Write induced track misregistration due to magnetic center shifts in thin film inductive heads

The effect of writing on track misregistration in thin film heads for hard disk drives is discussed. An experimental technique is presented which shows that writing causes changes in the magnetic state of the head. These magnetic changes are interpreted by the servo channel as shifts in the position of the head. Real track misregistration occurs as the servo tries to compensate. Typical variations in head position have a standard deviation of 2 to 4 microinches. From ontrack testing of a known unstable head it is concluded that unstable waveforms do not necessarily indicate a magnetic center shift. The opposite behavior has also been seen: magnetic center shifts occur with no noticeable change in waveform