Manipulation of skyrmion motion by magnetic field gradients

Zhang, S. L.; Wang, Weiwei; Burn, D. M.; Peng, H-X; Berger, H.; Bauer, Andreas; Pfleiderer, C.; Laan, G. van der; Hesjedal, T.

doi:10.1038/s41467-018-04563-4

Cited by 129 publications

(90 citation statements)

References 44 publications

(74 reference statements)

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“…Magnetic skyrmions (skyrmions hereafter) have recently been the subject of great interest due both to their emerging physical effects and potential for applications [1,2]. Skyrmionic devices promise exceptional electrical efficiency -skyrmions can be directly driven by ultra-low current densities, and even controlled in the absence of current by static magnetic field gradients [3,4]. Their small size and unusual dynamics allow for their utilization in conventional computers, which has prompted a wide study of skyrmionic re-implementations of arithmetic logic units and memory storage devices [5,6].…”

Section: Introductionmentioning

confidence: 99%

Magnetic skyrmion interactions in the micromagnetic framework

2020

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Magnetic skyrmions are localized swirls of magnetization with a non-trivial topological winding number. This winding increases their robustness to superparamagnetism and gives rise to a myriad of novel dynamical properties, making them attractive as next-generation information carriers. Recently the equation of motion for a skyrmion was derived using the approach pioneered by Thiele, allowing for macroscopic skyrmion systems to be modeled efficiently. This powerful technique suffers from the prerequisite that one must have a priori knowledge of the functional form of the interaction between a skyrmion and all other magnetic structures in its environment. Here we attempt to alleviate this problem by providing a simple analytic expression which can generate arbitrary repulsive interaction potentials from the micromagnetic Hamiltonian. We also discuss a toy model of the radial profile of a skyrmion which is accurate for a wide range of material parameters.

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Section: Introductionmentioning

confidence: 99%

Magnetic skyrmion interactions in the micromagnetic framework

2020

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“…Another interesting effect is that shear banding could arise for driving either parallel or perpendicular to the inhomogeneous pinning regions due to the Magnus force. There have been some studies of skyrmions under inhomogeneous drives in the absence of pinning which produced evidence for rigid flow, disordered flow, and shear banding effects [76][77][78] .…”

Section: Introductionmentioning

confidence: 99%

Shear banding, intermittency, jamming, and dynamic phases for skyrmions in inhomogeneous pinning arrays

Reichhardt

2020

Phys. Rev. B

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We examine driven skyrmion dynamics in systems with inhomogeneous pinning where a strip of strong pinning coexists with a region containing no pinning. For driving parallel to the strip, we find that the initial skyrmion motion is confined to the unpinned region and the skyrmion Hall angle is zero. At larger drives, a transition occurs to a phase in which motion also appears within the pinned region, creating a shear band in the skyrmion velocity, while the skyrmion Hall angle is still zero. As the drive increases further, the flow becomes disordered and the skyrmion Hall angle increases with drive until saturating at the highest drives when the system transitions into a moving crystal phase. The different dynamic phases are associated with velocity and density gradients across the pinning boundaries. We map out the dynamic phases as a function of pinning strength, skyrmion density, and Magnus force strength, and correlate the phase boundaries with features in the velocity-force curves and changes in the local and global ordering of the skyrmion structure. For large Magnus forces, the shear banding instability is replaced by large scale intermittent flow in the pinned region accompanied by simultaneous motion perpendicular to the direction of the drive, which appears as oscillations in the transport curves. We also examine the case of a drive applied perpendicular to the strip, where we find a jamming effect in which the skyrmion flow is blocked by skyrmion-skyrmion interactions until the drive is large enough to induce plastic flow. arXiv:1911.06719v1 [cond-mat.mes-hall]

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“…Skyrmions are readily set into motion via the application of an external current [36,[39][40][41][42], and the resulting velocity-force relations show a pinned to sliding transition that can be observed in transport experiments by measuring changes in the topological Hall effect [39,43] or performing direct imaging of the skyrmion motion [37,40,44]. It is also possible to examine skyrmion dynamics using neutron scattering [45], x-ray diffraction [46], and changes in the noise fluctuations as a function of drive [47,48].Due to their stability, size scale, and manipulability, skyrmions are very promising candidates for a variety of applications including memory, logic devices, and alternative computing architectures [49,50]. The capability to precisely control the direction, traversal distance, and reversibility of skyrmion motion could open up new ways to create such devices, and there are already a number of proposals for controlling skyrmion motion using structured substrates such as race tracks [49,51,52], periodic modulations [53], or specially designed pinning structures [54][55][56][57][58].…”

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Skyrmion dynamics and topological sorting on periodic obstacle arrays

2020

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We examine skyrmions under a dc drive interacting with a square array of obstacles for varied obstacle size and damping. When the drive is applied in a fixed direction, we find that the skyrmions are initially guided in the drive direction but also move transverse to the drive due to the Magnus force. The skyrmion Hall angle, which indicates the difference between the skyrmion direction of motion and the drive direction, increases with drive in a series of quantized steps as a result of the locking of the skyrmion motion to specific symmetry directions of the obstacle array. On these steps, the skyrmions collide with an integer number of obstacles to create a periodic motion. The transitions between the different locking steps are associated with jumps or dips in the velocity-force curves. In some regimes, the skyrmion Hall angle is actually higher than the intrinsic skyrmion Hall angle that would appear in the absence of obstacles. In the limit of zero damping, the skyrmion Hall angle is 90 • , and we find that it decreases as the damping increases. For multiple interacting skyrmion species in the collective regime, we find jammed behavior at low drives where the different skyrmion species are strongly coupled and move in the same direction. As the drive increases, the species decouple and each can lock to a different symmetry direction of the obstacle lattice, making it possible to perform topological sorting in analogy to the particle sorting methods used to fractionate different species of colloidal particles moving over two-dimensional obstacle arrays. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische GesellschaftNew J. Phys. 22 (2020) 053025 N P Vizarim et alfrequency of the oscillations generated by the motion of the particle over the periodic substrate locks or comes into resonance with the ac drive frequency and its higher harmonics for a fixed range of drive intervals, producing steps in the velocity-force curves of the type found in Josephson junctions (which are known as Shapiro steps) [15,16], incommensurate sliding charge density waves [17], driven Frenkel-Kontorova systems [18], vortices in type-II superconductors moving over a periodic pinning substrate [19][20][21], and colloidal particles driven over periodic substrates [22,23]. In the case of the directional locking, there is no ac driving; however, two frequencies are still present, where one is associated with motion in the direction parallel to the drive and the other is associated with motion in the direction perpendicular to the drive. Directional locking can also arise in a system with a quasiperiodic substrate, where there are five or seven symmetry locking directions [24,25]. The locking can be harnessed for applications such as the sorting of different species of particles which have different sizes, charges, or damping, where a spatial separation of the species is achieved over time when one species locks to one angle while the other species locks to a different angl...

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Manipulation of skyrmion motion by magnetic field gradients

Cited by 129 publications

References 44 publications

Magnetic skyrmion interactions in the micromagnetic framework

Magnetic skyrmion interactions in the micromagnetic framework

Shear banding, intermittency, jamming, and dynamic phases for skyrmions in inhomogeneous pinning arrays

Skyrmion dynamics and topological sorting on periodic obstacle arrays

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