A disk drive is disclosed which demagnetizes the head after a write
operation. Write circuitry applies a write signal to the head in order to
write data to a selected data sector during a write operation, wherein
the write signal comprises a predetermined write current amplitude.
Control circuitry demagnetizes the head at the end of the write operation
by maintaining the write current amplitude while increasing a frequency
of an AC write signal applied to the head over a predetermined
demagnetization interval, wherein increasing the frequency of the AC
write signal decreases an amplitude of the AC write signal when observed
at the head.