Magnetization reversal processes in perpendicular anisotropy thin films observed with magnetic force microscopy

We have carried out studies of the magnetic reversal process of a rare earth–transition metal thin film with perpendicular magnetic anisotropy using a magnetic force microscope (MFM) capable of applying in situ magnetic fields. The magnetization of the microscopic area shown in MFM images was determined for a number of field values comprising a complete hysteresis loop. This microscopic hysteresis loop was found to be nearly identical to a bulk hysteresis loop. Changes in the magnetization of the film as the hysteresis loop was traversed can be linked to individual microscopic domain changes evident in the MFM images. These studies show that the magnetization of this film was characterized by a two-stage process – fast and slow rates of change of magnetization with applied field. A second experiment in which the film was incompletely saturated and brought back to zero field showed that domain nucleation was not responsible for the rate of the fast process, but rather all magnetization changes were primarily limited by the low domain wall mobility. These observations are linked to previous work on magnetization processes in similar magnetic systems.