Thermal Decay of a Single Néel Skyrmion via Helicity Slip in a Nanodisk

Abstract

Dynamics of the decay of a single skyrmion confined in a ferromagnetic nanodisk in the presence of stochastic thermal noise are studied using micromagnetic simulations. By analyzing the time‐varying oscillations of the in‐plane and out‐of‐plane magnetization under the influence of the thermal field, the presence of two skyrmion eigenmodes with frequencies differing by an order of magnitude is identified—a low‐frequency mode associated with gyration of skyrmion core and a high‐frequency breathing mode associated with the oscillations of the skyrmion radius. It is shown that the thermal fluctuations not only affect the topological charge but also the helicity of the skyrmion, changing the helicity to oscillate around ±π/4—a value which is in between that of the Néel skyrmion and a vortex. A phenomenon of helicity slip between +π/4 and −π/4 is revealed due to the thermal fluctuations. The helicity slip is explained based on an energy barrier that arises due to a combination of thermally induced deformations of skyrmion and the finite size of the disk.