arXiv subjects

Elena Y. Vedmedenko

Publications and source records attributed to Elena Y. Vedmedenko.

At least 19 recordsLinked to original sources

arXiv2026

Creation and motion of antiferromagnetic skyrmions by edge manipulation

Magnetic racetrack architectures that use topological magnetic particles to store information are one of the most promising concepts for future storage applications. Antiferromagnetic racetracks are particularly appealing as they are not susceptible to external magnetic fields. State-of-the-art racetracks use magnetic fields, spin-transfer and spin-orbit torques caused by electric currents to move the bits across the entire circuit. However, the application of currents in many antiferromagnetic racetracks is limited because many of them are insulating. Recently, however, a concept for ferromagnetic racetrack memories that are free of global driving forces has been proposed. It has been demonstrated that various topological entities can be generated and transported over long distances solely through local magnetization rotation at the sample boundaries, independent of global driving forces. Here, we demonstrate that the local rotation of magnetization at the boundary of an antiferromagnetic sample can be exploited in racetracks to efficiently generate and transmit antiferromagnetic skyrmions. Additionally, we demonstrate that local switching of staggered magnetization at the edge of an antiferromagnetic racetrack can be even more successful than the rotational procedure. A comparison of ferromagnetic and antiferromagnetic processing of skyrmionic bits, together with energy considerations, shows that this procedure is fairly efficient in antiferromagnets.

cond-mat.mes-hall↗

arXiv2026

Effects of interlayer Dzyaloshinskii-Moriya interaction on the shape and dynamics of magnetic twin-skyrmions

Magnetic skyrmions have been proposed as promising candidates for storing information due to their high stability and easy manipulation by spin-polarized currents. Here, we study how these properties are influenced by the interlayer Dzyaloshinskii--Moriya interaction (IL-DMI), which stabilizes twin-skyrmions in magnetic bilayers. We find that the spin configuration of the twin-skyrmion adapts to the direction of the IL-DMI by elongating or changing the helicities in the two layers. Driving the skyrmions by spin-polarized currents in the current-perpendicular-to-plane configuration, we observe significant changes either in the skyrmion velocity or in the skyrmion Hall angle depending on the current polarization. These findings unravel further prospects for skyrmion manipulation enabled by the IL-DMI.

cond-mat.mes-hall↗

arXiv2024

Boundary conditions for and ferromagnetic resonance spectra of magnetic bilayers coupled by interlayer Dzyaloshinskii-Moriya interactions

Interfacial Dzyaloshinskii-Moriya interaction (IF-DMI) leads to non-collinear spin configurations within the magnetic layers of multilayer heterostructures, while its interlayer counterpart (IL-DMI) minimizes chiral states between the layers. Here, we demonstrate that the symmetries of these interactions are very different, even though both arise from pairwise exchange interactions between magnetic sites mediated by nonmagnetic atoms. By deriving new boundary conditions for the exchange operator and solving the associated boundary value problem, we show that, unlike IF-DMI, which does not contribute to the FMR frequencies, IL-DMI alters the frequencies of the fundamental FMR modes and can be separated from other contributions in an FMR experiment.

cond-mat.mes-hall↗

arXiv2024

Interlayer and interfacial Dzyaloshinskii-Moriya interaction in magnetic trilayers: first-principles calculations

We determine the Dzyaloshinskii-Moriya interaction within and between two magnetic cobalt layers separated by a non-magnetic spacer through ab initio calculations. We investigate different materials for the non-magnetic layer, focusing on the experimentally realized Co/Ag/Co system. We laterally shift the atoms in the non-magnetic layer to achieve the symmetry breaking required for the interlayer Dzyaloshinskii-Moriya interaction. We compare the resulting interactions with the Lévy-Fert model and observe a good overall agreement between the model and the ab initio calculations for the dependence on the atomic positions. Additionally, we derive a formula for the strength of the interlayer isotropic exchange interaction depending on the position of the atoms in the non-magnetic layer and compare it to the first-principles results. We investigate the limitations of the Lévy-Fert model by turning off the spin-orbit coupling separately on the non-magnetic and magnetic atoms and by studying the effect of band filling. Our work advances the understanding of the microscopic mechanisms of the interlayer Dzyaloshinskii-Moriya interaction and gives insight into possible new material combinations with strong interlayer Dzyaloshinskii-Moriya interaction.

cond-mat.mtrl-sci↗

arXiv2024

Large diversity of magnetic phases in two-dimensional magnets with spin-orbit coupling and superconductivity

We classify the magnetic ground states of a 2D lattice of localized magnetic moments which are coupled to a superconducting substrate with Rashba-spin-orbit coupling. We discover a rich magnetic phase diagram with surprisingly complex structures including 2q-spin-spirals, a 2x2-periodic pattern, and skyrmion lattices, self-consistently, using an effective classical spin Hamiltonian and show that the system hosts non-zero 4-spin interactions. Our in-depth analysis of about ten thousand magnetic configurations becomes feasible using contrastive clustering, a recent advanced unsupervised machine learning technique. This work proposes simple few-band systems for non-collinear magnetic states and stimulates further research on topological effects in their self-consistent electronic structure.

cond-mat.supr-con↗

arXiv2024

Preservation of scalar spin chirality across a metallic spacer in synthetic antiferromagnets with chiral interlayer interactions

Chiral magnetic textures are key for the development of modern spintronic devices. In multilayered thin films, these are typically stabilized via the interfacial intralayer Dzyaloshinskii-Moriya interaction (DMI). Additionally, it has been recently observed that DMI may also promote vector spin chirality along the third dimension, coupling spins in different magnetic layers via non-magnetic spacer layers, an effect referred to as interlayer DMI (IL-DMI). This interaction holds promise for 3D nanomagnetism, from the creation of 3D spin structures such as hopfions to new forms of magnetic functionality in the vertical direction via remote control of chiral spin states. Here, we investigate via magnetic X-ray scattering and imaging techniques the chiral nature of orthogonal magnetic states that form in a synthetic antiferromagnet with IL-DMI. We find that the vector spin chirality of the textures formed in an in-plane layer is determined by the net out-of-plane spin configuration of a neighboring layer, leading as a result to complex spin states across a metallic interface where the overall scalar spin chirality is preserved. This work thus uncovers a new flavor of chiral interlayer interactions, demonstrating new ways to control magnetic chirality in three dimensions.

cond-mat.mes-hall↗

arXiv2023

Observation and formation mechanism of 360° domain wall rings in Synthetic Anti-Ferromagnets with interlayer chiral interactions

The Interlayer Dzyaloshinskii-Moriya interaction (IL-DMI) chirally couples spins in different ferromagnetic layers of multilayer heterostructures. So far, samples with IL-DMI have been investigated utilizing magnetometry and magnetotransport techniques, where the interaction manifests as a tunable chiral exchange bias field. Here, we investigate the nanoscale configuration of the magnetization vector in a synthetic anti-ferromagnet (SAF) with IL-DMI, after applying demagnetizing field sequences. We add different global magnetic field offsets to the demagnetizing sequence in order to investigate the states that form when the IL-DMI exchange bias field is fully or partially compensated. For magnetic imaging and vector reconstruction of the remanent magnetic states we utilize X-ray magnetic circular dichroism photoemission electron microscopy, evidencing the formation of 360$^{\circ}$ domain wall rings of typically 0.5-3.0 $μm$ in diameter. These spin textures are only observed when the exchange bias field due to the IL-DMI is not perfectly compensated by the magnetic field offset. From a combination of micromagnetic simulations, magnetic charge distribution and topology arguments, we conclude that a non-zero remanent effective field with components both parallel and perpendicular to the anisotropy axis of the SAF is necessary to observe the rings. This work shows how the exchange bias field due to IL-DMI can lead to complex metastable spin states during reversal, important for the development of novel spintronic devices.

cond-mat.mes-hall↗

arXiv2022

Creating arbitrary sequences of mobile magnetic skyrmions and antiskyrmions

Magnetic skyrmions and their anti-particles, the antiskyrmions, are stable magnetic solitons existing down to the nanometer scale. Their stability and size as well as the possibility to propel them by, e.g., electric currents make them promising candidates for the use in memory devices, such as racetrack memories. Skyrmions and antiskyrmions share those same advantages individually, but may annihilate each other when they coexist in the same device. Yet, combining them to represent logical bits of 0 (skyrmion) and 1 (antiskyrmion) in one device opens new possibilities to create new types of densely packed racetrack memory devices. For this, a controlled creation and annihilation procedure, i.e., a writing or deletion operation, is necessary. Here, we propose a method to create arbitrary sequences of coexisting skyrmions and antiskyrmions by rotations of the magnetic moments at the edge of a rectangular slab. The skyrmions and antiskyrmions remain stable and do not annihilate each other.

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arXiv2022

Controlled Creation of Quantum Skyrmions

We study the creation of quantum skyrmions in quadratic nanoscopic lattices of quantum spins coupled by Dzyaloshinkii-Moriya and exchange interactions. We numerically show that different kinds of quantum skyrmions, characterized by the magnitude of their spin expectation values and strong differences in their stability, can appear as ground state and as metastable excitations. In dependence on the coupling strengths and the lattice size, an adiabatic rotation scheme of the magnetization at the lattice boundaries allows for a controlled creation of quantum skyrmions.

cond-mat.mes-hall↗

arXiv2022

Topological characterization of dynamic chiral magnetic textures using machine learning

Recently proposed spintronic devices use magnetic skyrmions as bits of information. The reliable detection of those chiral magnetic objects is an indispensable requirement. Yet, the high mobility of magnetic skyrmions leads to their stochastic motion at finite temperatures, which hinders the precise measurement of the topological numbers. Here, we demonstrate the successful training of artificial neural networks to reconstruct the skyrmion number in confined geometries from time-integrated, dimensionally reduced data. Our results prove the possibility to recover the topological charge from a time-averaged measurement and hence smeared dynamic skyrmion ensemble, which is of immediate relevance to the interpretation of experimental results, skyrmion-based computing, and memory concepts

cond-mat.mes-hall↗

arXiv2022

Complex magnetic ground states and topological electronic phases of atomic spin chains on superconductors

Understanding the magnetic properties of atomic chains on superconductors is an essential cornerstone on the road towards controlling and constructing topological electronic matter. Yet, even in simple models, the magnetic ground states remain debated. Ferromagnetic (FM), antiferromagnetic (AFM), and spin spiral configurations have been suggested and experimentally detected, while non-coplanar and complex collinear phases have been additionally conjectured. Here, we resolve parts of the controversy by determining the magnetic ground states of chains of magnetic atoms in proximity to a superconductor with Monte-Carlo methods. We confirm the existence of FM, AFM and spin spiral ground states, exclude non-coplanar phases in the model and clarify the parametric region of a $\uparrow\uparrow\downarrow\downarrow$-phase. We further identify a number of novel complex collinear spin configurations, including the periodic spin configurations $\uparrow\uparrow\uparrow\downarrow$, and $\uparrow \uparrow \uparrow \downarrow \uparrow \downarrow \downarrow \downarrow \uparrow \downarrow$, which are in some cases combined with harmonic and anharmonic spirals to form the ground state. We topologically classify the electronic structures, investigate their stability against increasing the superconducting order parameter, and explain the complex collinear order by an effective Heisenberg model with dominant four-spin interactions.

cond-mat.supr-con↗

arXiv2022

Spin revolution

The classical laws of physics are usually invariant under time reversal. Here, we reveal a novel class of magnetomechanical effects rigorously breaking time-reversal symmetry. The effect is based on the mechanical rotation of a hard magnet around its magnetization axis in the presence of friction and an external magnetic field, which we call spin revolution. The physical reason for time-reversal symmetry breaking is the spin revolution and not the dissipation. The time-reversal symmetry breaking leads to a variety of unexpected effects including upward propulsion on vertical surfaces defying gravity as well as magnetic gyroscopic motion that is perpendicular to the applied force. In contrast to the spin, the angular momentum of spin revolution can be parallel or antiparallel to the equilibrium magnetization. The spin revolution emerges spontaneously, without external rotations, and offers various applications in areas such as magnetism, robotics and energy harvesting.

cond-mat.mes-hall↗

arXiv2022

Nanoscale Skyrmions on a Square Atomic Lattice

Spin-polarized scanning tunneling microscopy has been applied to study non-collinear spin textures of a Mn monolayer on a four-fold symmetric W(001) substrate revealing a zero-field spin spiral ground state and two different types of rotational domain walls. With an applied magnetic field of 9 T, we observe a coexistence of the spin spiral and the skyrmion phase, even though a previous theoretical study reported that the phase transition occurs at 18 T. The skyrmions show a roughly hexagonal arrangement despite the square lattice symmetry of the W(001) substrate. Based on a reduced set of energy parameters, we are able to describe the experimental findings and to analyze the topological properties of the rotational domain walls.

cond-mat.mes-hall↗

arXiv2021

Zero-field skyrmionic states and in-field edge-skyrmions induced by boundary tuning

When magnetic skyrmions are moved via currents, they do not strictly travel along the path of the current, instead their motion also gains a transverse component. This so-called skyrmion Hall effect can be detrimental in potential skyrmion devices because it drives skyrmions towards the edge of their hosting material where they face potential annihilation. Here we experimentally modify a skyrmion model system - an atomic Pd/Fe bilayer on Ir(111) - by decorating the film edge with ferromagnetic Co/Fe patches. Employing spin-polarized scanning tunneling microscopy, we demonstrate that this ferromagnetic rim prevents skyrmion annihilation at the film edge and stabilizes skyrmions and target states in zero field. Furthermore, in an external magnetic field the Co/Fe rim can give rise to skyrmions pinned to the film edge. Spin dynamics simulations reveal how a combination of different attractive and repulsive skyrmion-edge interactions can induce such an edge-pinning effect for skyrmions.

cond-mat.mes-hall↗

arXiv2020

Rotating edge-field driven processing of chiral spin textures in racetrack devices

Topologically distinct magnetic structures like skyrmions, domain walls, and the uniformly magnetized state have multiple applications in logic devices, sensors, and as bits of information. One of the most promising concepts for applying these bits is the racetrack architecture controlled by electric currents or magnetic driving fields. In state-of-the-art racetracks, these fields or currents are applied to the whole circuit. Here, we employ micromagnetic and atomistic simulations to establish a concept for racetrack memories free of global driving forces. Surprisingly, we realize that mixed sequences of topologically distinct objects can be created and propagated over far distances exclusively by local rotation of magnetization at the sample boundaries. We reveal the dependence between the chirality of the rotation and the direction of propagation and define the phase space where the proposed procedure can be realized. The advantages of this approach are the exclusion of high current and field densities as well as its compatibility with an energy-efficient three-dimensional design.

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arXiv2019

Stochastic dynamics and pattern formation of geometrically confined skyrmions

Ensembles of magnetic skyrmions in confined geometries are shown to exhibit thermally driven motion on two different time scales. The intrinsic fluctuating dynamics ($t\sim 1~$ps) is governed by short-range symmetric and antisymmetric exchange interactions, whereas the long-time limit ($t\gtrsim10\,$ns) is determined by the coaction of skyrmion-skyrmion-repulsion and the system's geometry. Micromagnetic simulations for realistic island shapes and sizes are performed and analyzed, indicating the special importance of skyrmion dynamics at finite temperatures. We demonstrate how the competition between skyrmion mobility and observation time directly affects the addressability of skyrmionic bits, which is a key challenge on the path of developing skyrmion-based room-temperature applications. The presented quasiparticle Monte Carlo approach offers a computationally efficient description of the diffusive motion of skyrmion ensembles in confined geometries, like racetrack memory setups.

cond-mat.mes-hall↗

arXiv2018

Effective damping enhancement in noncollinear spin structures

Damping mechanisms in magnetic systems determine the lifetime, diffusion and transport properties of magnons, domain walls, magnetic vortices, and skyrmions. Based on the phenomenological Landau-Lifshitz-Gilbert equation, here the effective damping parameter in noncollinear magnetic systems is determined describing the linewidth in resonance experiments or the decay parameter in time-resolved measurements. It is shown how the effective damping can be calculated from the elliptic polarization of magnons, arising due to the noncollinear spin arrangement. It is concluded that the effective damping is larger than the Gilbert damping, and it may significantly differ between excitation modes. Numerical results for the effective damping are presented for the localized magnons in isolated skyrmions, with parameters based on the Pd/Fe/Ir(111) model-type system.

cond-mat.mtrl-sci↗

arXiv2018

Localized spin waves in isolated $kπ$ skyrmions

The localized magnon modes of isolated $kπ$ skyrmions on a field-polarized background are analyzed based on the Landau-Lifshitz-Gilbert equation within the terms of an atomistic classical spin model, with system parameters based on the Pd/Fe biatomic layer on Ir(111). For increasing skyrmion order $k$ a higher number of excitation modes are found, including modes with nodes in the radial eigenfunctions. It is shown that at low fields $2π$ and $3π$ skyrmions are destroyed via a burst instability connected to a breathing mode, while $1π$ skyrmions undergo an elliptic instability. At high fields all $kπ$ skyrmions collapse due to the instability of a breathing mode. The effective damping parameters of the spin waves are calculated in the low Gilbert damping limit, and they are found to diverge in the case of the lowest-lying modes at the burst and collapse instabilities, but not at the elliptic instability. It is shown that the breathing modes of $kπ$ skyrmions may become overdamped at higher Gilbert damping values.

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