Skyrmion Motion Research Articles

Guided motion of a magnetic skyrmion by a voltage-controlled strained channel, and logic applications

Guided motion of a magnetic skyrmion by a voltage-controlled strained channel, and logic applications

Skyrmion motion monitoring based on a ferromagnetic nanodot chain

As one of the most promising information carriers, the generation, manipulation, and detection of magnetic skyrmions have emerged as a hot topic in the field of spintronics. However, a major bottleneck to their practical application lies in the existing limitations of detection technology, which fails to accurately locate skyrmions or monitor their real-time motion behavior. In this work, we propose a patterned heterostructure scheme comprising a nanodot chain (NDC) layer and a skyrmion nano-racetrack layer for precise monitoring of skyrmion motion. By exploiting the stray field generated by the moving skyrmion within the racetrack layer, magnetization changes are induced in nanodots within the NDC layer. These changes then translate into high-frequency magnetization oscillation signals that encode valuable information about the dynamic characteristics of driven skyrmions, such as speed and acceleration of the skyrmion, either by spin waves or spin currents. This scheme holds great potential for advancing spintronic devices based on a profound understanding of skyrmion dynamics.

Driving skyrmions in flow regime in synthetic ferrimagnets

The last decade has seen significant improvements in our understanding of skyrmions current induced dynamics, along with their room temperature stabilization, however, the impact of local material inhomogeneities still remains an issue that impedes reaching the regime of steady state motion of these spin textures. Here, we study the spin-torque driven motion of skyrmions in synthetic ferrimagnetic multilayers with the aim of achieving high mobility and reduced skyrmion Hall effect. We consider Pt|Co|Tb multilayers of various thicknesses with antiferromagnetic coupling between the Co and Tb magnetization. The increase of Tb thickness in the multilayers reduces the total magnetic moment and increases the spin-orbit torques allowing to reach velocities up to 400 ms−1 for skyrmions with diameters of about 160 nm. We demonstrate that due to reduced skyrmion Hall effect combined with the edge repulsion of the magnetic track, the skyrmions move along the track without any transverse deflection. Further, by comparing the field-induced domain wall motion and current-induced skyrmion motion, we demonstrate that the skyrmions at the largest current densities present all the characteristics of a dynamical flow regime.

Energy-efficient synthetic antiferromagnetic skyrmion-based artificial neuronal device

Magnetic skyrmions offer unique characteristics such as nanoscale size, particle-like behavior, topological stability, and low depinning current density. These properties make them promising candidates for next-generation spintronics-based memory and neuromorphic computing. However, one of their distinctive features is their tendency to deviate from the direction of the applied driving force that may lead to the skyrmion annihilation at the edge of nanotrack during skyrmion motion, known as the skyrmion Hall effect (SkHE). To overcome this problem, synthetic antiferromagnetic (SAF) skyrmions that having bilayer coupling effect allows them to follow a straight path by nullifying SkHE making them alternative for ferromagnetic (FM) counterpart. This study proposes an integrate-and-fire (IF) artificial neuron model based on SAF skyrmions with asymmetric wedge-shaped nanotrack having self-sustainability of skyrmion numbers at the device window. The model leverages inter-skyrmion repulsion to replicate the IF mechanism of biological neuron. The device threshold, determined by the maximum number of pinned skyrmions at the device window, can be adjusted by tuning the current density applied to the nanotrack. Neuronal spikes occur when initial skyrmion reaches the detection unit after surpassing the device window by the accumulation of repulsive force that result in reduction of the device’s contriving current results to design of high energy efficient for neuromorphic computing. Furthermore, work implements a binarized neuronal network accelerator using proposed IF neuron and SAF-SOT-MRAM based synaptic devices for national institute of standards and technology database image classification. The presented approach achieves significantly higher energy efficiency compared to existing technologies like SRAM and STT-MRAM, with improvements of 2.31x and 1.36x, respectively. The presented accelerator achieves 1.42x and 1.07x higher throughput efficiency per Watt as compared to conventional SRAM and STT-MRAM based designs.

Rotational motion of skyrmion driven by optical vortex in frustrated magnets

Effective control of skyrmion rotation is of significant importance in designing skyrmion-based nano-oscillators. In this work, we numerically study the optical vortex-driven skyrmion rotation in frustrated magnets using the Landau–Lifshitz–Gilbert simulations. The skyrmion rotation is induced by the orbital angular momentum (OAM) transfer from the optical vortex to the skyrmion, which is regardless of the sign of the OAM quantum number m due to the helicity degree of freedom of the frustrated skyrmion. This property highly broadens the parameter range of the optical vortex in controlling the skyrmion rotation. The direction of the rotation is determined by the sign of m, and the radius and angular velocity depend on the magnitude of m, light polarization, and intensity. Interestingly, the helicity oscillation induced by the linearly polarized beam is much slower than that driven by the circularly polarized beam with a same intensity, resulting in a faster rotation of the skyrmion. This phenomenon demonstrates the advantage of the linearly polarized beam in controlling the dynamics of the frustrated skyrmion, benefiting energy-saving and high-efficient device design.

Skyrmions Subtractor Based on Dzyaloshinskii-Moriya Interaction Gate.

Skyrmions are increasingly favored in developing various spintronic devices as efficient information carriers. The proposed voltage-controlled Dzyaloshinskii-Moriya interaction (VCDM) offers an additional means to manipulate the movement of skyrmions. In this study, we investigated how the skyrmions behave when passing through the VCDM gate in ferromagnetic nanotracks driven by current. Our findings suggest that reducing the strength of the Dzyaloshinskii-Moriya interaction (DMI) can more effectively block skyrmions, while increasing the DMI strength can more effectively attract them. This indicates that the motion behavior of skyrmions can be controlled by changing the shape of the VCDM gate, thereby demonstrating the effectiveness of VCDM gates in controlling skyrmion motion. Due to the ability of VCDM gates to block skyrmions, we have designed a robust subtractor based on skyrmions. These results provide valuable insights for the development of future skyrmion-based devices using the DMI method.

Steady motion of 80-nm-size skyrmions in a 100-nm-wide track

The current-driven movement of magnetic skyrmions along a nanostripe is essential for the advancement and functionality of a new category of spintronic devices resembling racetracks. Despite extensive research into skyrmion dynamics, experimental verification of current-induced motion of ultra-small skyrmions within an ultrathin nanostripe is still pending. Here, we unveil the motion of individual 80 nm-size skyrmions in an FeGe track with an ultrathin width of 100 nm. The skyrmions can move steadily along the track over a broad range of current densities by using controlled pulse durations of as low as 2 ns. The potential landscape, arising from the magnetic edge twists in such a geometrically confined system, introduces skyrmion inertia and ensures efficient motion with a vanishing skyrmion Hall angle. Our results showcase the steady motion of skyrmions in an ultrathin track, offering a practical pathway for implementing skyrmion-based spintronic devices.

Skyrmion motion induced by spin-waves on magnetic nanotubes

Abstract We investigate the skyrmion motion driven by spin waves on magnetic nanotubes through micromagnetic simulations. Our key results include demonstrating the stability and enhanced mobility of skyrmions on the edgeless nanotube geometry, which prevents destruction at boundaries — a common issue in planar geometries. We explore the influence of the damping coefficient, amplitude, and frequency of microwaves on skyrmion dynamics, revealing a non-uniform velocity profile characterized by acceleration and deceleration phases. Our results show that the skyrmion Hall effect is significantly modulated on nanotubes compared to planar models, with specific dependencies on the spin-wave parameters. These findings provide insights into skyrmion manipulation for spintronic applications, highlighting the potential for high-speed and efficient information transport in magnonic devices.

Asymmetric energy barrier induced magnetic skyrmion diodes in synthetic antiferromagnetic nanotracks

Magnetic skyrmions are nanoscale spin textures with topological protection properties, which are regarded as promising information carriers. When skyrmions move along nanotracks, their trajectories will shift if affected by skyrmion Hall effect and pinning effect. In this work, the influence of trapezoidal notches in synthetic antiferromagnetic nanotracks on the dynamics of skyrmions is investigated through micromagnetic simulation. The results exhibit that the asymmetric energy barrier induced by the asymmetric geometric structure can hinder reverse motion of skyrmions to realize the unidirectional conduction function of the diodes. Adjusting the height and inclination angle of the trapezoidal notch can effectively expand the current operating windows of the diodes, and the larger the height or inclination angle, the higher the threshold current density to overcome the pinning effect of the geometric energy barrier. Furthermore, the failure mode has a crucial impact on the implementation of skyrmion diodes. By utilizing the asymmetric structure, the forward conduction and reverse cutoff of skyrmion-based diodes can be achieved within 4 ns, with lower energy consumption than traditional diodes, resulting in high efficiency and low energy consumption of diodes. This work proposes a method for realizing the diode functionality by simply altering the geometric structure of the nanotracks, which may play an important role in the design and application of skyrmion-based diodes.

Manipulation of hybrid skyrmion dynamics by step Dzyaloshinskii–Moriya interaction approach

The topological protected magnetic state, which plays a pivotal role against any continuous deformation of a magnetic skyrmion, comes with an unwanted skyrmion Hall effect (SkHE) that poses a significant challenge in practical applications. Here, we present a detailed micromagnetic simulation study that delves into the controlled manipulation of skyrmion dynamics through subtle engineering of the Dzyaloshinskii–Moriya interaction (DMI) in a hybrid skyrmion-based racetrack. In particular, we introduce a gradient variation of bulk and interfacial DMIs, which results in a parabolic trajectory of the skyrmion motion, thereby allowing us to find a critical DMI ratio with almost zero SkHE. Most importantly, we present a novel approach involving the engineering of a racetrack with strategically placed step DMI regions that gives us meticulous control over the size and speed of the hybrid skyrmions. The present study gives a new direction for the simultaneous realization of stable skyrmions without SkHE and an increased skyrmion speed with optimized DMI engineering.

Multi-terminal logic transmission via orthogonal currents controlling magnetic skyrmion motion in a perpendicular ferromagnetic multilayer nanotrack

Magnetic skyrmions are topologically nontrivial whirling spin textures with great potential for next-generation magnetic logic and memory applications as spintronic information carriers. The abilities to precisely manipulate skyrmion generation and motion using electric current are considered to be important issues for developing the high-efficiency skyrmion-based devices. In this paper, a skyrmionic logic device structure is proposed to realize the generation of Néel-type skyrmions from the topologically trivial domains. Micromagnetic simulations are employed to investigate the controllable skyrmion motions manipulated by the orthogonal current excitations in a perpendicular ferromagnetic multilayer nanotrack. The transversal skyrmion motion induced by the skyrmion Hall effect is balanced through introducing a y-axial current. A three-terminals logic output is achieved by adjusting the strength of currents along x and y directions. The interlayer coupling effect for stabilizing skyrmion nucleation is finely tuned via a ferromagnetic pinning layer in absent of the external magnetic field. It is found that both the perpendicular magnetic anisotropy and the Dzyaloshinskii-Moriya interaction are critical for the formation of stabilized skyrmions. The controllable skyrmion motion and multi-terminal information transmission offer a novel path for designing skyrmion-based logic and memory devices.

Designing and Constructing a Skyrmion Diode Device via Antiferromagnetic Exchange Bias Engineering

AbstractMagnetic skyrmions are topologically protected spin textures with nanoscale dimensions. They hold great promises as the building blocks for new generations of racetrack memories and computing devices due to their prominent properties. However, skyrmionic devices fabricated within the framework of conventional lithography usually suffer from magnetic disorders at material boundaries where spin disorders can easily pin and destroy magnetic skyrmions. In the present work, a new paradigm is demonstrated that enables the precise patterning and control of micro‐scale skyrmion bubble devices using the domain walls rather than the physical boundaries of the material. Such a paradigm patterns the background magnetic domain to stage the skyrmion motion, which is precise, reconfigurable, nondestructive, and can resolve the conventional issues introduced by disorders. This paradigm is demonstrated by implementing a skyrmion diode using a precisely patterned asymmetric racetrack defined by magnetic domains. The interaction between a moving skyrmion and the staging domain walls is well understood by both skyrmion motion experiments and micromagnetic simulations. Such a new paradigm serves as a crucial foundation for device applications of magnetic skyrmions in general.

Scalable Low‐Power Skyrmionic Logic Gate Library

AbstractMagnetic skyrmions, despite being promising ultra‐low energy information carriers with wide bandwidth and nonvolatility, are not used for any universal scalable logic system. Here, a detailed understanding of skyrmion motion in nanowires under different geometries and drive conditions is established. Then, these insights are used to introduce a general Boolean‐universal gate block system with components, emulation, and simulation algorithms. The resulting system can collectively form a scalable, cascadable, and universal skyrmion logic system and produce arbitrary logic designs. The NOR, AND, OR, NAND, XNOR, and FULL ADDER gates are provided here as example demonstrations of the system. The toolkit lays the foundation for bridging the gap between theoretical exploration and practical implementation of skyrmion‐based computing. The skyrmion block components may help reduce energy consumption per logic operation after eliminating Joule heating. The insights and designs may help skyrmions be used in state‐of‐the‐art electronic design automation.

Fast current-induced skyrmion motion in synthetic antiferromagnets.

Magnetic skyrmions are topological magnetic textures that hold great promise as nanoscale bits of information in memory and logic devices. Although room-temperature ferromagnetic skyrmions and their current-induced manipulation have been demonstrated, their velocity has been limited to about 100 meters per second. In addition, their dynamics are perturbed by the skyrmion Hall effect, a motion transverse to the current direction caused by the skyrmion topological charge. Here, we show that skyrmions in compensated synthetic antiferromagnets can be moved by current along the current direction at velocities of up to 900 meters per second. This can be explained by the cancellation of the net topological charge leading to a vanishing skyrmion Hall effect. Our results open an important path toward the realization of logic and memory devices based on the fast manipulation of skyrmions in tracks.

Skyrmion Motion in Ferrimagnets Driven by Magnetic Anisotropy Gradient

The topological skyrmions in ferrimagnet systems provide new opportunities to investigate the fundamental spin dynamics. Effective manipulation of ferrimagnet skyrmion motion is a vital task for future spintronics applications, motivating intense research on magnetization dynamics with voltage as driving sources. In this work, the skyrmion in ferrimagnets driven by voltage controlled magnetic anisotropy gradients, which tends to move toward the low anisotropy area and has a constant velocity, is investigated. Thiele's theory analysis is reported on the velocities of the skyrmion dependencies on the anisotropy gradient, the net angular momentum density, and the damping coefficient, which are confirmed nicely by the atomistic simulations. It is demonstrated that the velocity of the skyrmion reaches to a maximum value at a nonzero net angular momentum density δs different from the domain wall, and the Hall angle of ferrimagnet skyrmions can be controlled by δs. The results are useful for the understanding of ferrimagnet skyrmion dynamics and may open an alternative way for the design of ferrimagnet spintronic devices.

Acoustic-driven magnetic skyrmion motion.

Magnetic skyrmions have great potential for developing novel spintronic devices. The electrical manipulation of skyrmions has mainly relied on current-induced spin-orbit torques. Recently, it was suggested that the skyrmions could be more efficiently manipulated by surface acoustic waves (SAWs), an elastic wave that can couple with magnetic moment via the magnetoelastic effect. Here, by designing on-chip piezoelectric transducers that produce propagating SAW pulses, we experimentally demonstrate the directional motion of Néel-type skyrmions in Ta/CoFeB/MgO/Ta multilayers. We find that the shear horizontal wave effectively drives the motion of skyrmions, whereas the elastic wave with longitudinal and shear vertical displacements (Rayleigh wave) cannot produce the motion of skyrmions. A longitudinal motion along the SAW propagation direction and a transverse motion due to topological charge are simultaneously observed and further confirmed by our micromagnetic simulations. This work demonstrates that acoustic waves could be another promising approach for manipulating skyrmions, which could offer new opportunities for ultra-low power skyrmionics.

Direct Observation of Room-Temperature Magnetic Skyrmion Motion Driven by Ultra-Low Current Density in Van Der Waals Ferromagnets.

The recent discovery of room-temperature ferromagnetism in 2D van der Waals (vdW) materials, such as Fe3GaTe2 (FGaT), has garnered significant interest in offering a robust platform for 2D spintronic applications. Various fundamental operations essential for the realization of 2D spintronics devices are experimentally confirmed using these materials at room temperature, such as current-induced magnetization switching or tunneling magnetoresistance. Nevertheless, the potential applications of magnetic skyrmions in FGaT systems at room temperature remain unexplored. In this work, the current-induced generation of magnetic skyrmions in FGaT flakes employing high-resolution magnetic transmission soft X-ray microscopy is introduced, supported by a feasible mechanism based on thermal effects. Furthermore, direct observation of the current-induced magnetic skyrmion motion at room temperature in FGaT flakes is presented with ultra-low threshold current density. This work highlights the potential of FGaT as a foundation for room-temperature-operating 2D skyrmion device applications.

Controllable arrangement of magnetic skyrmions by strain regulation

The efficient manipulation of magnetic skyrmions is crucial for the development of future spintronic devices. Here, we demonstrate the controllable arrangement of magnetic skyrmions through strain regulation in the bilayer film system composed of piezoelectric and ferromagnetic layers. The motion characteristics and energy distribution of skyrmions in the ferromagnetic layer under an in-plane periodic strain with a sinusoidal shape are investigated by using a phase-field model. It is found that the final equilibrium location of the skyrmion with the lowest total energy has the maximum positive strain and a zero strain gradient. Furthermore, the periodic strain transforms the disordered multi-skyrmions to an ordered skyrmion array at the desired positions by adjusting the wavelength and amplitude of the strain. Based on the controllability of the skyrmion position, the temperature gradient perpendicular to the strain leads to the directional motion of multi-skyrmions along the desired track. The controllable directional motion of skyrmions by strain regulation proposed in this work is promising for application in the racetrack memory and neuromorphic computing devices.

Collective variable model for the dynamics of liquid crystal skyrmions

Liquid crystal skyrmions are topologically protected spatially-localized distortions of the director field which exhibit particle-like properties including translational motion in oscillating electric fields. Here, we develop a collective variable model of the skyrmion dynamics, extending the approach of Long and Selinger proposed earlier for one dimensional systems. The model relates the skyrmion motion to a complex dynamics of the width of the twist wall around the skyrmion core. The width evolves in a non-reciprocal way, quantifying squirming deformations of the high twist region within on and off states of the field. We analyze in details the average skyrmion velocity as a function of the frequency and strength of the field as well as its duty cycle. The model predictions agrees qualitatively with experiments and results of numerical minimization of the Frank-Oseen model. Our results provide insights into the conditions necessary to observe velocity reversal as a function of the field parameters.

Quantifying the polar skyrmion motion barrier in an oxide heterostructure

Exotic polar topologies such as polar skyrmions have been widely observed in the ferroelectric superlattice system. The dynamic motion of the polar skyrmion under external forces holds promise for applications...