Nonlinear dynamics of magnetic vortices in Spin-Torque Nano-Oscillators
(2025)
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- Authors
- Supervisors
- Abreu Araujo, Flavio
- Abstract
- In this thesis, the nonlinear dynamics of magnetic vortices in spin-torque nano-oscillators are investigated. These devices, which are nanoscale dc-to-ac converters, rely on magnetic tunnel junctions for which the free layer exhibits a nonuniform vortex state. When subjected to an injected current, sustained precessions of the vortex core may occur, generating an oscillatory output signal through magnetoresistance effects. In this work, we enhance the Thiele equation by improving the magnetostatic and Zeeman terms, the latter arising from the Ampère-Oersted field (AOF). These modifications reveal a clear chirality-dependent splitting of the dynamics, validated through micromagnetic simulations. We then introduce a method to extract the vortex stiffness directly from micromagnetic data. This method highlights discrepancies between analytical expressions and simulations. To refine our predictions, we develop a quantitative model incorporating the vortex core position dependence of the gyrotropic and damping terms. Our data-driven Thiele equation approach achieves up to eight orders of magnitude faster computation than micromagnetism, while maintaining equivalent accuracy. It precisely reproduces both transient and steady-state dynamics. Furthermore, our findings reveal a unique dynamical regime for larger-diameter junctions, for which the vortex core is confined between two orbits. Finally, we examine a system consisting of a pair of oscillators in close proximity, focusing on the AOF influence rather than well-known synchronization through dipolar interactions.
- Affiliations
Citations
de Wergifosse, S. (2025). Nonlinear dynamics of magnetic vortices in Spin-Torque Nano-Oscillators.