Beyond skyrmions: Review and perspectives of alternative magnetic quasiparticles

Göbel, Börge; Mertig, Ingrid; Tretiakov, Oleg A.

doi:10.1016/j.physrep.2020.10.001

Cited by 440 publications

(322 citation statements)

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“…An enormous effort has been undertaken to find solutions for suppressing this so called skyrmion Hall effect, for example modifying the spin torque 27,28 or using alternative magnetic quasiparticles 29 with a vanishing topological charge (like antiferromagnetic skyrmions [30][31][32][33][34][35] or skyrmioniums [36][37][38] or nano-objects with a broken rotational symmetry (like antiskyrmions 39,40 or bimerons 28,41,42 ). However, as we show in the present paper, the skyrmion Hall effect may even be a favorable feature that can be utilized instead of trying to suppress it.…”

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confidence: 99%

Skyrmion ratchet propagation: utilizing the skyrmion Hall effect in AC racetrack storage devices

Göbel

Mertig

2021

Sci Rep

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Magnetic skyrmions are whirl-like nano-objects with topological protection. When driven by direct currents, skyrmions move but experience a transverse deflection. This so-called skyrmion Hall effect is often regarded a drawback for memory applications. Herein, we show that this unique effect can also be favorable for spintronic applications: We show that in a racetrack with a broken inversion symmetry, the skyrmion Hall effect allows to translate an alternating current into a directed motion along the track, like in a ratchet. We analyze several modes of the ratchet mechanism and show that it is unique for topological magnetic whirls. We elaborate on the fundamental differences compared to the motion of topologically trivial magnetic objects, as well as classical particles driven by periodic forces. Depending on the exact racetrack geometry, the ratchet mechanism can be soft or strict. In the latter case, the skyrmion propagates close to the efficiency maximum.

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confidence: 99%

Skyrmion ratchet propagation: utilizing the skyrmion Hall effect in AC racetrack storage devices

Göbel

Mertig

2021

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“…We begin by recalling that in non relativistic 3D quantum mechanics, the spin states S z , S ji of spinfull particles are characterised by two half integers S z , S ðÞ ,a positive S ≥ 0 and an S z taking 2S þ 1 values bounded as ÀS ≤ S z ≤ S with integral hoppings. For particles with spin 1/2 like electrons, one distinguishes two basis vector states AE 1 2 , 1 2 that are eigenvalues of the scaled Pauli matrix ℏ 2 σ z and the quadratic (Casimir) operator . From these ingredients, we learn that the average…”

Section: Quantum Spin 1/2 Operator and Beyondmentioning

confidence: 99%

“…For generic values of the SU 2 ðÞspin S, the spin operator reads as ℏJ a where the three J a 's are 2S þ 1 ðÞ Â 2S þ 1 ðÞ generators of the SU 2 ðÞgroup satisfying the usual commutation relations J a , J b ½ ¼ iε abc J c with ε abc standing for the completely antisymmetric Levi-Civita tensor with non zero value ε 123 ¼ 1; its inverse is ε cba with ε 123 ¼À1. The time evolution of the spin 1 2 operator ℏ σ a 2 with dynamics governed by a stationary Hamiltonian operator (dH=dt ¼ 0) is given by the Heisenberg representation of quantum mechanics. In this non dissipative description, the time dependence of the spin 1 2 operatorŜ a t ðÞ (the hat is to distinguish the operatorŜ a from classical S a ) is given bŷ…”

Section: Quantum Spin 1/2 Operator and Beyondmentioning

confidence: 99%

“…During the last two decades, the magnetic skyrmions and antiskyrmions have been subject to an increasing interest in connection with the topological phase of matter [1][2][3][4], the spin-tronics [5,6] and quantum computing [7,8]; as well as in the search for advanced applications such as racetrack memory, microwave oscillators and logic nanodevices making skyrmionic states very promising candidates for future low power information technology devices [9][10][11][12]. Initially proposed by T. Skyrme to describe hadrons in the theory of quantum chromodynamics [13], skyrmions have however been observed in other fields of physics, including quantum Hall systems [14,15], Bose-Einstein condensates [16] and liquid crystals [17].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Magnetic Skyrmions: Theory and Applications

Drissi¹,

Saidi²,

Bousmina³

et al. 2021

Magnetic Skyrmions

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Magnetic skyrmions have been subject of growing interest in recent years for their very promising applications in spintronics, quantum computation and future low power information technology devices. In this book chapter, we use the field theory method and coherent spin state ideas to investigate the properties of magnetic solitons in spacetime while focussing on 2D and 3D skyrmions. We also study the case of a rigid skyrmion dissolved in a magnetic background induced by the spin-tronics; and derive the effective rigid skyrmion equation of motion. We examine as well the interaction between electrons and skyrmions; and comment on the modified Landau-Lifshitz-Gilbert equation. Other issues, including emergent electrodynamics and hot applications for next-generation high-density efficient information encoding, are also discussed.

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“…In magnetism, non-collinear spin textures can also be characterized by a topological invariant, albeit defined in real space. This 'topological charge' or 'skyrmion number' Nsk is ±1 for most of the recently observed objects 11,12 , including skyrmions and antiskyrmions, which are mesoscopic magnetic whirls that have been observed in chiral systems [13][14][15] . An integer value of Nsk is guaranteed under the assumption of a continuous spin texture and that the surface on which it resides (the magnetic unit cell or the whole sample depending on the periodicity of the texture) can be mapped to a sphere.…”

Section: Introductionmentioning

confidence: 99%

Observation of fractional spin textures and bulk-boundary correspondence

Parkin

Jena

Göbel

et al. 2021

Preprint

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Recently a zoology of non-collinear chiral spin textures has been discovered, most of which, such as skyrmions and antiskyrmions, have integer topological charges that provides them with enhanced stability. Here we report the experimental real-space observation of the formation and stability of fractional antiskyrmions and fractional elliptical skyrmions in a Heusler material. These fractional objects appear, over a wide range of temperature and magnetic field, at the edges of a sample, whose interior is occupied by an array of nano-objects with integer topological charges, in agreement with our simulations. We explore the evolution of these objects in the presence of magnetic fields and show their interconversion to objects with integer topological charges. This means the topological charge can be varied continuously. These fractional spin textures are not just another type of skyrmion, but are essentially a new state of matter that emerges and lives only at the boundary of a magnetic system. Moreover, they form the basis for topological quantum effects arising from the magnonic excitations around a skyrmion lattice. The coexistence of both integer and fractionally charged spin textures in the same material makes the Heusler family of compounds unique for the manipulation of the real-space topology of spin textures and thus an exciting platform especially for the future exploration of the magnonic bulk-boundary correspondence.

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Beyond skyrmions: Review and perspectives of alternative magnetic quasiparticles

Cited by 440 publications

References 210 publications

Skyrmion ratchet propagation: utilizing the skyrmion Hall effect in AC racetrack storage devices

Skyrmion ratchet propagation: utilizing the skyrmion Hall effect in AC racetrack storage devices

Magnetic Skyrmions: Theory and Applications

Observation of fractional spin textures and bulk-boundary correspondence

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