arXiv subjects

R. Sbiaa

Publications and source records attributed to R. Sbiaa.

8 recordsLinked to original sources

arXiv2026

Confinement-controlled pathways to complex skyrmionic textures in Co/W/Pt multilayers

Magnetic skyrmions and higher-order topological spin textures offer rich opportunities for multi-level information encoding, yet their deterministic stabilization and transformation under geometric confinement at room temperature remain poorly understood. Here, we demonstrate that geometric confinement acts as a robust and universal control parameter that governs a hierarchical transformation pathway of chiral spin textures in Pt/Co/W multilayer micro-tracks. As the confinement increases, extended labyrinth domains fragment into isolated skyrmions, followed by the systematic suppression of skyrmion pairs and the preferential stabilization of compact higher-order textures. We find that confinement strongly enhances the formation of skyrmioniums via recombination and promotes their subsequent evolution into uniform skyrmion bags by capturing additional skyrmions. Statistical analysis reveals a confinement-driven redistribution of topological populations, with skyrmion bags emerging as the dominant state in the narrowest tracks. Supported by micromagnetic simulations, our results establish geometric confinement as a deterministic selector of complex topological textures and reveal a previously unexplored route for engineering higher-order skyrmionic states at room temperature. These findings provide a scalable materials strategy for multistate skyrmion-based spintronic and memory architectures.

physics.app-ph↗

arXiv2026

Stabilized biskyrmion states in annealed CoFeB bilayer with different interfaces

This study investigates the stability of skyrmions and biskyrmions in perpendicular magnetic tunneling junctions with a thick CoFeB/Ta/CoFeB free layer. The samples showed a magnetoresistance of ~ 41% when annealed at 230 °C. Magnetic force microscopy revealed the existence of skyrmions and biskyrmions at room temperature in the as-deposited state and under an external magnetic field. Annealing at 330 °C enhanced interfacial Dzyaloshinskii-Moriya interaction (DMI) and crystallinity, enabling the spontaneous coexistence of these topological structures. Micromagnetic simulations using MuMax3 explored the interplay between DMI strength, sign, and skyrmion chirality. Skyrmions exhibited repulsive interactions, while biskyrmions displayed attractive interactions due to the difference in helicities. The study highlights the influence of multilayer structure and varying Ta layer thicknesses on the DMI charility, which modulates the formation of complex spin textures. These results provide an understanding of skyrmion and biskyrmion dynamics and their potential for spintronic applications, including racetrack memory and data storage technologies.

cond-mat.mtrl-sci↗

arXiv2025

Interaction-Induced Spiral Motion and Breathing Dynamics of Neel Skyrmions in Ferromagnetic Thin Films

Magnetic skyrmions exhibit particle-like stability and rich dynamical behaviour arising from their topological nature, making them promising building blocks for future spintronic devices. In this work, we investigate the interaction dynamics of two Neel-type skyrmions in an ultrathin ferromagnetic film through a combined analytical and numerical approach. Full micromagnetic simulations reveal that when the initial separation exceeds twice the skyrmion radius, the pair undergoes a repulsive interaction leading to an outward spiral trajectory whose radial and angular components depend sensitively on the Gilbert damping, consistent with particle-like models of skyrmion motion. The simulations further show a two-component oscillatory behaviour in the out-of-plane magnetization: a fast intrinsic breathing mode superimposed on a slower interaction-induced modulation. Using Thiele collective-coordinate model, an expression for the radial drift, angular decay, and logarithmic growth of the separation distance is derived. The analytical predictions show excellent agreement with numerical results, confirming the exponential form of the long-range interaction potential. A continuum micromagnetic analysis of the skyrmion tail explains the origin of the exponential decay and its role in governing the interaction strength. Together, these findings provide a unified framework for understanding spiral motion, breathing dynamics, and long-range repulsion in interacting skyrmion systems, offering insights relevant for multi-skyrmion information carriers and collective skyrmion-based devices.

physics.app-ph↗

arXiv2024

Plasmon-driven creation of magnetic topological structures

In the present research, we demonstrate the usage of plasmonic effects in thin film structures to control magnetic topological textures, specifically skyrmions and skyrmioniums. We investigate numerically the generation and alteration of these topological structures caused by hemisphere gold nanoparticle placed over a magnetic layer coated with a dielectric material. The electromagnetic and photothermal models are used to clarify the processes of producing heat and absorption, and the results were implemented in micromagnetic formalism to reveal the dynamics of magnetization under various conditions. Our findings demonstrate the significance of the laser pulse duration and the contact area between nanoparticles and the underlying magnetic layer in forming topological textures. In particular, we show how to generate a single skyrmion, multiple skyrmions, and skyrmioniums, and how to dynamically transition between these states. These results highlight the possibility of manipulating magnetic textures by using plasmonic effects, which presents significant opportunities for spintronics and non-conventional computer applications.

physics.app-ph↗

arXiv2023

Dynamics of interacting skyrmions in magnetic nano-track

Controlling multiple skyrmions in nanowires is important for their implementation in racetrack memory or neuromorphic computing. Here, we report on the dynamical behavior of two interacting skyrmions in confined devices with a comparison to a single skyrmion case. Although the two skyrmions shrink near the edges and follow a helical path, their behavior is different. Because the leading skyrmion is between the edge and the trailing one, its size is reduced further and collapses at a lower current density compared to the single skyrmion case. For higher current density, both skyrmions are annihilated with a core-collapse mechanism for the leading one followed by a bubble-collapse mechanism for the trailing one.

physics.app-ph↗

arXiv2023

Stabilizing skyrmions in stepped magnetic devices for multistate memory

The dynamics and stability of magnetic skyrmions within a nano-track with multiple confinements are investigated. Firstly, the motion of a single skyrmion under spin transfer torque (STT) is studied. By accurately adjusting the current pulse magnitude and width, the study reveals the possibility to pin and stabilize the skyrmion in each confinement. Due to the Hall angle, the depining of the skyrmion from the top confinement requires two pulses with adjustable time delay while a single pulse is enough to depin it for the case of bottom confinement. In the case of two skyrmions, once one is pinned in one confinement, the second one stabilizes in the nearest available empty state and no more than one skyrmion could be seen in single confinement. Finally and for further confirmation of this behavior, the motion of a large number of skyrmions is investigated under the same conditions. The results show that a multistate device could be obtained with still the existence of only one skyrmion per state. The skyrmions could be displaced along the nano-track until their annihilation at the end of the device.

physics.app-ph↗

arXiv2020

Domain wall dynamics in stepped magnetic nanowire with perpendicular magnetic anisotropy

Micromagnetic simulation is carried out to investigate the current-driven domain wall (DW) in a nanowire with perpendicular magnetic anisotropy (PMA). A stepped nanowire is proposed to pin DW and achieve high information storage capacity based on multi-bit per cell scheme. The DW speed is found to increase for thicker and narrower nanowires. For depinning DW from the stepped region, the current density Jdep is investigated with emphasis on device geometry and materials intrinsic properties. The Jdep could be analytically determined as a function of the nanocontriction dimension and the thickness of the nanowire. Furthermore, Jdep is found to exponential dependent on the anisotropy energy and saturation magnetization, offering thus more flexibility in adjusting the writing current for memory applications.

cond-mat.mes-hall↗

arXiv2019

Controlled spin-torque driven domain wall motion using staggered magnetic nanowires

The growing demand for storage, due to big data applications, cannot be met by hard disk drives. Domain wall (DW) memory devices such as racetrack memory offer an alternative route to achieve high capacity storage. In DW memory, control of domain wall positions and their motion using spin-transfer torque are important challenges. In this paper, we demonstrate controlled domain wall motion using spin-transfer torque in staggered magnetic nanowires. The devices, fabricated using electron-beam lithography, were tested using a magneto-optical Kerr microscopy and electrical transport measurements. The depinning current, pinning potential and thermal stability were found to depend on the device dimensions of the staggering nanowires. Thus, the proposed staggering configuration helps to fine-tune the properties of domain wall devices for memory applications.

physics.app-ph↗