Greg S. Mowry

Noise in high performance thin-film longitudinal magnetic recording media

The problem of noise in thin-film longitudinal media is analyzed experimentally and theoretically. The physical mechanism for the noise is shown to be fluctuations in the geometry of the zig-zag transitions separating bit cells. The shifted-transition noise model is introduced as a means of quantifying the noise processes. Spatial, spectral, and autocorrelation properties are introduced. A calculation of the RMS noise voltage yields the characteristic noise versus density curves found experimentally, and clarifies their interpretation with respect to the signal-to-noise ratio. The corresponding experimental data for several plated and sputtered media are presented and analyzed in the light of the model predictions.

Measurement of the intrinsic signal‐to‐noise ratio for high‐performance rigid recording media

Electrical measurements of the intrinsic media signal‐to‐noise ratio are made to examine the future impact of increasing recording density. Intrinsic media signal‐to‐noise measurements are made on oxide, on several thin‐film‐plated and sputtered longitudinal media, and on sputtered CoCr vertical media. Integrated spectrum noise versus write frequency and performance data are presented and contrasted for the different media. The character of the oxide and vertical media noise are shown to be produced by a uniformly distributed source whereas the noise of the thin‐film longitudinal media is shown to be caused by localized fluctuations in the zig‐zag transition region.

Thin-film magnetoresistive heads for narrow-track Winchester applications

The characteristics of a thin-film magnetoresistive head for narrow track Winchester applications are presented and contrasted to those for a comparable thin-film inductive head. Emphasis is placed upon establishing the repeatibility of the magnetoresistive head output and the unique characteristics associated with a write-wide/read-narrow transducer in a narrow-track environment. Off-track overwrite and cross-talk measurements as well as saturation and density measurements are presented for longitudinal recording on thin-film metal media. The suitability of the parametrics (including second harmonic produced peakshift) for high areal density recording is discussed. Finally, the potential of using a MR head in connection with vertical recording media is explored from the standpoint of output, density, and overwrite.

Permanent magnet stabilization of an overlaid MR head

Higher area density in the rigid disk magnetic recording industry is being achieved with magneto-resistive (MR) heads biased with a soft adjacent layer (SAL). The abutted and the overlaid designs are the two approaches most commonly used. Reader stability is a result of a single domain structure due to boundary control stabilization (BCS) from exchange or magnetostatic coupling. The details of a particular design determine on track and off track performance. Recent reviews and products suggest that the magnetostatically coupled abutted head design is superior to published overlaid designs. This paper describes the electrical performance and physical characteristics of another overlaid design that performs on track and off track at the recording density of 650 Mb/in/sup 2/.

Origin of microtrack side bumps for a shared pole MR head on isotropic media

MFM observations on oriented and isotropic media are used to identify the source of side bumps seen for microtrack profiles written with a shared pole MR head. The effect is shown to arise from side writing and the orientation of the medium. MFM results for a pole-trimmed writer are also presented and the side-writing effect is shown to be diminished on isotropic media.

The effect of a magnetic underlayer on the magnetic properties of plated Permalloy (abstract)

The effects of a magnetic underlayer on the magnetic behavior of overlayer/underlayer combinations were investigated. Permalloy underlayers of 100 nm thickness and composition 82% Ni‐18% Fe by weight were sputter deposited on 3‐in.‐diam Si substrates. Magnetic orientations of the underlayers were set at 0°, 45°, and 90° with respect to the orientation of a subsequently plated Permalloy (79%Ni‐21%Fe overlayer. Several film combinations were generated on each of the various underlayer configurations with plated thicknesses ranging from 0.1 to 2.0 μm. Spatial maps of magnetic orientation and Hk for underlayers and underlayer/overlayer combinations were collected using a modified Kerr BH imager (Kerr BHI) designed from Gudeman.1 The maps covered a 5 cm×5 cm square region with 5 mm spacing between points. Comparison of the maps before and after plating shows a partial reduction in the measured Hk values for film systems with large underlayer/overlayer orientation differences. A uniform decline in the effect of...

Measurement of intrinsic signal to noise ratios for high performance rigid recording media (abstract)

Measurement of the noise spectrum of high performance oxide, thin‐film longitudinal and perpendicular rigid recording media have been made in order to establish the frequency dependence of the noise, the intrinsic media signal‐to‐noise ratio, and the practical recording density limit set by error rate considerations. For the oxide media tested, the noise spectrum was flat with frequency at 0.7 μV rms/100 μV rms signal indicating it was close to the particle size determined noise limit. For plated Co‐P and sputtered Co‐Re thin‐film longitudinal media the noise spectrum increases with frequency. At D70 (18 KFCI) the noise was 1.25 and 1 μV per 100 μV rms signal, respectively. For the vertical media the noise contribution came from shouldering around the fundamental frequency and was 2.5 μV/10 μV rms signal at D70 (22 KFCI) and increased with frequency. The measurements were made with both inductive and magnetoresistive heads (improved sensitivity) at 900 TPI and over a 20‐MHz bandwidth. D70 for the oxide me...