Optical detection of vortex spin-wave eigenmodes in microstructured ferromagnetic disks

We examine the excitation of spin-wave eigenmodes in the vortex state of microsized ferromagnetic circular dots made of Permalloy (Ni81Fe19) both theoretically and experimentally using Brillouin light scattering microscopy. We report on the detection of the radial spin-wave eigenmodes of single elements with high mode number (up to n = 13 for the largest disk radius 2.5 mu m). Theoretically we obtain an equation for the eigenfrequencies valid for arbitrary dot aspect ratios (thickness/radius) within the magnetostatic approximation. We demonstrate the influence of the disk radius on the spatial mode profiles, in particular, changes in the pinning of the dynamical magnetization at the edges and in the center of the disks. The measured spin-wave eigenfrequencies are in good agreement with our calculations for the disks with different radii.