Spin Dynamics of Magnetic Disks in the Vortex State

Spin dynamics of magnetic disks in the vortex state is studied by ultrafast optics. In patterned Co disks, we found that time-domain spin dynamics are strongly dictated by the transient field direction. For transient field directions applied parallel to the disk plane, an azimuthal spin-wave mode splitting of Co disks of greater than 2 GHz arises on account of the presence of the vortex core. In the NiFe/Cu/Co disks, even though the laser beam only probes the top NiFe disks, we observe that there exists a dominant high frequency resonance close to that of Co disks. This is due to the dynamic dipolar interaction between the Co and NiFe layers. Spin dynamics in a large array of NiFe disks also has been studied through examination of the time-resolved magneto-optical Kerr effect at diffraction spots.