MICROSCOPIC INVESTIGATIONS OF OVERWRITTEN DATA

The magnetic field distributions of overwritten patterns on rigid thin film disk media have been imaged with submicron resolution by using the magnetic force scanning tunneling microscope. The capability of the device to measure fields locally is exploited to quantitatively understand the conditions under which portions of overwritten data can remain and be detectable. The persistence and retrievability of previously recorded data are related to the radial offset of the head during overwrite for patterns created at high and low recording densities. It is observed that at high densities, for offsets less than 2 mum, overwritten transitions affect the newly written patterns by inducing track width modulation along its edges. At low densities, the track width variations are less noticeable, but can be elucidated by examining the detailed geometrical structure of overwritten patterns.