Miniature whirlpools of spins, also known as magnetic vortices, are currently a hot topic in magnetism research. In addition to providing insight into fundamental topological properties of materials, magnetic vortices show great potential as building blocks in advanced magnetic technologies. However, a completely reliable control over the vortex spin structure is mandatory before any such application can be realized. As current length scales in devices approach fundamental limits, stochastic (i.e. intrinsically random) processes will ultimately limit the performance of nanomagnetic devices. So far, most studies have assumed that thermal fluctuations are the only source for stochastic behavior.
A recent x-ray microscopy study at ALS Beamline 6.1.2 provided evidence that something else may be at work. In large arrays of asymmetrically shaped magnetic disks, it turns out that the ultrafast dynamics preceding vortex formation exhibits a characteristic chaotic behavior known as the butterfly effect, where minute changes can significantly determine the final outcome of a process. A collaboration of researchers from Berkeley Lab’s Materials Sciences Division, Korea, and Germany found that adjusting the interdisk distance can lead to fully deterministic behavior. The observed dependency on geometrical parameters cannot originate from thermal fluctuation effects, which are mainly determined by temperature.
The unique properties of soft x-ray microscopy at the ALS enable us to obtain a deeper fundamental understanding of nanoscale spin behavior, paving the way for potential applications harnessing unconventional spin structures.
Work performed on ALS Beamline 6.1.2.
Citation: M.-Y.Im, K.-S. Lee, A. Vogel, J.-I. Hong, G. Meier, and P. Fischer, “Stochastic formation of magnetic vortex structures in asymmetric disks triggered by chaotic dynamics,” Nature Communications 5, 5620 (2014).