Dependence of anisotropy and damping on shape and aspect ratio in micron sized Ni81 Fe19 elements

We have studied magnetic anisotropy and damping in Ni81Fe19 elements of different shape and aspect ratio by time-resolved scanning Kerr effect microscopy and micromagnetic simulations. Square elements show a fourfold anisotropy that becomes weaker with increasing aspect ratio. Square elements with aspect ratio <230 show an anisotropy of the apparent damping that becomes stronger with decreasing aspect ratio. Variations in the apparent damping may be understood in terms of dephasing of spin wave modes that leads to the appearance of fringes in time-resolved magnetic images.