RESEARCH PROJECTS

Antiferromagnetic Skyrmions: Manipulating spin textures by electric and spin currents is one of the main challenges in the field of spintronics. Ferromagnetic skyrmions recently attract a lot of attention because they are small and not pinned as easily as domain walls when driven by electric currents. Meanwhile, ferromagnetic skyrmions have disadvantages as well, such as the presence of stray fields and transverse motion, making them harder to employ in spintronic devices. In this work, we propose a novel topological object: the antiferromagnetic (AFM) skyrmion and explore its properties analytically and by micromagnetic simulations. This topological texture has no stray fields, see Fig. 1 (a-b), and is more mobile than its ferromagnetic analogue.

We find that the Dzyaloshinskii-Moriya interaction, which comes from relativistic spin-orbit effects and generally favors spin spiral structures, stabilizes AFM skyrmions. The AFM skyrmion radius depends on the strength of the Dzyaloshinskii-Moriya interaction and temperature. Moreover, the thermal properties, e.g. such as the radius and diffusion constant, differ from those of ferromagnetic skyrmions. Due to the unusual topology, the AFM skyrmions do not feel a transverse (Magnus) force and therefore do not move transverse to an applied current, which makes them interesting candidates for spintronic applications [Phys. Rev. Lett. 116, 147203 (2016)]. These results can be understood in terms of a generalized Thiele equation [Phys. Rev. Lett. 110, 127208 (2013)], which describes soft modes of the skyrmion motion. This equation shows an exact cancellation of the Magnus force due to the presence of two AFM sublattices with opposite topological charges. It also leads to a larger diffusion constant of the AFM skyrmion as compared to its ferromagnetic counterpart.

Domain walls in nanotubes with Dzyaloshinskii-Moriya interaction: We presented an analytic study of domain-wall statics and dynamics in ferromagnetic nanotubes with spin-orbit-induced Dzyaloshinskii-Moriya interaction (DMI).

Even at the level of statics, dramatic effects arise from the interplay of space curvature and DMI: the domains become chirally twisted leading to more compact domain walls. The dynamics of these chiral structures exhibits several interesting features. Under weak applied currents, they propagate without distortion. The dynamical response is further enriched by the application of an external magnetic field: the domain wall velocity becomes chirality-dependent and can be significantly increased by varying the DMI [Physical Review B 93, 054418 (2016)]. These characteristics allow for enhanced control of domain wall motion in nanotubes with DMI, increasing their potential as information carriers in future logic and storage devices.