Modal spectrum of permalloy disks excited by in-plane magnetic fields

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.