Hardayal S. Gill

A magnetoresistive gradiometer for detection of perpendicularly recorded magnetic transitions

A magnetoresistive gradiometer to detect perpendicularly recorded transitions has been conceived. It utilizes two parallel magnetoresistive stripes with opposing sense/bias currents. The magnetoresistive elements mutually bias each other with the same polarity bias fields. The fields of a perpendicular transition centered between the two stripes increase the resistance of one stripe while decreasing that of the other, therefore providing maximum output signal using differential detection. The detector provides a Lorenztian‐type readback waveform and rejection of common‐mode noise. The experimental readback waveform exhibited a pulse width at half maximum of 0.7 μm for a head flying at 0.2 μm above the media surface.

Bias scheme analysis of shielded MR heads for rigid disk recording

Biasing schemes for MR heads for use at high areal densities, O(108 bits/in.2), longitudinal recording, are reviewed. By use of the finite element analysis, a number of important design parameters are examined including the transfer function and the peak shift for each biasing scheme. We show that the roll‐off peak shift and linearity characteristics are dependent on the type of bias scheme.

Determination of overwrite specification in thin-film head/disk systems

A self-consistent write analysis using the Preisach model is presented and used to calculate overwrite in thin-film head/disk systems. Two overwrite characterization procedures are discussed, and for each of the procedures the calculated values are compared with measurements. Through a correlation of overwrite, nonlinear peak shifts, and readback output voltage the authors determine the overwrite requirement. They show that whereas -30 dB of overwrite will ensure a satisfactory overall performance of the recording system, a much lower overwrite, say -20 dB, can work in certain situations. An analytical implementation of the self-consistent model is presented and verified with measurements. The analytical approach can be used to determine the overwrite at any applied field for any head/disk combination. The authors introduce a normalized effective field h/sub n/, which depends on M/sub r/ delta , H/sub c/, and other head/disk parameters. It is shown that a value of h/sub n/ greater than 0.8 is needed for overwrite values of better than 25 dB. The importance of various head/disk parameters in optimizing the overwrite is also discussed. >

Effect of sense current on Barkhausen noise in magnetoresistive recording heads

The currents in the contact leads of a magnetoresistive (MR) head produce fields that influence the behavior of the underlying MR element. In the conventional lead configuration the current enters and leaves the MR element on the same side of the MR element. In the region where the conductor overlaps the MR element a field is produced that has a component that is along the easy axis of the MR element. The direction of this longitudinal field is in opposite directions on either side of the track and this destabilizes the MR element. Barkhausen noise results from the multidomain states that are produced. If instead the leads are configured to be on either side of the element the longitudinal fields are in the same direction and a single‐domain state is stabilized. Results are presented that demonstrate the dependence of the hysteresis on the current. Kerr microscope measurements are shown that illustrate the behavior of the magnetization in the elements.

Measured fields and performance of recording heads

A method is presented for obtaining the longitudinal magnetic field produced by recording heads. The method entails the use of a microloop to directly measure the perpendicular field Hy across the gap region of the head and the calculation of the longitudinal field Hx using a transform of Hy(x). This method has been applied to the study of narrow‐track, thin‐film heads. The ability to predict the shape of the readback waveform from a measurement of the head field is demonstrated.

Head field measurements in three dimensions

A method is described for obtaining all three components of the field produced by a magnetic recording head. The perpendicular component of the field, H/sub y/, is measured in the plane of the air-bearing surface, and from this the three components, H/sub x/, H/sub y/, and H/sub z/, are calculated in the region below the surface. An example is presented of the field distribution for a thin-film head, and a comparison is made with both analytic and three-dimensional finite-element calculations. >

Stray field sensitivity of a pole head on a dual layer perpendicular disk

The two-dimensional finite element method is used to study the effects of external fields on single-pole heads on a dual-layer medium. Profiles of the perpendicular field, H/sub y/, under the pole tips are given for various geometries and field directions. A 1000* scale model was built to study the three-dimensional effects for external y-axis fields. The stray field problem is shown to be serious for y-axis fields, i.e. fields perpendicular to the disk surface. >

Shielded MR gradiometer read pulse shape for perpendicular medium

Isolated output pulse shapes are calculated for magnetoresistive gradiometer read heads having various geometric and magnetic parameters. The two‐dimensional finite‐element and reciprocity methods are used. The ferromagnetic shield has a big effect on the pulse shape, especially for closely spaces shields. High shield reluctance causes pulse broadening and large positive tails. Addition of a medium underlayer decreases the pulse undershoots and increases pulse amplitude. A reluctance model is given that explains most of the observed effects on pulse shapes and illustrates the importance of reluctance balance to achieve optimum pulse shape.