Multiple low-temperature skyrmionic states in a bulk chiral magnet

Bannenberg, Lars J.; Wilhelm, H.; Cubitt, R.; Labh, A.; Schmidt, Marcus; Lelièvre-Berna, E.; Pappas, C.; Mostovoy, Maxim; Leonov, A. O.

doi:10.1038/s41535-019-0150-7

Cited by 59 publications

(74 citation statements)

References 52 publications

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“…As a result, large cooling rates are required to stabilize a significant population of metastable skyrmions in bulk samples (> 40 K/min for 50% skyrmion population in bulk Cu 2 OSeO 3 ) [26]. This presents a limitation to the study and use of metastable skyrmions, which has been previously alleviated using rapid heat pulses from lasers [27] or electrical heaters [28] to form the metastable state, both of which are very energy intensive methods.…”

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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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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“…Insulating Cu 2 OSeO 3 (CSO) has gained notable interest due to its magnetoelectric coupling and is considered as an ideal platform to achieve electric field control of SkLs. Recently, an intriguing discovery of a new skyrmion phase (35) and of low-temperature skyrmions (36,37) has been made in CSO crystals, implying richer phase diagrams. The existence of two distinct skyrmion phases in a multiferroic material could be a generic character of underlying physics and may assist in skyrmion manipulation (36).…”

Section: Introductionmentioning

confidence: 99%

Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu ₂ OSeO ₃

et al. 2020

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Topologically nontrivial spin textures such as vortices, skyrmions, and monopoles are promising candidates as information carriers for future quantum information science. Their controlled manipulation including creation and annihilation remains an important challenge toward practical applications and further exploration of their emergent phenomena. Here, we report controlled evolution of the helical and skyrmion phases in thin films of multiferroic Te-doped Cu 2 OSeO 3 as a function of material thickness, dopant, temperature, and magnetic field using in situ Lorentz phase microscopy. We report two previously unknown phenomena in chiral spin textures in multiferroic Cu 2 OSeO 3 : anisotropic scaling and channeling with a fixed-Q state. The skyrmion channeling effectively suppresses the recently reported second skyrmion phase formation at low temperature. Our study provides a viable way toward controlled manipulation of skyrmion lattices, envisaging chirality-controlled skyrmion flow circuits and enabling precise measurement of emergent electromagnetic induction and topological Hall effects in skyrmion lattices.

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“…The experimental findings hint that cubic anisotropy in Cu 2 OSeO 3 also influences the skyrmion nucleation via two different mechanisms [24]: (i) thermodynamically stable skyrmions may appear via rupture formation of metastable spiral states with wave vectors perpendicular to the field (in the case of Cu 2 OSeO 3 along [100] and [010]); (ii) skyrmions may appear in the form of torons [26] (a localized particle consisting of two Bloch points at finite distance and a convex-shaped skyrmion stretching between them) generated by the inhomogeneous magnetic environment provided by the smooth transition from one tilted spiral domain to another [22].…”

Section: Introductionmentioning

confidence: 90%

“…Recently, a new impetus to those theoretical considerations was provided by the reported LT-SkL in the bulk-insulating cubic helimagnet Cu 2 OSeO 3 [22,23]. A LT-SkL was shown to be stabilized by cubic anisotropy for a magnetic field applied along [001] [23,24], the easy direction of the cubic anisotropy [8,21]. Additionally, it was shown that the role of cubic anisotropy is not limited to the SkL stability but also leads to many other remarkable phenomena.…”

Section: Introductionmentioning

confidence: 99%

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Skyrmion clusters and conical droplets in bulk helimagnets with cubic anisotropy

Leonov

Pappas

2019

Phys. Rev. B

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Recent experimental findings in the bulk cubic helimagnet and Mott insulator Cu 2 OSeO 3 highlight the paramount role of cubic anisotropy in stabilizing novel chiral and skyrmion phases. It was indeed found that if a magnetic field is applied along the easy 001 crystallographic direction, competing cubic and exchange anisotropies tilt the wave vector of the conical spiral away from the magnetic field [Qian et al., Sci. Adv. 4, eaat7323 (2018)]. Furthermore, in this configuration skyrmions have been observed in a broad range of temperatures and magnetic fields [Chacon et al., Nat. Phys. 14, 936 (2018)]. Starting from these experimental observations and on the basis of a phenomenological Dzyaloshinskii theory, we investigate additional implications of the cubic anisotropy for this specified field direction. By including cubic anisotropy we show that the phase transition between the conical and field-polarized or homogeneous states becomes first order. Furthermore, we show that this transition is accompanied by the formation of conical droplets-domains of the conical phase in the homogeneous state. We investigate the internal structure of these droplets, which at their boundaries encompass alternating regions of positive and negative energy densities with respect to the homogeneous state. We thus deduce that these droplets may be zipped and unzipped in phase during the first-order phase transition that occurs by either increasing or decreasing the magnetic field. On the other hand, we show that in the conical phase skyrmions may form clusters due to their attractive mutual interaction. However, in the homogeneous state, the skyrmion-skyrmion interaction becomes repulsive, and the skyrmion clusters expand and disperse isolated skyrmions. This mutual skyrmion repulsion prevents the stabilization of skyrmion clusters even if the energy of isolated skyrmions is lower than that of the homogeneous state. Yet this skyrmion dispersal may be prevented if skyrmions are surrounded by the circular spiral state and form skyrmion bags. Such a scenario could explain the existence of skyrmions in the field-polarized state reported experimentally.

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Multiple low-temperature skyrmionic states in a bulk chiral magnet

Cited by 59 publications

References 52 publications

Stability and metastability of skyrmions in thin lamellae ofCu2OSeO3

Stability and metastability of skyrmions in thin lamellae ofCu2OSeO3

Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu ₂ OSeO ₃

Skyrmion clusters and conical droplets in bulk helimagnets with cubic anisotropy

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Multiple low-temperature skyrmionic states in a bulk chiral magnet

Cited by 59 publications

References 52 publications

Stability and metastability of skyrmions in thin lamellae ofCu2OSeO3

Stability and metastability of skyrmions in thin lamellae ofCu2OSeO3

Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu 2 OSeO 3

Skyrmion clusters and conical droplets in bulk helimagnets with cubic anisotropy

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Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu ₂ OSeO ₃