Formation of a topological monopole lattice and its dynamics in three-dimensional chiral magnets

Yang, Seong-Gyu; Liu, Ye-Hua; Han, Jung Hoon

doi:10.1103/physrevb.94.054420

Cited by 27 publications

(15 citation statements)

References 36 publications

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“…For more comparison, we simulated the current-driven dynamics of a ferrimagnetic skyrmion (see Methods for more modeling details) in a checkerboard-like two-sublayer spin system based on the G-type antiferromagnetic structure with simple square lattices 20 , 30 , 31 , where the two sublayers, corresponding to Gd and FeCo, are coupled in a ferrimagnetic manner with a net saturation magnetization, while each sublayer is ferromagnetically ordered. We have also examined simulations using the two-sublattice model with classic J 1 - J 2 - J 2 ′ Heisenberg exchange interactions as shown in Supplementary Figs.…”

Section: Resultsmentioning

confidence: 99%

Current-driven dynamics and inhibition of the skyrmion Hall effect of ferrimagnetic skyrmions in GdFeCo films

et al. 2018

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Magnetic skyrmions are swirling magnetic textures with novel characteristics suitable for future spintronic and topological applications. Recent studies confirmed the room-temperature stabilization of skyrmions in ultrathin ferromagnets. However, such ferromagnetic skyrmions show an undesirable topological effect, the skyrmion Hall effect, which leads to their current-driven motion towards device edges, where skyrmions could easily be annihilated by topographic defects. Recent theoretical studies have predicted enhanced current-driven behavior for antiferromagnetically exchange-coupled skyrmions. Here we present the stabilization of these skyrmions and their current-driven dynamics in ferrimagnetic GdFeCo films. By utilizing element-specific X-ray imaging, we find that the skyrmions in the Gd and FeCo sublayers are antiferromagnetically exchange-coupled. We further confirm that ferrimagnetic skyrmions can move at a velocity of ~50 m s−1 with reduced skyrmion Hall angle, |θSkHE| ~ 20°. Our findings open the door to ferrimagnetic and antiferromagnetic skyrmionics while providing key experimental evidences of recent theoretical studies.

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Section: Resultsmentioning

confidence: 99%

Current-driven dynamics and inhibition of the skyrmion Hall effect of ferrimagnetic skyrmions in GdFeCo films

et al. 2018

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“…In the three dimensional magnets, the skyrmion usually forms rod-like object along the external magnetic field [14][15][16][17][18][19][20][21][22][23][24][25] . When the meandering degree of freedom is introduced, it is better to consider it as skyrmion string.…”

Section: Bulk and Surface Topological Indices For A Skyrmion String: mentioning

confidence: 99%

“…2 Department of Applied Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. * email: wataru@riken.jp sometimes called (anti)hedgehog or (anti)monopole 14,16,[20][21][22]30 . In the present paper, we use the word, (anti) monopole, to express the topological defect on the skyrmion string.…”

Section: Openmentioning

confidence: 99%

Bulk and surface topological indices for a skyrmion string: current-driven dynamics of skyrmion string in stepped samples

Koshibae

Nagaosa

2020

Sci Rep

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The magnetic skyrmion is a topological magnetic vortex, and its topological nature is characterized by an index called skyrmion number which is a mapping of the magnetic moments defined on a two-dimensional space to a unit sphere. In three-dimensions, a skyrmion, i.e., a vortex penetrating though the magnet naturally forms a string, which terminates at the surfaces of the magnet or in the bulk. For such a string, the topological indices, which control its topological stability are less trivial. Here, we study theoretically, in terms of numerical simulation, the dynamics of current-driven motion of a skyrmion string in a film sample with the step edges on the surface. In particular, skyrmion–antiskyrmion pair is generated by driving a skyrmion string through the side step with an enough height. We find that the topological indices relevant to the stability are the followings; (1) skyrmion number along the developed surface, and (2) the monopole charge in the bulk defined as the integral over the surface enclosing a singular magnetic configuration. As long as the magnetic configuration is slowly varying, the former is conserved while its changes is associated with nonzero monopole charge. The skyrmion number and the monoplole charge offer a coherent understanding of the stability of the topological magnetic texture and the nontrivial dynamics of skyrmion strings.

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“…1(b)] [14,15]. Remarkably, the magnetic periods of these 3Q-and 4Q-HLs are very short ∼ 2-3 nm, in contrast to most of the skyrmion lattices.Such magnetic HLs have been theoretically studied prior to the experimental discovery, e.g., by the Ginzburg-Landau theory [16], variational calculations [17], and Monte Carlo (MC) simulations [18]. The variational study for a classical spin model showed that the 3Q-HL is not stabilized, whereas the 4Q-HL is obtained in an applied magnetic field [17].…”

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confidence: 99%

Magnetic hedgehog lattices in noncentrosymmetric metals

et al. 2020

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Magnets with noncentrosymmetric lattice structures can host a three-dimensional noncoplanar spin texture called the magnetic hedgehog lattice (HL) with a periodic array of magnetic monopoles and anti-monopoles. Despite recent discovery of two types of short-period HLs in MnSi1−xGex, their microscopic origin remains elusive. Here, we study the stability of such magnetic HLs for an effective spin model with long-range interactions arising from the itinerant nature of electrons. By variational calculations and simulated annealing, we find that the HLs are stabilized in the ground state at zero magnetic field by the synergetic effect of the antisymmetric exchange interactions generated by the spin-orbit coupling and the multiple-spin interactions generated by the spin-charge coupling. We also clarify the full phase diagram in the magnetic field, which includes multiple phase transitions with changes in the number of monopoles and anti-monopoles.Chirality, often termed as handedness, is a key concept in a broad field of science, ranging from particle physics to biology. In condensed matter physics, chiral magnetic textures, which break both inversion and mirror symmetries in additon to time-reversal symmetry, have recently attracted considerable attention for potential applications to next-generation electronic devices. There are a variety of the chiral magnetic textures, such as skyrmion lattices [1] and chiral soliton lattices [2]. Noncollinear and noncoplanar spin arrangements in these textures generate emergent electromagnetic fields through the Berry phase mechanism, which induce unconventional transport, optical, and magnetoelectric properties [3][4][5].Recently, a three-dimensional chiral magnetic texture, which is called the hedgehog lattice (HL), was discovered in the B20-type compound MnGe [6,7]. The magnetic structure is characterized by cubic three wave vectors, and hence, it is referred as the triple-Q hedgehog lattice (3Q-HL) [ Fig. 1(a)]. The 3Q-HL has a periodic array of hyperbolic hedgehog and anti-hedgehog spin textures, which generates an emergent magnetic field with a periodic array of radial hedgehogs and anti-hedgehogs regarded as magnetic monopoles and anti-monopoles, as shown in Fig. 1(c) [8][9][10]. The peculiar magnetic field was discussed as a source of the enormous topological Hall effect [11] and thermoelectoric effect [12,13]. In addition, in MnSi 1−x Ge x , the 3Q-HL changes into a different HL characterized by tetrahedral four wave vectors, dubbed the quadruple-Q hedgehog lattice (4Q-HL) [ Fig. 1(b)] [14,15]. Remarkably, the magnetic periods of these 3Q-and 4Q-HLs are very short ∼ 2-3 nm, in contrast to most of the skyrmion lattices.Such magnetic HLs have been theoretically studied prior to the experimental discovery, e.g., by the Ginzburg-Landau theory [16], variational calculations [17], and Monte Carlo (MC) simulations [18]. The variational study for a classical spin model showed that the 3Q-HL is not stabilized, whereas the 4Q-HL is obtained in an applied magnetic field [17]. The 4Q...

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Formation of a topological monopole lattice and its dynamics in three-dimensional chiral magnets

Cited by 27 publications

References 36 publications

Current-driven dynamics and inhibition of the skyrmion Hall effect of ferrimagnetic skyrmions in GdFeCo films

Current-driven dynamics and inhibition of the skyrmion Hall effect of ferrimagnetic skyrmions in GdFeCo films

Bulk and surface topological indices for a skyrmion string: current-driven dynamics of skyrmion string in stepped samples

Magnetic hedgehog lattices in noncentrosymmetric metals

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