Chaotic and relativistic dynamics of magnetic textures: Topology and applications in reservoir computing

PhD Program

Speaker

Javier Antonio Vélez Simanca

When

2025/12/05
11:00

Place

Assembly Hall of the Faculty of Psychology, EHU, Donostia/San Sebastián

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PhD Thesis defense by Javier Antonio Vélez Simanca

Supervisor: Rubén M. Otxoa, Kostyantyn Gusliyenko

Nonlinear Physics, Spintronics, and Condensed Matter Physics / Nonlinear magnetization dynamics, antiferromagnetic domain walls, spin–orbit torques, relativistic solitons, and functional dynamics for reservoir computing

This thesis investigates the nonlinear dynamics of magnetic textures in ferromagnetic, ferrimagnetic, and especially antiferromagnetic nanostructures, within a unified framework based on the Landau–Lifshitz–Gilbert equation. Tools from chaos theory are introduced to characterize periodic, quasiperiodic, and chaotic trajectories across different temporal scales. The studies include ferromagnetic nanoparticles, synthetic antiferromagnets driven by spin–orbit torques, and ferrimagnets excited by femtosecond laser pulses, revealing deterministic chaos and ultrafast magnetization reversal. The core of the work focuses on antiferromagnetic domain walls: 180° DWs exhibit relativistic chaotic proliferation under alternating spin–orbit fields, while for 90° DWs in Mn₂Au a relativistic variational model is developed that incorporates a continuously varying topological charge, accurately predicting both the velocity law and the Lorentz-like width contraction. Finally, the functional potential of these dynamics is demonstrated through a reservoir computing system based on AFM DWs, which achieves high efficiency, strong nonlinearity, and ultrafast operation. Overall, the thesis establishes a conceptual bridge between out-of-equilibrium magnetism, dynamical topology, and neuromorphic computation.