arXiv subjects

Vladyslav M. Kuchkin

Publications and source records attributed to Vladyslav M. Kuchkin.

At least 19 recordsLinked to original sources

arXiv2026

Stability and current-driven dynamics of mixed-topology bimeron clusters

In this work, we study bimerons (in-plane skyrmions) and their clusters composed of states with mixed topological indices. These clusters provide flexibility in controlling the skyrmion Hall angle, which depends on the cluster's total topological charge. First, using the simplest such cluster, a bimeron-antibimeron pair, we examine its stability with the geodesic nudged elastic band method and identify three mechanisms -- bimeron separation, interchange, and annihilation -- with comparable energy barriers that determine the pair's overall stability. This provides an upper bound for the stability of more sophisticated clusters of bimerons and antibimerons. Then, we numerically study the clusters' dynamics for currents applied in-plane and perpendicular to the plane, corresponding to the Zhang-Li and Slonczewski mechanisms. Finally, we analyze the dynamics of a wide variety of bimeron clusters within the Thiele approach and show that their velocities always lie on a specific ellipse whose parameters are fully governed by the model Hamiltonian.

cond-mat.mes-hall↗

arXiv2026

Three-Dimensional Shankar Skyrmions in Frustrated Antiferromagnets

We formulate a continuum theory for three-dimensional (3D) Shankar skyrmions in frustrated chiral antiferromagnets (AFs) and derive the conditions for metastable finite-size $π_3(SO(3))$ solitons. A Derrick--Hobart scaling analysis shows that exchange, Dzyaloshinskii--Moriya interaction (DMI), anisotropy, and frustration can balance to set a finite equilibrium size. We identify two microscopic routes to this common topological and stabilization framework: intrinsic rotation-frame order in noncollinear AFs and an $\mathbb{S}^3$ extension of an amplitude-softened Néel field. In the latter, the smooth four-component texture projects onto a Néel field containing a spatially separated pair of oppositely charged Bloch points. Numerical minimization yields metastable monopole textures, while the effective dynamics identifies coherent breathing oscillations as their characteristic finite-frequency collective mode. Our results provide a microscopic framework for the statics and dynamics of Shankar skyrmions and identify frustrated chiral AFs as promising hosts of 3D non-Abelian topological textures.

cond-mat.mes-hall↗

arXiv2026

Quantum Hopfion rings in the cluster mean-field approximation

We study the quantum properties of two- and three-dimensional spin textures -- $kπ$-skyrmions and hopfion rings -- within the cluster mean-field approximation (CMFA). By combining the CMFA with a symmetrization procedure, we achieve two key advances: the accurate computation of quantum fluctuations in large spin textures and reliable access to metastable states. These challenges are generally insurmountable using standard methods, which are severely limited by the curse of dimensionality and typically restricted to ground-state properties. Exploiting the cylindrical symmetry of the studied magnetic configurations, we construct one-dimensional chain-like clusters that can be efficiently simulated using the density matrix renormalization group method, while inter-cluster interactions are treated at the mean-field level. The resulting spatial profiles of quantum features such as the local variation of the magnetization length in hopfion rings reveal limitations of the classical micromagnetic model and indicate the necessity of its extension. We demonstrate that the recently proposed regularized micromagnetic equation provides a suitable framework for this purpose.

cond-mat.mes-hall↗

arXiv2026

Magnetic skyrmion lattice disclinations in pentagon- and heptagon-shaped FeGe crystals

Magnetic skyrmions in chiral magnets typically arrange into hexagonal lattices, with their structural order influenced by factors such as temperature, external magnetic fields and geometric constraints. While translational defects in skyrmion lattices such as dislocations have been extensively studied, individual angular defects, or disclinations, remain largely unexplored. Here, we report on the stabilization of five-fold and seven-fold disclinations in pentagon- and heptagon-shaped FeGe nanocrystals created using focused ion beam milling. The magnetic and elastic structures of the disclinated lattices are investigated using Fresnel imaging and off-axis electron holography in a transmission electron microscope. The results are supported by micromagnetic simulations and analytical models based on linear elasticity theory.

cond-mat.mtrl-sci↗

arXiv2026

Linked skyrmions in shifted magnetic bilayer

Magnetic solitons have recently attracted significant attention due to their intricate physical properties and potential applications in information processing. The majority of the studies in this field, however, are focused on a particular type of solitons known as skyrmions, characterised by a unit topological charge. Here, we present a shifted magnetic bilayer that can demonstrate magnetic solitons with arbitrary large topological charges. These configurations, which we call linked skyrmions, consist of multiple skyrmions linked together with topological point defects. These topological point defects, termed as anti-aligned points, originate from the mutually orthogonal Dzyaloshinskii-Moriya interaction in two different layers. By tuning the interlayer exchange coupling and the external magnetic field, one can also achieve different ground states in this bilayer. Additionally, the system also demonstrates conventional skyrmion-bags and $kπ$-skyrmions. Finally we propose a suitable material candidate where these magnetic configurations can be realised. Our findings, thus, can provide a way to achieve solitons with large topological charge and realise them in realistic systems.

cond-mat.mes-hall↗

arXiv2025

Regularized Micromagnetic Theory for Bloch Points

Magnetic singularities known as Bloch points (BPs) present a fundamental challenge for micromagnetic theory, which is based on the assumption of a fixed magnetization vector length. Due to the divergence of the effective field at a BP, classical micromagnetics fails to adequately describe BP dynamics. To address this issue, we propose a regularized micromagnetic model in which the magnetization vector can vary in length but not exceed a threshold value. More specifically, the magnetization is treated as an order parameter constrained to a S3-sphere. This constraint respects fundamental properties of local spin expectation values in quantum systems. We derive the corresponding regularized Landau-Lifshitz-Gilbert equation and the analogue of the Thiele equation describing the steady motion of spin textures under various external stimuli. We demonstrate the applicability of our theory by modeling the dynamics of several magnetic textures containing BPs, including domain walls in nanowires, chiral bobbers, and magnetic dipolar strings. The presented results extend micromagnetic theory by incorporating a regularized description of BP dynamics.

cond-mat.mes-hall↗

arXiv2025

Skyrmionic Schrödinger cat states in monoaxial chiral magnets

We study the low-energy excitation spectra of a spin-1/2 quantum Heisenberg model with a monoaxial Dzyaloshinskii-Moriya interaction. Using the density matrix renormalization group method, our analysis reveals a degeneracy between skyrmion and antiskyrmion states, enabling the formation of a mesoscopic Schrödinger cat state - a quantum superposition of these topologically distinct textures. To characterize this nontrivial state, we compute two-point spin correlation functions, highlighting signatures accessible via neutron scattering experiments. Furthermore, we demonstrate that applying a magnetic field gradient induces a coherent time evolution of the cat state, offering a controllable mechanism for its manipulation. These findings provide a framework for the detection of skyrmionic Schrödinger cat states in quantum magnets.

cond-mat.mes-hall↗

arXiv2025

Co-existing magnetization reversal mechanisms in shakti spin ice systems

The switching mechanisms in artificial spin ice systems are investigated with focus on shakti and modified shakti lattices. Minimum energy paths are calculated using the geodesic nudged elastic band (GNEB) method implemented with a micromagnetic description of the system, including the internal magnetic structure of the islands and edge modulations. Two switching mechanisms, uniform magnetization rotation and domain wall formation, are found to have comparable activation energy. The preference for one over the other depends strongly on the saturation magnetization and the magnetic ordering of neighboring islands. Surprisingly, these mechanisms can coexist, leading to an enhanced probability of magnetization reversal. These results provide valuable insight that can help control internal magnetization switching processes in spin ice systems and help predict their thermodynamic properties.

cond-mat.mes-hall↗

arXiv2025

Stability and Nucleation of Dipole Strings in Uniaxial Chiral Magnets

We report on the stability of the magnetic dipole string (DS), a three-dimensional magnetic texture formed by two coupled Bloch points with opposite topological charges, separated by an equilibrium distance. Previous studies demonstrated the stability of such configurations through geometric confinement or coupling with local perturbations in the magnetization field, such as skyrmion strings or dislocations in helical modulations. Here, we show that, in uniaxial chiral magnets, an isolated DS remains stable in an unperturbed vacuum, thus representing a true three-dimensional soliton. The phase diagram illustrates the stability of the DS embedded in the conical or helical phases across a broad range of material parameters and external magnetic fields. Using the geodesic nudged elastic band method applied to a regularized micromagnetic model, we demonstrate that isolated DSs are protected from collapse by an energy barrier. Stochastic spin-lattice simulations demonstrate that DSs can spontaneously nucleate during in-field annealing. This work aims to stimulate the experimental observation of DSs and further exploration of uniaxial chiral magnets.

cond-mat.mes-hall↗

arXiv2024

Symmetry-Governed Dynamics of Magnetic Skyrmions Under Field Pulses

Topological magnetic solitons, such as skyrmions, exhibit intriguing particle-like properties that make them attractive for fundamental research and practical applications. While many magnetic systems can host skyrmions as statically stable configurations, chiral magnets stand out for their ability to accommodate a wide diversity of skyrmions with arbitrary topological charges and varied morphologies. Despite extensive investigation, a complete understanding of chiral magnetic skyrmions has remained elusive. We present a classification of all chiral skyrmions, demonstrating three classes based on their response to external magnetic field pulses: stationary, translating, and rotating. We highlight the role of magnetic texture symmetry in this classification. Skyrmions with varied dynamics offer avenues for exploring phenomena like skyrmion-skyrmion scattering that might be crucial for future applications.

cond-mat.str-el↗

arXiv2024

Quantum and classical magnetic Bloch points

A Bloch point represents a three-dimensional hedgehog singularity of a magnetic vector field in which the magnetization vanishes. However, standard micromagnetic theory, developed for magnetic moments of fixed lengths, lacks full applicability in studying such singularities. To address this gap, we study a Bloch point in a quantum Heisenberg model for the case of spin-1/2 particles. Performing an exact diagonalization of the Hamiltonian as well as using density matrix renormalization group techniques, we obtain the ground state, which can be used to recover the corresponding magnetization profile. Our findings demonstrate a variation of the spin length in the quantum model, leading smoothly to zero magnetization at the Bloch point. Our results indicate the necessity of generalizing the classical micromagnetic model by adding the third degree of freedom of the spins: the ability to change its length. To this end, we introduce the micromagnetic $\mathbb{S}_{3}$-model, which enables the description of magnets with and without Bloch point singularities.

cond-mat.str-el↗

arXiv2023

Skyrmions and antiskyrmions in monoaxial chiral magnets

We show that competition between local interactions in monoaxial chiral magnets provides the stability of two-dimensional (2D) solitons with identical energies but opposite topological charges. These skyrmions and antiskyrmions represent metastable states in a wide range of parameters above the transition into the saturated ferromagnetic phase. The symmetry of the underlying micromagnetic functional gives rise to soliton zero modes allowing efficient control of their translational movement by the frequency of the circulating external magnetic field. We also discuss the role of demagnetizing fields in the energy balance between skyrmion and antiskyrmion and in their stability.

cond-mat.mes-hall↗

arXiv2023

Heliknoton in a film of cubic chiral magnet

Cubic chiral magnets exhibit a remarkable diversity of two-dimensional topological magnetic textures, including skyrmions. However, the experimental confirmation of topological states localized in all three spatial dimensions remains challenging. In this paper, we investigate a three-dimensional topological state called a heliknoton, which is a hopfion embedded into a helix or conic background. We explore the range of parameters at which the heliknoton can be stabilized under realistic conditions using micromagnetic modeling, harmonic transition state theory, and stochastic spin dynamics simulations. We present theoretical Lorentz TEM images of the heliknoton, which can be used for experimental comparison. Additionally, we discuss the stability of the heliknoton at finite temperatures and the mechanism of its collapse. Our study offers a pathway for future experimental investigations of three-dimensional topological solitons in magnetic crystals.

cond-mat.mes-hall↗

arXiv2023

Tailed skyrmions -- an obscure branch of magnetic solitons

We report tailed skyrmions -- a new class of stable soliton solutions of the 2D chiral magnet model. Tailed skyrmions have elongated shapes and emerge in a narrow range of fields near the transition between the spin spirals and the saturated state. We analyze the stability range of these solutions in terms of external magnetic field and magnetocrystalline anisotropy. Minimum energy paths and the homotopies (continuous transitions) between tailed skyrmions of the same topological charge have been calculated using the geodesic nudged elastic bands method. The discovery of tailed skyrmions extends the diversity of already-known solutions illustrated by complex morphology solitons, such as tailed skyrmion bags with and without chiral kinks.

cond-mat.mes-hall↗

arXiv2022

Homotopy transitions and 3D magnetic solitons

This work provides a concept for three-dimensional magnetic solitons based on mapping the homotopy path between various two-dimensional solutions onto the third spatial axis. The representative examples of statically stable configurations of that type in the model of an isotropic chiral magnet are provided. Various static and dynamic properties of such three-dimensional magnetic solitons are discussed in detail.

cond-mat.mes-hall↗

arXiv2022

Chiral standing spin waves in skyrmion lattice

This work studies the resonance excitations of the three-dimensional skyrmions lattice in the finite thickness plate of an isotropic chiral magnet using spin dynamics simulations. We found that the absorption spectra and resonance modes differ from those predicted by the two-dimensional model and the model of the unconfined bulk crystal. The features observed on the spectra can be explained by the formation of chiral standing spin waves, which, contrary to conventional standing spin waves, are characterized by the helical profile of dynamic magnetization of fixed chirality defined by the Dzyaloshinskii-Moriya interaction. In this case, the dynamic susceptibility becomes a function of the plate thickness, which gives rise to an interesting effect that manifests itself in periodical fading of the intensity of corresponding modes and makes excitation of these modes impossible at specific thicknesses.

cond-mat.mes-hall↗

arXiv2021

Magnetic particle-antiparticle creation and annihilation

A fundamental property of particles and antiparticles, such as electrons and positrons, is their ability to annihilate one another. Similar behavior is predicted for magnetic solitons -- localized spin textures that can be distinguished by their topological index $Q$. Theoretically, magnetic topological solitons with opposite values of $Q$, such as skyrmions and their antiparticles -- antiskyrmions -- are expected to be able to merge continuously and to annihilate. However, experimental verification of such particle-antiparticle pair production and annihilation processes has been lacking. Here, we report the creation and annihilation of skyrmion-antiskyrmion pairs in an exceptionally thin film of the cubic chiral magnet B20-type FeGe observed using transmission electron microscopy. Our observations are highly reproducible and are fully consistent with micromagnetic simulations. Our findings provide a new platform for fundamental studies of particles and antiparticles based on magnetic solids and open new perspectives for practical applications of thin films of isotropic chiral magnets.

cond-mat.str-el↗

arXiv2021

Thermal generation of droplet soliton in chiral magnet

Controlled creation of localized magnetic textures beyond conventional $π$-skyrmions is an important problem in the field of magnetism. Here by means of spin dynamics simulations, Monte Carlo simulations and harmonic transition state theory we demonstrate that an elementary chiral magnetic soliton with zero topological charge -- the chiral droplet -- can be reliably created by thermal fluctuations in the presence of the tilted magnetic field. The proposed protocol relies on an unusual kinetics combining the effects of the entropic stabilization and low energy barrier for the nucleation of a topologically-trivial state. Following this protocol by varying temperature and the tilt of the external magnetic field one can selectively generate chiral droplets or $π$-skyrmions in a single system. The coexistence of two distinct magnetic solitons establishes a basis for a rich magnetization dynamics and opens up the possibility for the construction of more complex magnetic textures such as skyrmion bags and skyrmions with chiral kinks.

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