Modeling and experimental results are presented for keepered longitudinal recording media and planar (undershoot-reduced) thin film recording heads with low flying heights for areal densities >1 Gb/in.2. The keeper layer is magnetically coupled to the medium magnetic transitions, reducing the transition demagnetization and narrowing the transition length by about 10% in the media after recording. The reproduced bias field and the transition fields combine in the keeper to produce a partially saturated region, thereby modifying the fields from the medium transitions at the head during playback. We present experimental data on the write and read process for keepered media. Boundary element model results are presented which explain the amplitude gain and pulse asymmetries observed experimentally. Use of a keepered medium allows areal density improvements >20% through higher bits per inch.
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.
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