Emergent Chaos-Like Dynamics of Spin-Orbit-Torque-Driven Magnetic Transitions.

Spin-orbit torques (SOTs) are widely used to control magnetization in nanoscale electric systems and are typically assumed to drive skyrmion nucleation and motion in a deterministic manner, especially in materials with strong Dzyaloshinskii-Moriya interaction. Here, using time-resolved holography-based x-ray microscopy supported by micromagnetic simulations, we reveal that on nano- to picosecond timescales the actual dynamics can deviate strikingly from this expectation by producing transient regimes of chaos-like behavior. By exploiting deterministic skyrmion generation at an anisotropy-engineered defect and implementing a high-resolution pump-probe scheme, we directly track the magnetization evolution in real space. This approach uncovers a dynamic phase transition that separates coherent SOT-driven motion from a regime of transient instability characterized by picosecond-scale fluctuations, strong domain disorder, topological instabilities, and skyrmion shedding, experimentally observed here for the first time. During SOT actuation, the system briefly enters this instability regime, showing short-lived chaos-like behavior, yet it reliably relaxes into robust and reproducible final states. Our results demonstrate a powerful methodology for accessing time-averaged nano- to picosecond dynamics in magnetic systems and reveal a previously hidden layer of transient, topologically rich behavior underlying nominally deterministic skyrmion control.