Role of Local Gyrotropic Force in Antiferromagnetic Skyrmion Deformations

Past numerical studies have reported that antiferromagnetic skyrmions (AFMSks) exhibit elliptical deformations while in motion, followed by a full breakdown at a critical limiting velocity. The skyrmion equilibrium structure, as well as the limiting velocity have been shown to depend on several material parameters, namely, Heisenberg exchange, magnetic anisotropy and Dzyaloshinskii–Moriya interaction (DMI). However, the deformation mechanism in AFMSks has not yet been understood. In this work, the dynamics of skyrmions in antiferromagnetic (AFM) materials are studied utilizing atomistic simulations performed in the VAMPIRE software. It is well known that the total Magnus force acting on a skyrmion in a fully compensated AFM is zero, thus, its center of mass is not deflected. Here, using numerical simulations over a large range of material parameters, we demonstrate that the distortions and critical behavior are due to a local imbalance of the gyrotropic force which emerges when the AFMSk is in motion. We propose that this differential force is balanced by the restoring force acting to maintain skyrmion energy. Our model is consistent with numerical simulation data and provides a qualitative physical explanation of the deformation mechanism. These results not only expand the understanding of fundamental properties of magnetic skyrmions, but are significant for the understanding of AFMSks and their subsequent use in the field of spintronics.