Magnetization Dynamics investigated by X-Ray Microscopy

Magnetic micro-objects and their dynamics have attracted considerable attention recently. When excited by either a short (~100ps) magnetic field pulse [1,2], or by a high frequency (>100MHz) sine wave [3] it is possible to investigate various excitations of the magnetization in such thin film structures[4]. Depending on the size and geometry these objects contain either only a single magnetic domain, or a pattern consisting of several domains separated by domain walls and by vortices or antivortices.
We combine time resolved x-ray microscopy experiments with micro-magnetic simulations to gain insight into the dynamics of such objects and into the coupling between the various excitations.
We start with simple discs or squares, where three modes connected to the homogenously magnetized domains, the domain walls and the vortex exist. From there we move to more complex objects. For instance, in a rectangular platelet a configuration containing a stable combination of vortices and an antivortex can be created. Such a single cross-tie wall can be understood as being a coupled micromagnetic system with three static solitons. We report on its magnetization dynamics including the vortex-antivortex interactions. The spectrum of eigenmodes is investigated as well as the effect of different vortex core orientations. We show that the vortex dynamics can be used to identify the core configuration which is not directly accessible to x-ray microscopy because of its limited spatial resolution.

[1] J. Raabe et al., Phys. Rev. Lett. 94, 217204 (2005)
[2] M. Buess et al., Phys Rev. B 74, 100404 (2006)
[3] B. Van Waeyenberge et al., Nature 444, 461 (2006)
[4] R. Hertel et al., Phys. Rev. Lett. 97, 177202 (2006)