Emergence of skyrmion lattices and bimerons in chiral magnetic thin films with nonmagnetic impurities

Silva, R.L.; Secchin, Leonardo D.; Moura-Melo, W. A.; Pereira, A. R.; Stamps, R. L.

doi:10.1103/physrevb.89.054434

Cited by 49 publications

(29 citation statements)

References 33 publications

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“…Any application involving the movement of skyrmions, such as skyrmion-based racetrack memories, will profit from the fact that extremely low spin-polarized currents are sufficient to drive skyrmions, as shown by numerical simulations 26,78 . However, it remains to be further experimentally investigated which type of defects may pin skyrmions in ultrathin films and multilayers [79][80][81][82] , leading to a modified behaviour compared to that predicted by theoretical models, which are usually based on ideal metal layer structures. In this respect, the comparison of experimental results obtained for epitaxially grown and sputter-deposited thin magnetic films and multilayer structures, as well as between polycrystalline and amorphous layers, can be very valuable-it can provide a deeper insight into the role of structural imperfections and spatial inhomogeneities of the relevant magnetic material parameters for the static properties and dynamic behaviour of nanoscale magnetic skyrmions.…”

Section: Towards Skyrmion-based Devicesmentioning

confidence: 99%

Nanoscale magnetic skyrmions in metallic films and multilayers: a new twist for spintronics

2016

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Magnetic skyrmions are chiral quasiparticles that show promise for the transportation and storage of information. On a fundamental level, skyrmions are model systems for topologically protected spin textures and can be considered as the counterpart of topologically protected electronic states, emphasizing the role of topology in the classification of complex states of condensed matter. Recent impressive demonstrations of control of individual nanometer-scale skyrmionsincluding their creation, detection, manipulation and deletion-have raised expectations for their use in future spintronic devices, including magnetic memories and logic gates. From a materials perspective, it is remarkable that skyrmions can be stabilized in ultrathin transition metal films, such as Fe-one of the most abundant elements on earth-if these are in contact with materials that exhibit high spin-orbit coupling. At present, research in this field is focused on the development of transition-metal-based magnetic multilayer structures that support skyrmionic states at room temperature and allow for precise control of skyrmions by spin-polarized currents and external fields.

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Section: Towards Skyrmion-based Devicesmentioning

confidence: 99%

Nanoscale magnetic skyrmions in metallic films and multilayers: a new twist for spintronics

2016

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“…Since this initial discovery there has been tremendous growth in the field as an increasing number of materials have been found that can support a skyrmion phase [3][4][5][6][7][8][9][10] . There are also numerous proposals on how to stabilize skyrmion states by utilizing different materials properties or bilayers [11][12][13][14] . Direct imaging of skyrmions with Lorentz microscopy [3][4][5]7,10 and other techniques 8,15,16 show that the skyrmions form a triangular lattice and have particle-like properties similar to vortices in type-II superconductors 17 .…”

Section: Introductionmentioning

confidence: 99%

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

2015

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We examine the dynamics of a skyrmion moving over a two-dimensional periodic substrate utilizing simulations of a particle-based skyrmion model. We specifically examine the role of the non-dissipative Magnus term on the driven motion and the resulting skyrmion velocity-force curves. In the overdamped limit, there is a depinning transition into a sliding state in which the skyrmion moves in the same direction as the external drive. When there is a finite Magnus component in the equation of motion, a skyrmion in the absence of a substrate moves at an angle with respect to the direction of the external driving force. When a periodic substrate is added, the direction of motion or Hall angle of the skyrmion is dependent on the amplitude of the external drive, only approaching the substrate-free limit for higher drives. Due to the underlying symmetry of the substrate the direction of skyrmion motion does not change continuously as a function of drive, but rather forms a series of discrete steps corresponding to integer or rational ratios of the velocity components perpendicular ( V ⊥ ) and parallel ( V || ) to the external drive direction: V ⊥ / V || = n/m, where n and m are integers. The skyrmion passes through a series of directional locking phases in which the motion is locked to certain symmetry directions of the substrate for fixed intervals of the drive amplitude. Within a given directionally locked phase, the Hall angle remains constant and the skyrmion moves in an orderly fashion through the sample. Signatures of the transitions into and out of these locked phases take the form of pronounced cusps in the skyrmion velocity versus force curves, as well as regions of negative differential mobility in which the net skyrmion velocity decreases with increasing external driving force. The number of steps in the transport curve increases when the relative strength of the Magnus term is increased. We also observe an overshoot phenomena in the directional locking, where the skyrmion motion can lock to a Hall angle greater than the clean limit value and then jump back to the lower value at higher drives. The skyrmion-substrate interactions can also produce a skyrmion acceleration effect in which, due to the non-dissipative dynamics, the skyrmion velocity exceeds the value expected to be produced by the external drive. We find that these effects are robust for different types of periodic substrates. Using a simple model for a skyrmion interacting with a single pinning site, we can capture the behavior of the change in the Hall angle with increasing external drive. When the skyrmion moves through the pinning site, its trajectory exhibits a side step phenomenon since the Magnus term induces a curvature in the skyrmion orbit. As the drive increases, this curvature is reduced and the side step effect is also reduced. Increasing the strength of the Magnus term reduces the range of impact parameters over which the skyrmion can be captured by a pinning site, which is one of the reasons that strong Magnus force effects reduce the...

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“…Various stripes, including curved, ramified, maze, have long been observed in experiments and simulations [27][28][29][30][31][32][33][34], but there is no good description about those complex spin structures to date. For short race-track-like stripes, a notion of meron with ½ skyrmion number or bimeron [34][35][36] were used to describe one end or whole structure. This local description is not accurate and not necessary, an those bimerons should be correctly called skyrmions in order to reflect a holistic view of the spin structure.…”

Section: Discussionmentioning

confidence: 99%

Skyrmion crystal formation and magnetic field

Hu¹,

Wu²,

Wang³

2021

Preprint

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The roles of magnetic field and temperature in thermodynamic formation of skyrmion crystals (SkXs) have not been well-revealed to date. Here we present a unified theory about SkX formation and its fascinating thermodynamic behaviours. A chiral film can have many metastable states with an arbitrary number of skyrmions up to a maximal value. A perpendicular magnetic field makes a film with Qm skyrmions the lowest energy state. Qm first increases with the magnetic field up to an optimal value and then decreases with the field. The film with the largest Qm at the optimal field is an SkX. Outside of a field window, states consisting of various stripes with low skyrmion number densities are thermal equilibrium phases while an SkX is metastable. Within the field window, SkXs are the thermal equilibrium states below the Curie temperature. However, the time to reach an SkX state from a stripy phase would be too long at a low temperature. This causes a widely spread false belief that SkXs are metastable and stripy states are thermal equilibrium phase at low temperature and at the optimal field. Our theory opens a new avenue for SkX manipulation and skyrmion-based applications.

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Emergence of skyrmion lattices and bimerons in chiral magnetic thin films with nonmagnetic impurities

Cited by 49 publications

References 33 publications

Nanoscale magnetic skyrmions in metallic films and multilayers: a new twist for spintronics

Nanoscale magnetic skyrmions in metallic films and multilayers: a new twist for spintronics

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

Skyrmion crystal formation and magnetic field

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