Abstract
The creation and annihilation of magnetic vortex–antivortex pairs has been predicted to have a role in magnetic switching in permalloy nanostructures, but has never previously been observed. High-speed X-ray microscopy now enables the evolution and dynamics of this process to be studied in detail. Magnetic thin-film square- or disc-shaped nanostructures with adequate dimensions exhibit a magnetic vortex state: the magnetization vectors lie in the film plane and curl around the structure centre. At the very centre of the vortex, a small, stable core exists where the magnetization points either up or down1,2. The discovery of an easy core reversal mechanism3 did not only open the possibility of using such systems as magnetic memories, but also initiated the fundamental investigation of the core switching mechanism itself4,5,6,7,8,9,10,11,12,13,14,15. Theoretical modelling predicted that the reversal is mediated by the creation and annihilation of a vortex–antivortex pair3,4,16, but experimental support has been lacking until now. We used high-resolution time-resolved magnetic X-ray microscopy to experimentally reveal the first step of the reversal process: the dynamic deformation of the vortex core. In addition, we have measured a critical vortex velocity above which reversal must occur5,17. Both observations support the previously proposed reversal mechanism.
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