A wide area track erasure (WATER) rate of change is determined from a model generated from a plurality of track erasure measurements performed on a magnetic recording media. A model of the change in noise amplitude for an off-track position as a function of the number of aggressor track writes employed in the track erasure measurements is generated. In a log-linear space a linear fit of the change in noise amplitude with respect to the number of aggressor track writes yields a rate of noise amplitude change (dB/decade) which may be utilized to rank magnetic recording media.

Predictive characterization of adjacent track erasure in recording media

A boundary-element method is introduced for solving electromagnetic scattering problems in the frequency domain relative to an impedance boundary condition (IBC) on an obstacle of arbitrary shape. The formulation is based on the field approach; namely, it is obtained by enforcing the total electromagnetic field, expressed by means of the incident field and the equivalent electric and magnetic currents and charges on the scatterer surface, to satisfy the boundary condition. As a result, this formulation is well-posed at any frequency for an absorbing scatterer. Both of the equivalent currents are discretized by a boundary-element method over a triangular mesh of the surface scatterer. The magnetic currents are then eliminated at the element level during the assembly process. The final linear system to be solved keeps all of the desirable properties provided by the application of this method to the usual perfectly conducting scatterer; that is, its unknowns are the fluxes of the electric currents across the edges of the mesh and its coefficient matrix is symmetric.

A boundary-element solution of the Leontovitch problem

Methods for measuring media performance associated with adjacent track interference are provided. One such method includes iteratively writing data to a target track for each of a plurality of n frequencies, measuring a first signal amplitude and a first noise for each of the n sectors on the target track, writing an aggressor track pattern proximate the target track, measuring a second signal amplitude and a second noise for each of the n sectors on the target track, calculating a weighted sum for each of the signal amplitude measurements for each of the plurality of n frequencies, and calculating a weighted sum for each of the noise measurements for each of the plurality of n frequencies, and repeating the writing the aggressor track pattern, the measuring the second signal amplitude and the second noise, and calculating the weighted sums for preselected numbers of times.

Methods for measuring media performance associated with adjacent track interference

The dependence of write, read, and erase widths on current and frequency for thin-film inductive (TFI) and inductive-write/magnetoresistive-read (MR) heads was studied. Currents of up to 150 mA and frequencies of up to 40 kFCI were used to write tracks. The widths were measured from ferrofluid patterns and electrical track scans. For both heads, the write width decreases but the side-erase width increase with increasing frequency. The relationship of these results to head-field contours, established from scanning magnetooptic imaging measurements, is discussed. >

Effects of current and frequency on write, read, and erase widths for thin-film inductive and magnetoresistive heads

The feasibility of high track density recording in a perpendicular magnetic recording system has been investigated. The properties of the magnetic field of a single pole type (SPT) head having a narrow track width were studied by using a large scale model of a head and a medium. The y-field gradient of the SPT head near the track edge is steeper than the x-field gradient of a ring head, and it was confirmed by Bitter technique that the recorded track width acculately coincides with the width of the main pole of the SPT head. Perpendicular recording using the SPT head also has superior off-track characteristics and the crosstalk signal is hardly detected even at very narrow track pitches. From a magnetics point of view, no problems exist in narrowing the track width of the SPT head in perpendicular recording. Narrow track recording and reproducing with SPT head of only 6.5 μm in track width could be achieved with sufficient signal to noise ratio in perpendicular flexible disk systems.

Perpendicular recording by a narrow track single pole head

In magnetic recording systems the side fringing fields of magnetic recording heads are responsible for crosstalk from adjacent tracks and eventually for partial erasure of adjacent tracks, thereby limiting the attainable track density In this paper we derive analytical expressions for the magnetic field near the side of a recording head and calculate the cosine transform of the longitudinal field component, with the head side angle and gap length as parameters The field of a head of zero width is also considered Due to the side fringing field the written track is somewhat wider than the geometrical head width; the increase in width being approximately proportional to the maximum field strength in the recording medium and the head-to-medium distance The amplitude u of the read crosstalk signal from an adjacent, infinitesimally narrow track is calculated and it appears that it can be approximated by u/u_{0} = 05 \exp (-2\pi x/\lambda) , where u 0 is the on-track signal (with zero head-to-medium spacing), x is the distance between track and head side, and λ is the wavelength Maximum track densities are calculated for a specified crosstalk-to-signal ratio and a given head width and wavelength For a wavelength of 10 μm, a head width of 5 μm, and a crosstalk of -20 dB, the track density is limited to about 130 tracks/mm, assuming a track width equal to the head width When the track is taken to be 5 μm wider than the head to account for the effects of the write process, no guardband at all is needed for -20 dB crosstalk and the limit to the track density is 100 tracks/mn

Side fringing fields and write and read crosstalk of narrow magnetic recording heads

Narrow track recording heads suffer from wavelength dependent side fringing effects. During writing these manifest themselves in track widening and erasing of neighboring tracks, and during reading in side fringing response and crosstalk. Side fringing fields have been analyzed theoretically but experimental verification of this phenomena is scarce. Measured values of actual track width, erasing width and crosstalk are reported. The measurements have been performed with specially manufactured disk heads with widths ranging from 10-50 μm. One set of heads was constructed similar to the 3330-II heads. Another set was constructed such that they resemble as closely as possible the shape of the theoretical head that is used as a model. Some heads were locally narrowed by laser machining. Actual track width was measured as a function of write current amplitude at low recording density (no pulse crowding) and as a function of wavelength at optimum write current amplitude. The measured track widening agrees with theory and can be as high as 5 μm at either side of the head at optimum write current and low pulse density. Track widening decreases with decreasing wavelength. The distance from the head side at which the head still effectively erases can be as high as 15μm. In a disk drive this will be the factor that limits the track density. Inter track read crosstalk is determined by measuring the displacement curve (i.e., the curve representing the read signal versus position as the head is shifted across its own track at different wavelengths). The curves agree with theory except for the presence of "side lobes."

Measurement of side-write, -erase and -read behaviour of conventional narrow track disk heads

The side write and crosstalk behavior of longitudinal and perpendicular recording using different head types is analyzed theoretically. Results for the semi-infinite wedge head model, a finite head with a gap, a single pole (SP) head, and a single pole head with a soft magnetic layer below the recording medium are compared. The computations for these head models, except the semi-infinite wedge head model, are carried out by using the "magnetic field surface integral equation method." It appears that the perpendicular recording mode has superior crosstalk properties at high densities for the mentioned head models. The results are compared with those of a vertical dipole head model. A head model which consists of two uniformly charged planes is proposed for the single pole head. The results for this model are in reasonable agreement with the results for the single pole head. Furthermore the model allows fast analytical field calculations.

A discussion on the crosstalk in longitudinal and perpendicular recording

An analytical expression is derived that describes the response of a magnetic read head of finite width to a magnetized track of finite width shifted in the lateral direction. With this expression the side fringing response and crosstalk from adjacent tracks are calculated and a number of results is presented.

Analytical expressions for side fringing response and crosstalk with finite head and track widths

A new numerical technique for computing the three-dimensional magnetic field of a recording head is presented: the "magnetic-field surface-integral equation method". It is based on a vector Green-type integral relation for the magnetic-field strength. The present implementation applies to a recording head configuration consisting of infinitely permeable magnetic materials, perfectly conducting electric shields and a coil, all of arbitrary size and shape. The method is applied to a cubical head with and without magnetic or electric side shields. It is concluded that near the head's sides the harmonic response shows higher long wavelength amplitude oscillations than near the center of the head. The presence of a magnetic side shield is found to decrease considerably the side field, whereas an electric shield, even when perfectly conducting, is much less effective.

A. van Herk

Papers

Side fringing fields and write and read crosstalk of narrow magnetic recording heads

Measurement of side-write, -erase and -read behaviour of conventional narrow track disk heads

A discussion on the crosstalk in longitudinal and perpendicular recording

Analytical expressions for side fringing response and crosstalk with finite head and track widths

Three-dimensional computation of the field of magnetic recording heads