Performance of U-Pole Writers With Straighter Field Contours

Curvature of transitions recorded onto a magnetic disc has become more pronounced as tracks narrow. Curvature creates interference between adjacent transitions recorded at high bit density, and broadens the read back signal pulse. Curved transitions have a shape similar to that of the field contours that write them. A concave write pole trailing surface, or “U-pole”, pushes the field contours near the pole edges farther down track. This straightens the contours by partially compensating for transition curvature. We used a track trimming technique to compare transition curvature of flat poles and U-poles, and verified that the U-pole reduced curvature by more than 30%. We also demonstrated that the more curved transitions written by flat poles generate ~ 1 nm more pulse broadening at the track edge relative to those written by U-poles. However, modeling predicts a ~ 10% loss in down track field gradient near the center of a U-pole. Measurements of bit error rate across the track confirm the corresponding loss in U-pole performance relative to a flat pole over all but the outer portions of a track.