&Cartridge; physics 14, s90
Adding a friction term to models helps them take better account of how spin textures develop experimentally at room temperature.
Spin system models typically treat vortex-like spin configurations called skyrmions as quasiparticles whose motion follows a gyroscopic pattern. But the predictions of the equation currently used to describe such motions – Thiele’s equation – do not agree with experimental observations on the motion of skyrmions and other spin textures. Markus Weißenhofer and his colleagues from the University of Konstanz are now solving this problem by adding an additional friction term to Thiele’s equation.
The Thiele equation was established in the 1970s as an equation of motion for individual Skyrmionic quasiparticles. It successfully describes both current-driven movements and Brownian movements of skyrmions at low temperatures and high damping. However, the equation fails at high temperatures and low attenuation.
In their simulations, Weißenhofer and his colleagues carried out numerical simulations to investigate the influence of spin damping in a metallic thin film. They found that at finite temperatures, spin waves called magnons occur, which dampen the movement of the skyrmions already present in the film. By adding a friction term to the Thiele equation to account for this damping, the team found that their updated equation of motion successfully describes experimental results. The size of the new term increases linearly with temperature and is independent of other forms of damping as well as the size of the skyrmion.
The researchers say their result provides a simple framework to better predict the dynamics of spin textures. This framework could be useful for experimenters when incorporating skyrmions into spintronics technologies such as energy storage.
Rachel Berkowitz is Corresponding Editor for physics based in Vancouver, Canada.
- M. Weissenhofer et al., “Skyrmion dynamics at finite temperatures: Beyond the Thiele equation”, Phys. Rev. Lett.127, 047203 (2021).