Hazel A. Shute

One-sided fluxes in planar, cylindrical, and spherical magnetized structures

In planar structures, magnetization patterns exist that have the surprising property that all the external fringing field of flux emerges from one side of the structure, with precisely none appearing on the other side. In the last 25 years, this fact has led to a number of useful applications. More recently, the same concept has been found to hold for both cylindrical and spherical hollow structures, where all the fringing flux emerges either inside or outside the structure, with precisely none appearing on the other side. Again, this has led to a number of important practical applications. While many of the concepts have been published previously, this paper contains, for the first time, a uniform mathematical analysis of these one-sided flux configurations. Additionally, the paper reviews the principal applications of one-sided flux structures.

Effect of island geometry on the replay signal in patterned media storage

In a move to extend the storage capabilities of magnetic storage systems beyond 1 Tb/in/sup 2/, the use of patterned media has often been cited. Here, recorded domains are constrained by the geometry of the magnetic island and not the geometry of the recording head. Conventional two-dimensional readout modeling techniques, using the reciprocity integral, rely on the assumption that the across-track medium magnetization is uniform under the giant magnetoresistive replay head. However, in the case of a geometrically constrained medium this is not the case. This work investigates the effect that the island geometry has on the characteristics of the replay signal in perpendicular patterned magnetic media storage through the extension of the reciprocity integral to three dimensions. The paper describes replay pulses that offer different characteristics from those obtained by conventional two-dimensional techniques. The origins of these differences are explained by the variation in medium magnetization across the track.

Approximate three-dimensional head fields for perpendicular magnetic recording

This paper proposes a method for obtaining approximate, but very accurate, three-dimensional (3-D) head fields for perpendicular magnetic recording heads. The method uses an assumed form for the scalar magnetic potential variation between a pole or shield and the underlayer to give the potential in the head/shields-face plane. It then uses this approximate air-bearing surface potential to find the potential or field components at any other position of interest. The approach is illustrated here by applying it to a symmetric double-shielded single-pole head with an underlayer and with side shields.

Accurate approximation of fields and spectral response functions for perpendicular recording heads

Solutions for the magnetic potential in rectangular regions with simple boundary conditions are used to approximate the two-dimensional potential in the head face plane of a recording head. This method of approximation can be applied to any recording head with rectangular corners, in the presence of an underlayer. The slot approximation is demonstrated for ring heads and shielded (magnetoresistive) pole heads. The quarter plane approximation is given for application to finite-length heads. Estimates of the field components and the spectral response function are derived from the approximate potential. The simple slot approximation is shown to be at least as accurate as other, often more complicated, methods of approximation. Most significantly, both the slot and the quarter-plane approximations are easy to apply and need no prior knowledge of the head field of the particular geometry under consideration.

Analytic solutions for double-element shielded magnetoresistive heads

New analytic solutions are presented for idealized mathematical models of double-element shielded magnetoresistive (MR) magnetic recording heads. Two types of heads are considered, represented by poles of either equal or opposite magnetic potentials, each in the presence of an infinitely permeable underlayer. The solutions for heads without underlayers are special cases of the more general results. Typical field plots and spectral response functions are given and comparisons are made with published approximate solutions.

Vector recording in perpendicular media

A dynamic hierarchical micromagnetic model has been used to study the effect of off-axis (in-plane) fields upon the recording properties of perpendicular media. The transient and high-frequency switching response are improved. On longer timescales, the susceptibility and squareness are significantly increased. However, transitions written in the medium with a pole head change only slightly when the in-plane field is included. This is because the transition gets written at a point where the head field gradient is lower and because in-plane demagnetizing fields act to reduce the in-plane head field.

Exact field calculations for conventional and graded magnetization thin film recording heads

A new and exact solution for the magnetic field of a thin film recording head in the presence of a high permeability magnetic underlayer is presented. Typical Fourier coefficients and corresponding fields are given. The leading term alone of the Fourier solution is shown to be more accurate than other previously published approximations when used in conjunction with an integral representation. A novel proposal of variable pole potential is analyzed in a similar manner and significant improvements in peak field strength, field gradients and the absence of secondary field peaks are demonstrated and quantified. >

Analytic three-dimensional response function of a double-shielded magnetoresistive or giant magnetoresistive perpendicular head

Using the Fourier method, we have derived a three-dimensional, fully analytic model of a shielded magnetoresistive or giant magnetoresistive head for perpendicular replay. The head may include side shields. The field and the spectral response function are expressed in closed form. Here, we use the model to show the effect of varying the sensor-shield spacings and the air-bearing-surface-underlayer separation on the field and response of the sensor at high areal density.

A theoretical analysis of shielded magnetoresistive heads by conformal mapping

A new theoretical analysis of an asymmetrically shielded magnetoresistive sensor in the presence of a high-permeability underlayer is obtained by conformal mapping. The symmetrically shielded head is a special case. The solution also covers recessed sensors, and can be extended to the no underlayer situation. Head fields, spectral response functions, phase, dibit shift, and roll-off results for various head configurations are provided and discussed.

A graded magnetization single pole head for perpendicular recording

The magnetic field of a graded magnetization single pole head in the presence of a highly permeable magnetic underlayer is analyzed. Vertical field amplitudes and gradients in the region close to the trailing edge of the pole are shown to be higher than those produced by a conventional single pole. For a perpendicularly magnetized medium, output spectral response functions, roll-off curves and peak shift computations indicate improved replay performance. The exact theoretical solution is obtained in the form of an infinite series using Fourier analysis but it is shown that the leading term alone can lead to a simple and accurate approximation. New theoretical results are also presented for a constant potential pole, including a simple approximation to the field and explicit exact formulae for certain output calculations. >