The role of disk surface waviness on baseline instability of MR head

To investigate the role of disk surface waviness on the baseline instabilit y (BLI) of the read-back signals from MR head, we measured the average heig ht of surface waviness with a spatial wavelength of 0.4 to 5.0 mm using a w hite light interferometer instrument, We used an MR head over four sets of media to measure the baseline instability at OD and at MD. The results show that the baseline instability becomes worse as the surface waviness increa ses and that the baseline instability is linearly proportional to the surfa ce waviness. The result further shows that the effect of bias current on th e baseline instability is amplified on the disk with worse surface waviness . The surface waviness, therefore, can not be overlooked when evaluating th e media for a high-performance hard disk drive.