Dresden 2009 – scientific programme
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MA: Fachverband Magnetismus
MA 19: Micro Magnetism / Computational Magnetism
MA 19.10: Talk
Wednesday, March 25, 2009, 12:30–12:45, HSZ 403
Chiral symmetry breaking in magnetic vortices due to sample roughness. — •Arne Vansteenkiste1, Bartel Van Waeyenberge2, Markus Weigand2, Michael Curcic2, Hermann Stoll2, and Gisela Schutz2 — 1Ghent University, Gent, Belgium — 2Max Planck Institute for Metals Research, Stuttgart, Germany
An asymmetry between magnetic vortices with core polarizations up and down has been experimentally observed for square and disk-shaped nanostructures. E.g., different vortex core switching threshold excitations were measured, which was unexpected since the two core polarizations in these structures should behave perfectly symmetric. It was suggested that, e.g., surface roughness might cause the symmetry breaking, but it remained unclear if a small roughness could cause such a large asymmetry.
We have investigated the symmetry breaking with a new 3D finite-element micromagnetic package, which is specifically designed to handle non-perfect thin-film structures. The package uses a modified fast multipole method to calculate magnetostatic fields efficiently, without breaking the intrinsic symmetry of the sample, and employs a dynamically adaptive mesh to speed-up the calculations.
Our simulations confirm that a small roughness can indeed cause a large symmetry breaking between the two vortex core polarizations. The asymmetry can be explained by the lack of mirror-symmetry of the rough thin-film structures. The local character of the roughness causes a strong coupling with the vortex core and consequently a large asymmetry.