Abstract
The magnetization dynamics of a Ni81Fe19 disk of 16μm diameter and 50nm thickness was measured by time-resolved stroboscopic wide-field Kerr microscopy with a temporal resolution of less than 25ps. Time resolution is obtained by illumination with a frequency-doubled high-power Nd:YVO4 solid-state laser. The ground state of the magnetization is excited with a 700-ps-wide pulse of about 1.2kA∕m amplitude. After a fast rotation of magnetization and vortex displacement due to the pulsed magnetic field the magnetization slowly relaxes back to the ground state. During relaxation of the vortex we observe in the center of the element a stretched vortex structure that could be a 180° wall or a superposition of two vortices with switched core magnetization.
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