Longitudinal thin-film rigid disk media with an overlying high permeability, low coercivity "keeper" layer is shown to improve inductive head performance beyond the limit of contact recording. Data taken with a Read-Rite tripad pseudo-contact inductive thin-film head shows that the keeper layer improves peak-detector channel margin by 25% and reduces soft error rate by 6 orders of magnitude. The keeper layer improves system signal to noise ratio by 3dB to 6dB, and reduces PW-50 from 0.292pm (11.5pin) to 0.228pm (9.0pin). A fly height study shows that the keeper layer allows an additional 25nm (lpin) higher flying height than standard media for equivalent channel margin or soft error rates.A model, treating the keeper layer as a magnetic parametric amplifier is proposed. Calculations show that the keeper layer modulates the inductance of the tripad head by 25 nano-Henrys, or about 5% of the total inductance.
Abstruct -The magnetic effects of a saturable magnetic keeper layer on the peak amplitude and shape of isolated readback pulses from longitudinal thin film media were modeled as 2-dimensional magnetostatic field interactions using the boundary element method. The model assumes a standard thin film head and fly height of a 50% slider, a saturable NiFe keeper, and a perfectly sharp recorded transition in highcapacity longitudinal thin film media.Isolated pulses calculated from the model show that the keeper increases the peak amplitude(55%), decreases the half-height pulse width(46%), introduces pulse shape asymmetry, and eliminates undershoots from pole edges. The pulse shape is found to be very sensitive to-changes in both-the head-bias current and the head-disk spacing. ' Fig. 1 Flux from a single transition through the thin film head.
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