Direct Magnetic Domain Observation of Magnetization Reversal With Pre-Existing Nucleation Sites in Co/Pt Multilayer

Time-dependent magnetic domain patterns of Co/Pt multilayer with a perpendicular magnetic anisotropy has been directly observed by a magneto-optical Kerr microscopy. From our direct domain observation, it is revealed that, when a negative exposure field has been applied after positively saturating the film first, the number of pre-existing nucleation sites decreases as a strength and an applied time of the exposure field increase. It was also observed that pre-existing nucleation sites can speed up the magnetization reversal process by two orders of magnitude, where a strong correlation between the number of nucleation sites and the half-reversal time is found.