Defect modeling in skyrmionic ferromagnetic systems

Del-Valle, Núria; Castell-Queralt, Josep; González-Gómez, Leonardo; Navau, Carles

doi:10.1063/5.0072709

Cited by 17 publications

(18 citation statements)

References 102 publications

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“…Additionally, skyrmions could change shape when interacting with structures or with the drive. An interesting future direction would be to consider continuum-based models for skyrmions and the skyrmion-barrier interactions [35,58,59] where the shape of the skyrmion could change as it moves though the funnel constrictions. In the clogging phase, the skyrmions could also become compressed or change shape, and it would be interesting to explore whether such extra degrees of freedom would enhance or decrease the clogging effects.…”

Section: Discussionmentioning

confidence: 99%

Clogging, Diode and Collective Effects of Skyrmions in Funnel Geometries

Souza¹,

Vizarim²,

Reichhardt³

et al. 2022

Preprint

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Using a particle-based model, we examine the collective dynamics of skyrmions interacting with a funnel potential under dc driving as the skyrmion density and relative strength of the Magnus and damping terms are varied. For driving in the easy direction, we find that increasing the skyrmion density reduces the average skyrmion velocity due to jamming of skyrmions near the funnel opening, while the Magnus force causes skyrmions to accumulate on one side of the funnel array. For driving in the hard direction, there is a critical skyrmion density below which the skyrmions become trapped. Above this critical value, a clogging effect appears with multiple depinning and repinning states where the skyrmions can rearrange into different clogged configurations, while at higher drives, the velocity-force curves become continuous. When skyrmions pile up near the funnel opening, the effective size of the opening is reduced and the passage of other skyrmions is blocked by the repulsive skyrmion-skyrmion interactions. We observe a strong diode effect in which the critical depinning force is higher and the velocity response is smaller for hard direction driving. As the ratio of Magnus force to dissipative term is varied, the skyrmion velocity varies in a non-linear and non-monotonic way due to the pile up of skyrmions on one side of the funnels. At high Magnus forces, the clogging effect for hard direction driving is diminished.

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Section: Discussionmentioning

confidence: 99%

Clogging, Diode and Collective Effects of Skyrmions in Funnel Geometries

Souza¹,

Vizarim²,

Reichhardt³

et al. 2022

Preprint

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“…The nanoscale topological skyrmion is a quasiparticle in magnetic systems [3][4][5]. It can be driven into motion by external forces [6][7][8][9][10][11][12][13][14][15], and can also interact with the substrate and show different dynamic behaviors depending on the landscape of substrate [16,17]. For example, in principle a single isolated skyrmion driven by a current in the magnetic layer usually moves in a straight line [6][7][8][9][10][11][12][13][14][15] and shows the skyrmion Hall effect [18][19][20], when the magnetic layer has no pinning effect and the skyrmion is far away from the layer boundaries.…”

Section: Introductionmentioning

confidence: 99%

“…For example, in principle a single isolated skyrmion driven by a current in the magnetic layer usually moves in a straight line [6][7][8][9][10][11][12][13][14][15] and shows the skyrmion Hall effect [18][19][20], when the magnetic layer has no pinning effect and the skyrmion is far away from the layer boundaries. However, when a pinning landscape is presented in the magnetic layer, the isolated skyrmion may show certain extraordinary dynamic behaviors that are determined by both the pinning and driving forces [16,17,[21][22][23][24][25][26][27][28][29][30][31]. For example, an isolated skyrmion interacting with asymmetric substrates and ac currents may show Magnus-induced ratchet effects [25].…”

Section: Introductionmentioning

confidence: 99%

Particle-like skyrmions interacting with a funnel obstacle

2022

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The skyrmion-substrate interaction is an important issue to consider when studying particle-like skyrmions in nanostructures, which may strongly affect the skyrmion dynamics and lead to complex dynamic phenomena. Here, we report the current-driven dynamic behaviors of particle-like skyrmions interacting with the funnel obstacle in a ferromagnetic layer. We computationally demonstrate that a funnel obstacle with enhanced perpendicular magnetic anisotropy can be used to modify the dynamics of skyrmions due to the repulsive skyrmion-funnel interaction, which could generate several nontrivial effects, including the compression, clogging, annihilation, guided motion, and capturing of skyrmions. It is also found that the funnel obstacle can separate an incoming flow of skyrmions into two asymmetric flows. Moreover, we show that it is possible to capture skyrmions by the funnel obstacle in both static and dynamic ways. Our results are useful for understanding the skyrmion dynamics interacting with the substrate and could provide guidelines for the control of skyrmion flows in a transmission channel.

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“…Due to their size scale, mobility, and stability, skyrmions are promising candidates for a variety of applications [21][22][23][24] , many of which require the ability to control how the skyrmions move, how they interact with defects or nanostructures, and how to manipulate them on the individual level. The skyrmions also interact with quenched disorder in the system, giving rise to a pinning effect and establishing a threshold driving force that must be applied for the skyrmion to be set in motion [25][26][27][28][29][30][31] . The magnitude of this threshold depends on the properties of the disorder 25,[32][33][34] , collective interactions with other skyrmions 35 , and thermal effects [36][37][38] .…”

Section: Introductionmentioning

confidence: 99%

“…The intrinsic skyrmion Hall angle θ int sk is proportional to the ratio of the Magnus or gyrotropic term to the dissipative term of the skyrmion dynamics. Many proposed skyrmion appli-cations require the reduction or absence of the skyrmion Hall effect, so there have been numerous studies focused on understanding how to control the skyrmion Hall angle, such as by the use of nanostructures 25,31 . The magnitude of the skyrmion Hall effect is modified both by the pinning landscape and by the velocity of the skyrmions.…”

Section: Introductionmentioning

confidence: 99%

Commensuration Effects on Skyrmion Hall Angle and Drag for Manipulation of Skyrmions on Two-Dimensional Periodic Substrates

Reichhardt,

Reichhardt

2022

Preprint

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We examine the dynamics of an individually driven skyrmion moving through a background lattice of skyrmions coupled to a 2D periodic substrate as we vary the ratio of the number of skyrmions to the number of pinning sites across commensurate and incommensurate conditions. As the skyrmion density increases, the skyrmion Hall angle is nonmonotonic, dropping to low or zero values in commensurate states and rising to an enhanced value in incommensurate states. Under commensuration, the driven skyrmion is channeled by a symmetry direction of the pinning array and exhibits an increased velocity. At fillings for which the skyrmion Hall angle is zero, the velocity has a narrow band noise signature, while for incommensurate fillings, the skyrmion motion is disordered and the velocity noise is broad band. Under commensurate conditions, multi-step depinning transitions appear and the skyrmion Hall angle is zero at low drives but becomes finite at higher drives, while at incommensurate fillings there is only a single depinning transition. As the gyrotropic component of the skyrmion dynamics, called the Magnus force, increases, peaks in the velocity that appear in commensurate regimes cross over to dips, and new types of directional locking effects can arise in which the skyrmion travels along other symmetry directions of the background lattice. At large Magnus forces, and particularly at commensurate fillings, the driven skyrmion can experience a velocity boost in which the skyrmion moves faster than the applied drive due to the alignment of the Magnus-induced velocity with the driving direction. In some cases, an increase of the Magnus force can produce regimes of enhanced pinning when the skyrmion is forced to move along a non-symmetry direction of the periodic pinning array. This is in contrast to systems with random pinning, where increasing the Magnus force generally reduces the pinning effect. We demonstrate these dynamics for both square and triangular substrates, and map out the different regimes as a function of filling fraction, pinning force, and the strength of the Magnus force in a series of dynamic phase diagrams.

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Defect modeling in skyrmionic ferromagnetic systems

Cited by 17 publications

References 102 publications

Clogging, Diode and Collective Effects of Skyrmions in Funnel Geometries

Clogging, Diode and Collective Effects of Skyrmions in Funnel Geometries

Particle-like skyrmions interacting with a funnel obstacle

Commensuration Effects on Skyrmion Hall Angle and Drag for Manipulation of Skyrmions on Two-Dimensional Periodic Substrates

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