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MA: Fachverband Magnetismus

MA 30: Skyrmions II

MA 30.3: Vortrag

Mittwoch, 20. März 2024, 15:45–16:00, EB 301

The dynamics of Skyrmion shrinking — •Frederik Austrup1, Wolfgang Häusler2, Michael Lau1, and Michael Thorwart11I. Institut für Theoretische Physik, Universität Hamburg — 2Institute of Physics, University of Augsburg

It is generally accepted that Skyrmions shrink in size before they decay when unstable. We present numerical studies to identify values for the external parameters, including the applied magnetic field and the Dzyaloshinskii-Moriya interaction strength, stabilizing Skyrmions in two-dimensional ferromagnets. Further, we follow their time evolution in the unstable cases, for different lattice constants and in the presence of Gilbert damping. Contrary to the commonly expected simply exponentially decreasing size we find a more complicated time dependence. The time evolution of the Skyrmion radius ρ0 can be divided into three phases: ρ0(t) starts decreasing quadratically in time before it continues according to an exponential law over a certain period of time. However, before reaching a time tc, a behavior consistent with a square root decay, ∼ (ttc)1/2, is found. Analytically, we derive a differential equation for ρ0(t) from the Landau-Lifshitz-Gilbert equation for the time-dependent topological charge density, utilizing a Skyrmion profile of triangular shape. Solving this equation, we find indeed a shrinking behaviour nicely following the observed exponential law that crosses over into a square root decay pattern. The time tc is found to depend on Zeeman-field and on exchange field strengths, and on the initial Skyrmion size.

Keywords: Skyrmion; Ferromagnet; Skyrmion Decay; Skyrmion Collapse; Skyrmion Shrinking

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