Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy

Abstract

Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin–orbit torques, can be reliably tuned by changing the magnitude of spin–orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin–orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic applications in the future.

Individual skyrmion manipulation by local magnetic field gradients

“…Typical systems investigated utilise Co or CoFeB as magnetic films and Pt as heavy metal layer, while either an oxide or another heavy metal are used as top layers. In these material stacks, current pulses are usually employed to drive skyrmion motion, exploiting the spin Hall effect in the heavy metal layer and consequent spin-orbit torque [16][17][18][19] . However, despite the low values of depinning currents required, fast skyrmion motion is only attainable using large current densities, which are accompanied by undesired Joule heating effects.…”

Magnetic skyrmion bubble motion driven by surface acoustic waves

“…Note that the skyrmion bubble mass becomes smaller in the presence of Dzyaloshinskii-Moriya interactions which will introduce some changes in the dynamics. 48,49 See supplementary material for the details of skyrmion bubble mass estimation.…”

Walker Breakdown with a Twist: Dynamics of Multilayer Domain Walls and Skyrmions Driven by Spin-Orbit Torque

“…This breakdown occurs when certain (Bloch-like) layers reach a critical velocity, beyond which precession sets in, leading to an oscillatory trajectory and a diminished mobility. For typical material parameters, this velocity is of the order of tens of m/s, corresponding to the velocity range in recent experiments [21,[45][46][47][48]. The breakdown originates from the interplay of SOT, DMI, and magnetostatic interactions [42], thanks to which DWs in some layers can be driven toward a Bloch configuration amenable to precession (because of the surface-volume stray field interactions [42]) while others maintain a Néel (or tran-sient [49]) character.…”