Time-resolved imaging of the gyration dynamics of nπ states in weak PMA systems

Despite the numerous predictions from micromagnetic simulations [1], only limited experimental investigations of the dynamical processes of perpendicularly magnetized spin configurations, such as e.g. magnetic skyrmions [2,3] exist. One of the causes behind this is the relatively high Gilbert damping (e.g. for Pt/Co stacks on the order of 0.2 [4]), and to the relatively high density of pinning sites of the typical materials employed for the stabilization of such magnetic states. Such high values of both pinning and Gilbert damping strongly influence the behavior of the perpendicularly magnetized spin configurations both statically [5] and dynamically [3]. In this contribution, we present an alternative solution to the use of multilayer stacks exhibiting perpendicular magnetic anisotropy (PMA) for the time-resolved investigation of the dynamical processes of magnetic skyrmions and the more complex nπ states. This solution relies on the use of a Permalloy-based PMA system exhibiting a weak PMA [6]. By judiciously optimizing the sample design, we were able to stabilize magnetic configurations ranging from magnetic skyrmions to more complex nπ states (see Fig. 1) in nano- structured elements. The nπ states stabilized in the nanostructured elements were excited by RF and pulsed magnetic fields generated through the injection of electrical currents across a tailored antenna fabricated close to the magnetic nanostructures. Thanks to the combination of a low Gilbert damping and a relatively low density of pinning sites of this weakly-PMA system, the gyration dynamics in magnetic states ranging from magnetic skyrmions to the more complex nπ states could be imaged by time-resolved scanning transmission x-ray microscopy, proving the feasibility of this material for the study of the dynamical processes in magnetic skyrmions and in nπ states.