Tailed skyrmions -- an obscure branch of magnetic solitons

Abstract: 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.

• The paper reveals that tailed skyrmions, a novel magnetic soliton variant, emerge within a narrow external field range near the spin spiral to ferromagnetic phase transition.
• Researchers employed a 2D micromagnetic model and the geodesic nudged elastic band (GNEB) method to compute minimum energy paths and delineate stability regions.
• The findings provide actionable insights for spintronic applications and encourage further experimental studies on magnetic memory and logic devices using thermal dynamics.

Analysis of Tailed Skyrmions as a Subcategory of Magnetic Solitons

The study of magnetic skyrmions has been a crucial area in condensed matter physics due to their topological stability and potential applications in spintronic devices. In the research discussed here, the authors introduce a novel class of magnetic textures termed "tailed skyrmions" within the field of chiral magnets. These entities add complexity to the already diverse family of magnetic solitons and open potential new pathways for future investigations into magnetic phenomena.

Theoretical Framework and Methodology

The paper addresses a 2D micromagnetic model, focusing on energy contributions from Heisenberg exchange, Dzyaloshinskii-Moriya interaction (DMI), and magnetocrystalline anisotropy. The central objective is to identify and verify the existence and stability of tailed skyrmions, which manifest in a narrow band of external magnetic fields near the phase transition from spin spirals to saturated ferromagnetic states. Noteworthy in this analysis is the use of the geodesic nudged elastic band (GNEB) method to calculate minimum energy paths (MEP) and explore homotopies within solitons sharing identical topological charges.

Emergence and Characteristics

Tailed skyrmions exhibit an elongated morphology, differentiating them from their more well-known axially symmetric counterparts, such as $\pi$-skyrmions. The reported skyrmions appear in intricate morphologies—some akin to skyrmion bags, others featuring kinks and various topological charges, but with congruent topological transformation characteristics. Importantly, these formations are stabilized within certain anisotropy and external field parameters, delineated meticulously in the stability diagram provided by the study.

Computational Approach

For their simulations, the authors implemented various computational schemes, including energy minimization through Mumax3, Excalibur, and the Spirit code, to ensure the accuracy of stability ranges and the dynamics of tailed skyrmions. The study employs both finite difference and analytically derived methods to mitigate the effect of discretization and confirms its results through different computational models.

Implications and Future Directions

The discovery and characterization of tailed skyrmions suggest avenues for future work on both the theoretical and practical fronts. Theoretically, considerations around the energetic landscape reveal that traditional axially symmetric skyrmions likely remain the global energy minima within their classes. Nonetheless, the findings put forth the intriguing question of the second lowest energy configurations, highlighting the need for further study into configurations like $3\pi$-skyrmions or skyrmion bags and the conditions under which they stabilize.

Practically, this work envisions potential experimental applications, particularly within thermal fluctuation contexts, for generating tailed skyrmions from conventional skyrmions, thus providing a pathway to observational verification. Additionally, understanding the thermal dynamics and transitions of these complex structures may inform future technological developments within magnetic memory and logic devices.

Overall, the incorporation of tailed skyrmions into the larger categorization of magnetic solitons underscores the nuanced interactions of magnetic fields and material properties, with this research pushing boundaries and hinting at the complexities inherent in these remarkably stable configurations.