Nonlinear transport, dynamic ordering, and clustering for driven skyrmions on random pinning

Reichhardt, C.

doi:10.1103/physrevb.99.104418

Cited by 22 publications

(16 citation statements)

References 103 publications

(190 reference statements)

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“…For clarity, we have normalized V ⊥ to the value of V || at high drives by dividing V ⊥ by α m /α d and multiplying it by −1. We can also characterize the dynamic phases by measuring the skyrmion velocity deviations in the x and y-directions as in previous work 100,101 Fig. 14(b) indicates that the velocity deviations are largest in the plastic flow phase, and diminish to a constant value in the moving crystal phase.…”

Section: B Intermediate and High Magnus Forcementioning

confidence: 89%

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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Section: B Intermediate and High Magnus Forcementioning

confidence: 89%

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

Reichhardt

2020

Phys. Rev. B

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“…All particleparticle interactions have the same pairwise form of a modified Bessel function, F ss i = N i K 1 (r ij )r ij that falls off exponentially for large r. Here r ij = |r i −r j | is the distance between particles i and j, andr ij = (r i − r j )/r ij . This interaction potential has been used previously for particle-based models of skyrmions, and in the absence of pinning it causes the particles to form a hexagonal lattice 37,41,51,54,60 . The driving force F D = F Dx is the same for all particles.…”

Section: Simulationmentioning

confidence: 99%

“…In addition, clustering or species segregation can occur. Recent continuum and particle-based simulations of monodisperse skyrmions showed that clustering transitions can occur in samples containing strong pinning or quenched disorder 52,54 . Our results demonstrate that clustering can also occur in the absence of pinning when there is any dispersity in the skyrmions that produces differences in the Magnus term.…”

Section: Introductionmentioning

confidence: 99%

Disordering, clustering, and laning transitions in particle systems with dispersion in the Magnus term

Reichhardt

2019

Phys. Rev. E

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We numerically examine a two-dimensional system of repulsively interacting particles with dynamics that are governed by both a damping term and a Magnus term. The magnitude of the Magnus term has one value for half of the particles and a different value for the other half of the particles. In the absence of a driving force, the particles form a triangular lattice, while when a driving force is applied, we find that there is a critical drive above which a Magnus-induced disordering transition can occur even if the difference in the Magnus term between the two particle species is as small as one percent. The transition arises due to the different Hall angles of the two species, which causes their motion to decouple at the critical drive. At higher drives, the disordered state can undergo both species and density phase separation into a density modulated stripe that is oriented perpendicular to the driving direction. We observe several additional phases that occur as a function of drive and Magnus force disparity, including a variety of density modulated diagonal laned phases. In general we find a much richer variety of states compared to systems of oppositely driven overdamped Yukawa particles. We discuss the implications of our work for skyrmion systems, where we predict that even for small skyrmion dispersities, a drive-induced disordering transition can occur along with clustering phases and pattern forming states.

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“…Skyrmions moving near the boundary of a magnetic multilayer have also been shown to repel away from the boundary [27]. Furthermore, skyrmions interacting with neighbouring skyrmions have also been shown to repel each other due to the dipole-dipole and exchange interactions, thus leading to the possibility of skyrmionskyrmion interaction [28,29] and confinement of skyrmion diameter when a layer is saturated by skyrmions [30]; the extreme case being a skyrmion crystal. Driving individual skyrmions through a disordered landscape has been extensively studied under the effects of SOT from a HM layer [5,31], spin transfer torque (STT) in the FM layer [32], and more recently ISTT [24,25].…”

Section: Introductionmentioning

confidence: 99%

Collective skyrmion motion under the influence of an additional interfacial spin-transfer torque

MacKinnon¹,

Zeissler

Finizio

et al. 2022

Preprint

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Here we study the effect of an additional interfacial spin-transfer torque, as well as the well-established spin-orbit torque and bulk spin-transfer torque, on skyrmion collections – group of skyrmions dense enough that they are not isolated from one another – in ultrathin heavy metal / ferromagnetic multilayers, by comparing modelling with experimental results. Using a skyrmion collection with a range of skyrmion diameters and landscape disorder, we study the dependence of the skyrmion Hall angle on diameter and velocity, as well as the velocity as a function of diameter. We show that inclusion of the interfacial spin-transfer torque results in reduced skyrmion Hall angles, with values close to experimental results. We also show that for skyrmion collections the velocity is approximately independent of diameter, in marked contrast to the motion of isolated skyrmions, as the group of skyrmions move together at an average group velocity. Moreover, the calculated skyrmion velocities are comparable to those obtained in experiments when the interfacial spin-transfer torque is included. Our results thus show the significance of the interfacial spin-transfer torque in ultrathin magnetic multilayers, which helps to explain the low skyrmion Hall angles and velocities observed in experiment. We conclude that the interfacial spin-transfer torque should be considered in numerical modelling for reproduction of experimental results.

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Nonlinear transport, dynamic ordering, and clustering for driven skyrmions on random pinning

Cited by 22 publications

References 103 publications

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

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

Disordering, clustering, and laning transitions in particle systems with dispersion in the Magnus term

Collective skyrmion motion under the influence of an additional interfacial spin-transfer torque

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