The stability of recorded magnetization on hard disk drives (HDDs) is influenced by external environments, such as temperature and magnetic fields. Small scratches are frequently formed on an HDD medium surface on contact with the magnetic head. The influence of a perpendicular magnetic field and mechanical scratching on the magnetization structural stability of perpendicular recording media was investigated by using a magnetic force microscope. The magnetization structure started to change at lower magnetic fields in an area near and below mechanical scratches when compared with normal areas with no scratches. A quantitative analysis of variations in the magnetization structure was carried out by taking into consideration the difference in MFM images observed for the same sample area before and after exposing the sample to different magnetic fields.