Observation of room-temperature polar skyrmions

Das, Sujit; Tang, Yun; Hong, Zijian; Gonçalves, M. A. P.; McCarter, Margaret R.; Klewe, Christoph; Nguyen, Kayla X.; Gómez‐Ortiz, Fernando; Shafer, Padraic; Arenholz, Elke; Stoica, Vladimir; Hsu, S.-L.; Wang, B.; Ophus, Colin; Liu, Jianfang; Nelson, Christopher T.; Saremi, Sahar; Prasad, Bhagwati; Mei, Antonio B.; Schlom, Darrell G.; Íñiguez, Jorgé; García‐Fernández, Pablo; Muller, David A.; Chen, Lei; Junquera, Javier; Martin, Lane W.; Ramesh, R.

doi:10.1038/s41586-019-1092-8

Cited by 541 publications

(463 citation statements)

References 46 publications

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“…An application of magnetic field in such a system stabilizes [7,10] skyrmions (Sks) having topologically protected quasiparticle-like spin structure [11][12][13][14][15][16] in a ferromagnetic background. Neel and Bloch type Sks are generally realized respectively in C nv and D n symmetric [3,10] bulk and thin-film materials for wide range of magnetic fields and temperatures [11][12][13][14][15][16][17][18][19][20][21].…”

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confidence: 99%

Theory of the skyrmion, meron, antiskyrmion, and antimeron in chiral magnets

Bera

Mandal

2019

Phys. Rev. Research

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We semi-analytically find closed-form solution of Euler equation for a chiral magnet in terms of a skyrmion or a meron depending on the relative strengths of magnetic anisotropy and magnetic field. We show that the relevant length scales for these solutions primarily depend on the strengths of Dzyaloshinskii-Moriya interaction through its ratios, respectively, with magnetic field and magnetic anisotropy. We thus unambiguously determine the parameter dependencies on the radius of the topological structures particularly of the skyrmions, showing an excellent agreement with experiments and first-principle studies. An anisotropic Dzyaloshinskii-Moriya interaction suitable for thin films made with Cnv symmetric materials is found to stabilize anti-skyrmion and anti-meron, which are prototypical for D 2d symmetric systems, depending on the degree of anisotropy. Based on these solutions, we obtain phase diagram by comparing the energies of various collinear and non-collinear competing phases.

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confidence: 99%

Theory of the skyrmion, meron, antiskyrmion, and antimeron in chiral magnets

Bera

Mandal

2019

Phys. Rev. Research

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“…As a result of the strong RFs, neighboring dipoles can extend at a finite angle with respect to each other, providing the polarization directions with the possibility of rotating from one direction to the opposite direction smoothly. 8,20 A large domain wall density can be speculated from these labyrinth-like short-rangecorrelated domains, and the giant poling electro-strain S pol (0.584%, 0.553%, 0.575%, and 0.315% at 25°C, 70°C, 85°C, and 150°C) for BNT-based solid solutions should have a great relevance to the movement of these domain walls, as provided in Figure 4A,D. Note here that the bipolar E-field (−60 kV/cm ≤ E ≤ 60 kV/cm) is applied on the unpoled sample directly without the pre-polarization treatment, and the first cycle S-E curves reflect the transition process from the initial state to the poling state.…”

Section: Resultsmentioning

confidence: 99%

Domain‐scale imaging to dispel the clouds over the thermal depolarization of Bi_0.5Na_0.5TiO₃‐based relaxor ferroelectrics

Yin

Liu

2019

J Am Ceram Soc

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Thermal depolarization temperature, Td, of ferroelectric oxides Bi0.5Na0.5TiO3 (BNT), where dielectric and piezoelectric signals exhibit remarkable changes, is providing rich research contents but is not well understood yet. Herein, on the domain‐scale, we give the direct and clear real‐space images of thermal depolarization process on BNT‐based complex oxides. As disclosed by the piezoresponse force microscopy (PFM), heating above Td breaks the poling‐induced large‐sized‐oriented domains into smaller sized polar clusters with different orientations, leading to the thermal depolarization phenomenon. Although the poling‐induced domain decays above Td, the broken domains exhibit a rather larger coherence length than that of the incipient labyrinth‐like nano‐domains. During the heating process, BNT possesses a structural transition from the long‐range‐correlated R3c (a−a−a− anti‐phase tilting) to the short‐range‐correlated P4bm (a0a0c+ in‐phase tilting) phase, which should be the fundamental driving force for the fluctuations of poling‐induced large‐sized‐oriented domains. We expect these results will further promote the understanding about the origin of Td in BNT‐based relaxor ferroelectrics, and provide an intuitive method for the characterization of the thermodynamic and kinetic process in this kind of materials.

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“…If the Magnus force is absent, the skyrmion dynamics would be con- sistent with what is found in an overdamped system and the edge transport would be absent. There are also other possible systems that could exhibit edge currents, such as the trochoidal motion of skyrmions in certain bilayer systems [60] as well as the dynamics of anti-skyrmion lattices [77], meron lattices [78], or polar skyrmions [79].…”

Section: Discussionmentioning

confidence: 99%

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

Reichhardt

2019

Phys. Rev. B

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We show that ac driven skyrmion lattices in a weak pinning channel confined by regions of strong pinning exhibit edge transport carried by skipping orbits while skyrmions in the bulk of the channel undergo localized orbits with no net transport. The magnitude of the edge currents can be controlled by varying the amplitude and frequency of the ac drive or by changing the ratio of the Magnus force to the damping term. We identify a localized phase in which the orbits are small and edge transport is absent, an edge transport regime, and a fluctuating regime that appears when the ac drive is strong enough to dynamically disorder the skyrmion lattice. We also find that in some cases, multiple rows of skyrmions participate in the transport due to a drag effect from the skyrmionskyrmion interactions. The edge currents are robust for finite disorder and should be a general feature of skyrmions interacting with confined geometries or inhomogeneous disorder under an ac drive. We show that similar effects can occur for skyrmion lattices at interfaces or along domain boundaries for multiple coexisting skyrmion species. The edge current effect provides a new method to control skyrmion motion, and we discuss the connection of these results with recent studies on the emergence of edge currents in chiral active matter systems and gyroscopic metamaterials.

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Observation of room-temperature polar skyrmions

Cited by 541 publications

References 46 publications

Theory of the skyrmion, meron, antiskyrmion, and antimeron in chiral magnets

Theory of the skyrmion, meron, antiskyrmion, and antimeron in chiral magnets

Domain‐scale imaging to dispel the clouds over the thermal depolarization of Bi_0.5Na_0.5TiO₃‐based relaxor ferroelectrics

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

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Observation of room-temperature polar skyrmions

Cited by 541 publications

References 46 publications

Theory of the skyrmion, meron, antiskyrmion, and antimeron in chiral magnets

Theory of the skyrmion, meron, antiskyrmion, and antimeron in chiral magnets

Domain‐scale imaging to dispel the clouds over the thermal depolarization of Bi0.5Na0.5TiO3‐based relaxor ferroelectrics

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

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Domain‐scale imaging to dispel the clouds over the thermal depolarization of Bi_0.5Na_0.5TiO₃‐based relaxor ferroelectrics