Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet

Kurumaji, Takashi; Nakajima, Tsuyoshi; Hirschberger, Max; Kikkawa, Akiko; Yamasaki, Y.; Sagayama, Hajime; Nakao, Hironori; Taguchi, Y.; Arima, Taka‐hisa; Tokura, Y.

doi:10.1126/science.aau0968

Cited by 604 publications

(500 citation statements)

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“…However, the dynamics of magnetic bimerons driven by different external forces as well as the static properties of different forms of bimerons still remain elusive, especially for the bimerons in frustrated magnetic systems. Some most recent studies have focused on the existence and manipulation of skyrmions in frustrated magnetic systems [48,[64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]. Therefore, it is also imperative to study bimerons in frustrated magnetic systems, of which the physical properties are essential for designing future bimeron-based device applications.…”

Section: Introductionmentioning

confidence: 99%

Static and dynamic properties of bimerons in a frustrated ferromagnetic monolayer

et al. 2020

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Magnetic bimeron is a topological counterpart of skyrmions in in-plane magnets, which can be used as spintronic information carrier. We report the static properties of bimerons with different topological structures in a frustrated ferromagnetic monolayer, where the bimeron structure is characterized by the vorticity Qv and helicity η. It is found that the bimeron energy increases with Qv, and the energy of an isolated bimeron with Qv = ±1 depends on η. We also report the dynamics of frustrated bimerons driven by the spin-orbit torques, which depend on the strength of the damping-like and field-like torques. We find that the isolated bimeron with Qv = ±1 can be driven into linear or elliptical motion when the spin polarization is perpendicular to the easy axis. We numerically reveal the damping dependence of the bimeron Hall angle driven by the damping-like torque. Besides, the isolated bimeron with Qv = ±1 can be driven into rotation by the damping-like torque when the spin polarization is parallel to the easy axis. The rotation frequency is proportional to the driving current density. In addition, we numerically demonstrate the possibility of creating a bimeron state with a higher or lower topological charge by the current-driven collision and merging of bimeron states with different Qv. Our results could be useful for understanding the bimeron physics in frustrated magnets.

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Section: Introductionmentioning

confidence: 99%

Static and dynamic properties of bimerons in a frustrated ferromagnetic monolayer

et al. 2020

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“…It typically consists of a hexagonal array of topologically protected magnetic vortex-like structures that appear in a variety of different materials, usually stabilized by a combination of symmetric exchange, the Dzyaloshinskii-Moriya interaction (DMI), crystal anisotropies, and thermal fluctuations [4]. Since their first discovery in the B20 metal MnSi [6], skyrmions have been found in similar noncentrosymmetric materials such as FeGe [7], Fe 1−x Co x Si [8], Cu 2 OSeO 3 [9], and others [10][11][12], and recently in some centrosymmetric materials where geometric magnetic frustration is thought to play a role [19,20]. They have also been seen in grown thin films and multilayers where interfacial DMI [13][14][15] or a combination of DMI, uniaxial anisotropy, and geometric confinement [16][17][18] help stabilize the skyrmions.…”

Section: Introductionmentioning

confidence: 99%

Stability and metastability of skyrmions in thin lamellae ofCu2OSeO3

Wilson

Birch

Štefančič

et al. 2020

Phys. Rev. Research

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We report small angle X-ray scattering (SAXS) measurements of the skyrmion lattice in two 200 nm thick Cu2OSeO3 lamellae aligned with the applied magnetic field parallel to the out of plane [110] or [100] crystallographic directions. Our measurements show that the equilibrium skyrmion phase in both samples is expanded significantly compared to bulk crystals, existing between approximately 30 and 50 K over a wide region of magnetic field. This skyrmion state is elliptically distorted at low fields for the [110] sample, and symmetric for the [100] sample, possibly due to crystalline anisotropy becoming more important at this sample thickness than it is in bulk samples. Furthermore, we find that a metastable skyrmion state can be observed at low temperature by field cooling through the equilibrium skyrmion pocket in both samples. In contrast to the behavior in bulk samples, the volume fraction of metastable skyrmions does not significantly depend on cooling rate. We show that a possible explanation for this is the change in the lowest temperature of the skyrmion state in this lamellae compared to bulk, without requiring different energetics of the skyrmion state. arXiv:1909.07855v1 [cond-mat.str-el]

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“…10 Skyrmions can also exist in systems with inversion symmetry, where competing magnetic interactions stabilize the skyrmions. [11][12][13][14][15][16] In thin films, skyrmions appear as disk-like excitations and in bulk materials, skyrmions are line-like excitations. Skyrmions can be manipulated by various external drives, such as electric current, electric field, thermal gradient, etc.…”

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“…33 Note that the asymmetry only appears in k z along the field direction, while the dispersion with respect to k x and k y remain symmetric. Therefore for a thin film with a normal magnetic field, the magnon dispersion is symmetric with respect to the arXiv:1901.03812v2 [cond-mat.mtrl-sci] 16 Apr 2019…”

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Kelvin modes of a skyrmion line in chiral magnets and the associated magnon transport

2019

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Magnetic skyrmions in bulk crystals are line-like topologically protected spin textures. They allow for the propagation of magnons along the skyrmion line but are localized inside the skyrmion line. Analogous to the vortex line, these propagating modes are the Kelvin modes of a skyrmion line. In crystals without an inversion center, it is known that the magnon dispersion in the ferromagnetic state is asymmetric in the wavevector. It is natural to expect that the dispersion of the Kelvin modes is also asymmetric with respect to the wavevector. We study the Kelvin modes of a skyrmion line in the ferromagnetic background. In contrast, we find that the lowest Kelvin mode is symmetric in the wavevector in the low energy region despite the inversion symmetry breaking. Other Kelvin modes below the magnon continuum are asymmetric, and most of them have a positive group velocity. Our results suggest that a skyrmion line can function as a one-way waveguide for magnons.Lord Kelvin calculated stable propagating wave modes along a straight vortex tube of uniform vorticity in a classical fluid about 130 years ago. 1 These modes were later called Kelvin modes. The Kelvin modes in quantized vortex lines were subsequently studied 2,3 and observed experimentally 4 in quantum superfluids. The spectrum of the Kelvin modes in the long wavelength limit is ω = 2 k 2 2m ln(1/kξ), where m is the mass of a particle in the superfluid, k is the momentum, and ξ is the healing length.

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Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet

Cited by 604 publications

References 53 publications

Static and dynamic properties of bimerons in a frustrated ferromagnetic monolayer

Static and dynamic properties of bimerons in a frustrated ferromagnetic monolayer

Stability and metastability of skyrmions in thin lamellae ofCu2OSeO3

Kelvin modes of a skyrmion line in chiral magnets and the associated magnon transport

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