Ralph F. Simmons

Media design for user density of up to 3 bits per pulse width

It is noted that increasing the user density in digital recording by the use of linear equalization and sequence detection will provide new design opportunities and new constraints on the recording media. The authors have evaluated five head/media designs to determine how the media can benefit from systems operating at higher user density. They conclude that the limits to recording at high user density are nonlinearities in dibit amplitude and increases in the dibit amplitude jitter and correlation. The origins of the nonlinearities and noise are described by knockdown and recoil of the media magnetization. Head/media systems must be designed to avoid knockdown. The systems which will be the most successful in taking advantage of new channel techniques will be system using high-efficiency codes with multiple bits per flux change. >

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. >

Noise correlations in dibit recording

Medium noise correlations in dibit data patterns have been studied experimentally in thin film disk/head recording systems. An empirical eigenfunction expansion was utilized to identify the dominant noise modes and possible associated physical mechanisms. At large bit separation where noise power adds linearly, dibit in‐phase jitter and out‐of‐phase jitter were found to be the leading noise modes. The noise waveform shape associated with out‐of‐phase jitter approaches that of the dibit signals (i.e., this mode of noise becomes amplitude‐like) as the bit separation is reduced. In addition, dibit amplitude variation due to the interaction between the two pulses generates the same amplitude‐like noise for a small dibit separation. Amplitude mode noise increases as the bit separation is reduced, causing the supralinear noise increase in high recording density. Results from nonlinear amplitude reduction measurement in dibit recording indicate a close correlation between the nonlinearities and the supralinear noise enhancement at high recording density.

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.

Design and peak shift characterization of magnetoresistive head thin film media system

The design, fabrication and peak shift characterization of a thin film head-thin film media system capable of recording at 19.4 Kbits/mm2(12.5 Mbits/in2) are described. The thin film media uses a magnetic layer of a sputter deposited alloy of Co having coercivity of 600 Oe. The thin film head is a single-turn-inductive write, barber-pole-biased magnetoresistive read head. This combination of read and write technologies reduces step coverage problems and simplifies the fabrication of the thin film head. A high resolution interval counter was used to measure the peak shift due to intersymbol interference and, hence, provide the information necessary for a focus-on-peak-shift design. The results of peak shift measurements for different gap length heads are reported. It has been found that the time interval between adjacent peaks varies with each write process, but once the transitions are recorded, the write process variations appear as a fixed peak shift for a given peak. This peak shift does not affect the error rate in the same statistical sense as random noise does.

PREDICTION OF THE LIMITATIONS PLACED ON MAGNETORESISTIVE HEAD SERVO SYSTEMS BY TRACK EDGE WRITING FOR VARIOUS POLE TIP GEOMETRIES

The typical configuration for inductive write/magnetoresistive read heads used in hard disk applications involves a shared pole (shield) between the write transducer and the read transducer. The shared pole forms the leading pole of the write portion of the head. The write track width is primarily determined by the width of the trailing pole, however, the leading pole geometry has an important influence on track‐edge writing effects and, therefore, on embedded servo system performance. This effect is simulated for shared pole, trimmed pole, and, for comparison, conventional inductive head pole geometries. The merits of each geometry and impact of side writing on servo is discussed.

Across-the-track performance of dual stripe magnetoresistive heads

Advances in 3D simulations of magnetoresistive heads and media are combined to permit detailed analysis of track-edge recording effects in hard disk applications. Vector Preisach models for thin film media were combined together with 3D micro-magnetic models of dual stripe heads into a single simulation system. This has permitted prediction of servo gain non-linearities in dual stripe heads used in embedded servo disk drives. The models are used to determine the impact of linewidth and alignment tolerances on servo gain nonlinearity.

MR head manufacturing sensitivity analysis using transmission line model

Transmission line based equations are developed to describe the operation of MR heads. An analytical solution for magnetic flux in MR films is derived for linear operation. This transmission line method is used to analyze the design center of shielded dual stripe, soft adjacent layer and barberpole MR heads. Error propagation analysis is used to analyze the manufacturing tolerance sensitivity of these various heads. Finally, a Monte Carlo simulation is used to investigate the expected distribution in performance of manufactured MR heads. >

Vector combined preisach model with a biaxial switching operator for simulation of unoriented thin-film media

Abstract The elements of a vector Preisach model for unoriented thin-film media are described. The implementation consists of adding a biaxial anisotropy switching function to the classic Preisach algorithm. The model was developed to simulate high-squareness thin-film recording media. The utility of the model is demonstrated by the simulations of the usual VSM curves: the major loop, forward and reverse remanence loops, and the δM curve, as well as the response to rotating fields. These results are compared with experimental measurements made on an unoriented thin-film hard disk material.