. Reichhardt, P.A. Venegas, and C. Reichhardt
    J. Phys. Commun. 4, 085001 (2020). arXiv


  28. Shapiro steps and nonlinear skyrmion Hall angles for dc and ac driven skyrmions on a two dimensional periodic substrate
    N.P. Vizarim, C. Reichhardt, P.A. Venegas, and C.J.O. Reichhardt
    Phys. Rev. B 102, 104413 (2020). arXiv


  29. Skyrmion dynamics and transverse mobility: Skyrmion Hall angle reversal on 2D periodic substrates with dc and biharmonic ac drives
    N.P. Vizarim, C.J.O. Reichhardt, P.A. Venegas, and C. Reichhardt
    Eur. Phys. J. B 93, 112 (2020) arXiv


  30. Dynamics of Magnus dominated particle clusters, collisions, pinning and ratchets
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. E 101, 062602 (2020). arXiv


  31. Skyrmion dynamics and topological sorting on periodic obstacle arrays
    N.P. Vizarim, C. Reichhardt, C.J.O. Reichhardt, and P.A. Venegas
    New J. Phys. 22, 053025 (2020). arXiv


  32. Commensurate states and pattern switching via liquid crystal skyrmions trapped in a square lattice
    A. Duzgun, C. Nisoli, C.J.O. Reichhardt, and C. Reichhardt
    Soft Matter 16, 3338 (2020). arXiv


  33. Shear banding, intermittency, jamming and dynamic phases for skyrmions in inhomogeneous pinning arrays
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. B 101, 054423 (2020). arXiv


  34. Chiral edge currents for ac driven skyrmions in confined pinning geometries
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. B 100, 174414 (2019). arXiv


  35. Reentrant pinning, dynamic row reduction, and skyrmion accumulation for driven skyrmions in inhomogeneous pinning arrays
    C. Reichhardt and C.J.O. Reichhardt
    EPL 129, 21001 (2020). arXiv


  36. Nonlinear transport, dynamic ordering, and clustering for driven skyrmions on random pinning
    C. Reichhardt and C.J.O. Reichhardt
    Phys. Rev. B 99, 104418 (2019). arXiv


  37. Skyrmions in anisotropic magnetic fields: Strain and defect dynamics
    R. Brearton, M.W. Olszewski, S. Zhang, M.R. Eskildsen, C. Reichhardt, C.J.O. Reichhardt, G. van der Laan, and T. Hesjedal
    MRS Adv. 4, 643 (2019).


  38. Disordering, clustering, and laning transitions in particle systems with dispersion in the Magnus term
    C.J.O. Reichhardt and C. Reichhardt
    Phys. Rev. E 99, 012606 (2019). arXiv


  39. Reversible to irreversible transitions in periodically driven skyrmion systems
    B.L. Brown, C. Reichhardt, and C.J.O. Reichhardt
    New J. Phys. 21, 013001 (2019). arXiv


  40. Thermal creep and the skyrmion Hall angle in driven skyrmion crystals
    C. Reichhardt and C.J.O. Reichhardt
    J. Phys.: Condens. Matter 31, 07LT01 (2019). arXiv


  41. Nonequilibrium phases and segregation for skyrmions on periodic pinning arrays
    C. Reichhardt, D. Ray, and C.J.O. Reichhardt
    Phys. Rev. B 98, 134418 (2018). arXiv


  42. Avalanches and criticality in driven magnetic skyrmions
    S.A. Diaz, C. Reichhardt, D.P. Arovas, A. Saxena, and C.J.O. Reichhardt
    Phys. Rev. Lett. 120, 117203 (2018). arXiv


  43. Fluctuations and noise signatures of driven magnetic skyrmions
    S.A. Diaz, C.J.O. Reichhardt, D.P. Arovas, A. Saxena, and C. Reichhardt
    Phys. Rev. B 96, 085106 (2017). arXiv


  44. Reversible vector ratchets for skyrmion systems
     X. Ma, C.J. Olson Reichhardt, and C. Reichhardt
    Phys. Rev. B 95, 104401 (2017). arXiv


  45. Shapiro spikes and negative mobility for skyrmion motion on quasi-one-dimensional periodic substrates
    C. Reichhardt and C.J. Olson Reichhardt
    Phys. Rev. B 95, 014412 (2017). arXiv


  46. Noise fluctuations and drive dependence of the skyrmion Hall effect in disordered systems
     C. Reichhardt and C.J. Olson Reichhardt
    New J. Phys. 18, 095005 (2016). arXiv


  47. Emergent geometric frustration of artificial magnetic skyrmion crystals
     F. Ma, C. Reichhardt, W. Gan, C.J. Olson Reichhardt, and W.S. Lew
    Phys. Rev. B 94, 144405 (2016) arXiv


  48. Magnus-induced dynamics of driven skyrmions on a quasi-one-dimensional periodic substrate
     C. Reichhardt and C.J. Olson Reichhardt
    Phys. Rev. B 94, 094413 (2016). arXiv


  49. Shapiro steps for skyrmion motion on a washboard potential with longitudinal and transverse ac drives
     C. Reichhardt and C.J. Olson Reichhardt
    Phys. Rev. B 92, 224432 (2015). arXiv


  50. Magnus-induced ratchet effects for skyrmions interacting with asymmetric substrates
    C. Reichhardt, D. Ray, and C.J. Olson Reichhardt
    New J. Phys. 17, 073034 (2015). arXiv


  51. Quantized transport for a skyrmion moving on a two-dimensional periodic substrate
    C. Reichhardt, D. Ray, and C.J. Olson Reichhardt
    Phys. Rev. B 91, 104426 (2015). arXiv


  52. Collective transport properties of driven skyrmions with random disorder
    C. Reichhardt, D. Ray, and C.J. Olson Reichhardt
    Phys. Rev. Lett. 114, 217202 (2015). arXiv


  53. Comparing the dynamics of skyrmions and superconducting vortices
    C.J. Olson Reichhardt, S.Z. Lin, D. Ray, and C. Reichhardt
    Physica C 503, 52 (2014). arXiv

Last modified Jan 7, 2019