Time-Resolved Imaging Reveals Transiently Chaotic Spin-Orbit-Torque-Driven Dynamics under Controlled Conditions

Spin-orbit torques (SOTs) act as efficient drivers for nanoscale magneticsystems, such as in magnetic tunnel junctions, nano-oscillators and racetrackgeometries. In particular, in combination with materials exhibiting highDzyaloshinskii–Moriya interaction, SOTs are considered to result inwell-controlled deterministic magnetisation dynamics and are, therefore, usedas robust drives to move and create magnetic skyrmions. In contrast to theseexpectations, we here find unpredictable, transiently chaotic dynamics inducedby SOT at an artificial anisotropy-engineered defect in a magnetic racetrack.Based on these controlled conditions, we directly observe the nanoscaledynamics with holography-based, time-resolved x-ray imaging. In concert withmicromagnetic simulations, we disclose a regime of violent picosecondfluctuations, including topological instabilities that, remarkably, result indeterministic final configurations. In addition, our images expose previouslyunseen skyrmion shedding and highlight the potential of transiently chaoticpathways for topological switching. Our approach offers new perspectives forthe investigation and application of highly non-linear SOT dynamics inspintronics materials.