Biskyrmion lattices in centrosymmetric magnetic films

We discuss a geometric perspective on chiral ferromagnetism. Much like gravity becomes the effect of spacetime curvature in theory of relativity, the Dzyaloshinski-Moriya interaction arises in a Heisenberg model with nontrivial spin parallel transport. The Dzyaloshinskii-Moriya vectors serve as a background SO(3) gauge field. In 2 spatial dimensions, the model is partly solvable when an applied magnetic field matches the gauge curvature. At this special point, solutions to the Bogomolny equation are exact excited states of the model. We construct a variational ground state in the form of a skyrmion crystal and confirm its viability by Monte Carlo simulations. The geometric perspective offers insights into important problems in magnetism, e.g., conservation of spin current in the presence of chiral interactions.

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“…Earlier uses of the Weierstrass elliptic functions to describe soliton lattices can be found in Refs. [34,35].…”

Section: High-energy Skyrmion Crystalmentioning

confidence: 99%

Chiral magnetism: a geometric perspective

2021

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“…They are analogous to bi-skyrmions and bi-antiskyrmions observed in nonchiral frustrated magnetic films [30][31][32][33] , but with zero separation between the antiskyrmions 33 .…”

Section: Cooling With An Applied Magnetic Fieldmentioning

confidence: 57%

“…The most prominent example of chiral interactions is the NN DMI, arising in noncentrosymmetric lattices lacking space-inversion symmetry. Moreover, TSTs can form in centrosymmetric materials due to nonchiral interactions [24][25][26][27][28][29][30][31][32][33][34][35] , such as dipolar interactions 24,26,30 , magnetic anisotropy 29,34 , quantum fluctuations 36 , and static random fields 34,35 . In the nonchiral magnetic films, the vorticity and helicity act as additional degrees of freedom, relevant for spintronic and topological applications [30][31][32][33] .…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, TSTs can form in centrosymmetric materials due to nonchiral interactions [24][25][26][27][28][29][30][31][32][33][34][35] , such as dipolar interactions 24,26,30 , magnetic anisotropy 29,34 , quantum fluctuations 36 , and static random fields 34,35 . In the nonchiral magnetic films, the vorticity and helicity act as additional degrees of freedom, relevant for spintronic and topological applications [30][31][32][33] . An external magnetic field usually assists the formation of TSTs in chiral and nonchiral magnetic films.…”

Section: Introductionmentioning

confidence: 99%

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Whirling interlayer fields as a new source of stable topological order in moiré CrI3

Ghader¹,

Jabakhanji²,

Stroppa³

2021

Preprint

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The moiré engineering of two-dimensional magnets opens unprecedented opportunities to design novel magnetic states via the stacking-dependent magnetism. Here, we explore the formation and control of ground state topological spin structures (TSTs) in moiré CrI3 without including the nearest-neighbor (NN) Dzyaloshinskii-Moriya interactions (DMI) and dipolar interactions in the theoretical approach. Using stochastic Landau-Lifshitz-Gilbert simulations, we unveil the emergence of vortex and antivortex interlayer exchange fields at large moiré periodicity. The whirling fields stabilize spontaneous and field-assisted ground state TSTs with various topologies, including skyrmionic clusters with high topological charges. Furthermore, by examining the effect of the Kitaev interaction and the next NN DMI, we propose the latter as the unique spin-orbit coupling mechanism compatible with the experimental results on monolayer and twisted CrI3. Therefore, our study goes beyond the current knowledge about TSTs in moiré magnets, opens exciting opportunities for moiré skyrmionics, and uncovers the spin-orbit coupling in CrI3.

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“…Indirect evidence for the presence of a topologically nontrivial state has been reported for these materials, and other Heusler materials related to the antiskyrmion hosts [9][10][11][12], however direct evidence for both the biskyrmion and antiskyrmion states has thus far relied on Lorentz Transmission Electron Microscopy (LTEM). However, this identification is controversial, as further LTEM and X-ray holography measurements of MnNiGa suggest that the LTEM images can be explained as reflecting a more conventional type-II magnetic bubble state [13], while theoretical studies continued to support the existence of biskyrmions in centrosymmetric magnetic films [14]. Nevertheless, these materials remain of interest as a result of their complex magnetic behavior.…”

Section: Introductionmentioning

confidence: 99%

Spin dynamics in bulk MnNiGa and Mn1.4Pt0.9Pd0.1Sn investigated by muon spin relaxation

et al. 2021

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We report the results of muon-spin relaxation and magnetometry investigations of bulk Mn1.4Pt0.9Pd0.1Sn and MnNiGa, two materials that have been proposed to host topological magnetic states in thin lamellae (antiskyrmions for Mn1.4Pt0.9Pd0.1Sn and biskyrmions for MnNiGa), and show spin reorientation transitions in the bulk. Our measurements reveal dynamic fluctuations surrounding the magnetic phase transitions in each material. In particular, we demonstrate that the behavior approaching the higher-temperature transitions reflects a decrease in the frequency of dynamics with temperature. At low temperatures the two systems both show spin dynamics over a broad range of frequencies that persist below the respective spin reorientation transitions.

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Biskyrmion lattices in centrosymmetric magnetic films

Cited by 24 publications

References 31 publications

Chiral magnetism: a geometric perspective

Chiral magnetism: a geometric perspective

Whirling interlayer fields as a new source of stable topological order in moiré CrI3

Spin dynamics in bulk MnNiGa and Mn1.4Pt0.9Pd0.1Sn investigated by muon spin relaxation

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