Shape-dependent anisotropy and damping of picosecond magnetisation dynamics in a micron sized Ni81Fe19 element

We have observed a four-fold variation of the anisotropy and damping of the magnetisation precession in a square Ni81Fe19 element of 10 μm length by time-resolved scanning Kerr-effect microscopy. The measured frequencies are interpreted with the aid of a coherent rotation model, while micromagnetic modelling is used to understand the dynamic magnetic images and hence the variation of the damping.