Trochoidal dynamics and pair generation in skyrmion and antiskyrmion dynamics driven by spin-orbit torques

In a collaboration with colleagues at Johannes Gutenberg-Universität Mainz, Uppsala Universitet, and Christian-Albrechts-Universität zu Kiel, we have shown theoretically that skyrmions and antiskyrmions can behave very differently under spin-orbit torques. One key finding is that antiskyrmions can undergo trochoidal motion, which is analogous to Walker breakdown in domain wall dynamics. This threshold defines a speed limit for rectilinear displacement. Another is the onset of skrymion-antiskyrmion pair generation under large damping-like torques, which results in a gas with excess skyrmions. This imbalance in matter-antimatter production is a consequence of the asymmetric dynamics at high energies.

This work recently appeared in Nature Electronics.

Reference: U. Ritzmann, S. von Malottki, J.-V. Kim et al., Nat. Electron. 1, 451–457 (2018).

Imaging antiferromagnets with a single spin magnetometer

A consortium of research groups from the Universtié de Montpellier, Université Paris-Saclay, Universität Basel, CEA Saclay, and the Synchrotron SOLEIL has demonstrated the first real-space imaging of antiferromagnetic spin spirals in the multiferroic material bismuth iron oxide. The technique involves quantum sensing with a single spin magnetometer. A nice overview of this work can be found on the Oxitronics Group (UMPhy CNRS-Thales) website and on

Reference: I. Gross et al., Nature 549, 252–256 (2017).

Current-driven skyrmion dynamics in disordered films

Reference: J.-V. Kim and M.-W. Yoo, Appl. Phys. Lett. 110, 132404 (2017).

We studied how current-driven skyrmion motion in ultrathin films is affected by disorder. We modelled the disorder by assuming a grain structure, where the local perpendicular anisotropy fluctuates from grain to grain. We find that the velocity versus current curves are reminiscent of behavior in driven elastic interfaces in disordered media, such as domain wall creep. Moreover, we identify an extrinsic contribution to the skyrmion Hall effect due to disorder scattering, which is drive dependent. This work has just appeared in Applied Physics Letters.