Current-Induced Dynamics and Instability Pathways of Skyrmioniums in Chiral Magnets

TL;DR

This study explores the current-driven behavior, instabilities, and collective dynamics of skyrmioniums in chiral magnets, revealing their unique Hall effect and various transformation pathways under different conditions.

Contribution

It provides a comprehensive analysis combining simulations and theory to understand skyrmionium dynamics, including their nonequilibrium responses and collective behaviors.

Findings

Skyrmioniums exhibit a finite transverse velocity despite zero topological charge.

Current-induced deformations enhance the skyrmionium Hall effect, making it comparable to skyrmions.

Distinct instabilities such as elongation, collapse, and stripe formation occur at high currents depending on magnetic parameters.

Abstract

We present a comprehensive study of current-driven dynamics, transformations, and instabilities of skyrmioniums in chiral magnetic films, considering both isolated objects and collective states forming skyrmionium-based meta-matter. Using micromagnetic simulations combined with an analytical description based on the generalized Thiele equation, we clarify how the internal structure of skyrmioniums governs their nonequilibrium response to electric currents. Despite having zero total topological charge, skyrmioniums exhibit a finite transverse velocity under applied currents. We show that this skyrmionium Hall effect originates from an imbalance between positive and negative topological contributions of the inner skyrmion and surrounding ring, which typically occupy different areas. Current-induced deformations further enhance this imbalance, yielding Hall angles comparable to those of skyrmions. At higher current densities, skyrmioniums undergo distinct instabilities depending on magnetic field and uniaxial anisotropy, including elongation, collapse into a skyrmion, transformation into a topologically trivial droplet, and expansion into stripe textures. We map these regimes in current--field and current--anisotropy phase diagrams and resolve their microscopic pathways via the evolution of topological charge and local rotational measures. Beyond isolated textures, mixed skyrmion--skyrmionium lattices display rich collective dynamics, including elastic transport, polymorphic transitions, soliton exchange, and stripe formation. Pulsed currents provide additional control, enabling access to regimes beyond continuous driving. Our results establish skyrmioniums and their meta-matter as tunable nonequilibrium systems probing the topological energy landscape far from equilibrium.