Magnetic force scanning tunneling microscope imaging of overwritten data

In most digital recording systems, previously recorded data is not erased but simply written over. The extent of erasure of old data is a complex process that depends upon the recording parameters such as record current, record gap, densities and media parameters including coercivity and hysteresis. In addition, insufficient overwrite can also result from inaccurate electromechanical positioning of the record head during the re-recording process. Slight misalignment of the new data track relative to the previously written track results in incomplete erasure of the previous data, and residual magnetization of the old data persists along the track edges. This could have considerable implications on performance, as well as, on current notions of complete data erasure. To investigate this, we have developed a magnetic force scanning tunneling microscope to image magnetization patterns with sub-micron resolution, and applied it to commercially obtained hard disk media containing rewritten tracks.