The mode spectrum of 4 micron sized ferromagnetic permalloy disks exhibiting a vortex structure in equilibrium is investigated in detail.
Normal modes accessible by in-plane field excitations are examined. By
means of spatially resolved techniques using Kerr microscopy we
recorded the modal structure of the disks at zero bias field. We
employed pulsed and continuous wave excitation. As a result we report
on normal modes up to the fifth order. Using inductive and spatially
resolved resonance measurements the evolution of the mode spectrum as a
function of an external magnetic field was investigated. Quantized
modes in longitudinal as well as in transverse direction in the uniform
magnetized disks were observed. Good agreement between the experimental
results and those from micromagnetic simulations was found.