I. A. Beardsley

Self-consistent computer calculations for perpendicular magnetic recording

A comparison of perpendicular and longitudinal recording indicates that conventional heads are suitable for recording on high coercivity media having perpendicular magnetic anisotropy. At equal bit shift and head to disk separation perpendicular recording gives a factor of 2.5 increase in the linear density attained with media in use today.

Significance of delta M measurements in thin film media

Remanence measurements have been proposed as a means of estimating the amount of intergranular exchange present in thin-film recording media. A micromagnetic model is used to compute remanence curves starting from a DC-saturated state and an AC-erased state, for a range of media parameters. It is found that the amount of intergranular exchange is the most important parameter determining the difference delta M between these two curves; however, the interpretation is clouded somewhat by the effect of anisotropy and other parameters. >

Self‐consistent recording model for perpendicularly oriented media

We describe modifications to the fully two‐dimensional self‐consistent recording model which make it more applicable to perpendicularly oriented media such as cobalt chromium alloys. Writing and reading with a thin‐film head are modeled at a separation of 0.2 μm and results are compared with experiment.

Modeling the record process

The evolution of write process modeling for digital magnetic recording is described. Typically such modeling depends on the assumption of a continuous recording medium which can be represented by its bulk hysteretic properties. The development of a vector model for hysteresis is presented and its adequacy is discussed.

Reconstruction of the magnetization in a thin film by a combination of Lorentz microscopy and external field measurements

A combination of two measurements is shown to be sufficient to determine the magnetization in a thin film except for a constant out-of-plane component, under the condition that the magnetization is uniform through the thickness. The measurements consist of DPC (differential phase contrast) Lorentz microscopy, which measures the path integral of the in-plane B field, and some measurements of the out-of-plane component of H above and below the film, for example by Hall probe. Field measurements on one side only are sufficient if the magnetization is in-plane. The in-plane magnetization is decomposed into a divergence-free part and a part with zero component of curl perpendicular to the plane of the film. The DPC measurement directly yields the divergence-free component, and the curl-free as well as the out-of-plane parts are found from a deconvolution of the perpendicular field. Several examples are given, and the interpretation of the two magnetization components in terms of B and H provides a qualitative description of the physics. >

Effect of particle orientation on high density recording

Self-consistent computer calculations are used to investigate the effect of media orientation on digital recording. The vertical contribution to the readback pulse is found to roll off more slowly than the in-plane, hence vertically oriented and isotropic media have the highest amplitude at extremely high densities. A loop model is derived for media exhibiting cubic anisotropy. Results on the possible advantages of such a medium over isotropic media with uniaxial anisotroy are inconclusive.

The recording process in longitudinal particulate media

The magnetic recording process has been simulated for normal particulate longitudinal media. The mechanism of record optimization as well as the effects of demagnetization fields, record spacing, and record gap have been investigated. Results are presented in terms of recording spectra and vector plots of the magnetization of an isolated transition. A method of examining magnetization patterns is presented that gives physical insight into the phenomena. Interference effects that lead to high- and low-current spectral nulls are explained. >

Determination of thin film media model parameters using DPC imaging and torque measurements

A micromagnetic model consisting of coupled hexagonal grains has been used to investigate the remanent-state ripple structure, the expected torque, and the rotational hysteresis behavior of thin magnetic films. The parameters of the model are the anisotropy field, the magnetostatic coupling, and the phenomenological exchange coupling between grains. The scale of the ripple pattern as measured by Lorentz microscopy using the differential phase contrast imaging technique can be used to fix the model parameters unambiguously, under the assumption that the parameters have fixed single values. Experimental rotational hysteresis curves cannot by fitted in detail without assuming a fairly broad distribution of anisotropy fields. It should be possible, given both kinds of data on a single sample, to determine the exchange coupling and average anisotropy field as well as a distribution of anisotropy fields which fits the width of the rotational hysteresis curve. >

Three dimensional write model for magnetic recording

A three dimensional self-consistent write model is developed. Transitions are computed for infinite and finite pole tip narrow track heads on oriented and in-plane isotropic horizontal media. Magnetization patterns and readback on- and off-track are discussed.

Analysis of asymmetirc, deterministic bit shift errors in a hard disk file

An extensive statistical analysis of soft errors occurring in an IBM 3380 K hard-disk file has been made. About 90% of the errors was bitshift-induced involving a single bit. There was a high degree of early/late asymmetry. It is shown that decreasing system signal-to-noise ratio (S/N) increases the error rate, but reduces the early/late asymmetry. The repeatability of errors suggests that most errors happen at or near a media-direct site. Self-consistent write-process modeling, taking into account media defects, indicates bitshift and amplitude degradation commensurate with the experimental results. >