Magnetization reversal in ultrashort magnetic field pulses

Strong in-plane magnetic field pulses of 24.4 ps duration are used to study magnetization reversal in perpendicularly magnetized Co/Pt films. Ring domains, reminiscent of the field contour during exposure, are observed later with Kerr microscopy. Their radii represent switching fields which are in quantitative agreement with the coherent rotation model. The observation of intrinsic transition broadening is attributed to the existence of static and dynamic fluctuations of the magnetic anisotropy. © 1998 American Physical Society.