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MA: Fachverband Magnetismus

MA 33: Non-Skyrmonic Magnetic Textures I

MA 33.13: Vortrag

Donnerstag, 20. März 2025, 12:45–13:00, H16

Lifetime of toroidal Hopfions in bulk magnets with competing exchange interactions — •Moritz Sallermann^1,3, Hannes Jonsson³, and Stefan Blügel^1,2 — ¹RWTH Aachen University, Germany — ²PGI-1, Forschungszentrum Jülich, Germany — ³University of Iceland, Iceland

Hopfions are three-dimensional topological solitons characterized by the Hopf invariant, which quantifies the pairwise linking number of constant magnetization pre-images. In simple models of bulk magnets with competing exchange interactions, Hopfions emerge as local energy minima in numerical simulations. However, to fully understand their stability against decay due to thermal fluctuations, merely identifying these local minima is insufficient. A more comprehensive understanding requires determining their expected average lifetimes. We employ the harmonic transition state theory framework, a computationally efficient yet approximate method, to estimate these lifetimes. This approach yields an Arrhenius-type expression comprising two key ingredients: the energy barrier and an entropic prefactor. The energy barrier represents the minimal energy needed to initiate decay, while the entropic prefactor measures the relative entropy of the energy bottleneck, compared to the configuration space volume of the local minimum. We present our findings on the lifetimes of Hopfions in these systems and discuss technical challenges encountered, such as the treatment of Goldstone modes and the computation of sparse positive-definite determinants.

We acknowledge funding from the ERC grant "3D MAGIC".

Keywords: Hopfion; Lifetime; Energy barrier; Harmonic transition state theory; Atomistic spin models