Ultrafast Magnetization Reversal Dynamics Investigated by Time Domain Imaging

Spatiotemporal magnetization reversal dynamics in a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ microstructure is studied using ps time scale scanning Kerr microscopy. Time domain images reveal a striking change in the reversal associated with the reduction in switching time when a transverse bias field is applied. Magnetization oscillations subsequent to reversal are observed at two resonance frequencies, which sensitively depend on the bias field strength. The oscillation at $f=2\mathrm{}$ GHz is caused by the damped precession of $\mathbf{M}$, while the lower frequency $\sim 0.8$ GHz mode is interpreted in terms of domain wall oscillation.