Terence T. Lam

Narrow track recording characteristics in thin film media

In this paper, we report a combined spin-stand measurement and micromagnetic simulation study on narrow track recording characteristics in thin film media. It is found that the onset recording density of nonlinear partial erasure is determined by intertransition percolations near the track edges where the head field gradient is poor. Trimming into the shared pole in merged MR/thin film heads is necessary for performance at both high linear and high track densities. Increasing head field magnitude with respect to medium coercivity increases the width of erase band but not the actual transition track width. When the head is skewed, the edge field overwrites on-track transitions, resulting in a reduction of effective transition track width. The trimming of the shared pole in merged MR/thin film heads can significantly reduce this edge overwrite effect. It is suggested that servo writing schemes should be modified to take into account the phenomena described in this paper.

Experimental study of track edge noise distribution in narrow track recording

Time domain measurements were conducted on a precision spin stand tester to obtain two dimensional mappings of track edge noise in longitudinal thin film media. Read back voltage waveforms were repeatedly captured by a real time digitizer, and media noise power was obtained by calculating the ensemble variance of the waveform. The same procedure was repeated for different track positions ranging from on-track to totally off-track, and a two dimensional mapping was obtained. A conventional untrimmed thin-film inductive head was used to record the data patterns. On readback, a magneto-resistive read head was used because of its relatively narrow cross-track sensitivity function. Away from transitions, edge noise is uncorrelated and is distributed only along the sides of the hard-bit cells whose magnetization is reversed with respect to the original DC-erase direction. Edge noise enhancement is found when two hard-bit cells are placed in close proximity. >

Affect Of Orientation Ratio On The Recording Characteristics Of Longitudinal Thin Film Media

The effect of orientation ratio on recording characteristics has been experimentally investigated. Thin film longitudinal media with orientation ratios (ORs) of 2.34 and 0.86, having almost the same coercivity, were used in this study. High OR film medium makes the transition sharp, and high signal output and low medium noise are obtained in low densities. However, at high densities, noise power becomes significantly higher than low OR film medium, and strong demagnetization field from previously recorded transition induces nonlinear bit shift of newly recorded transition which results in poor overwrite performance. >

Recording performance of submicron track width thin film heads

This spin‐stand measurement study focuses on recording characteristics at submicron scale track width. The pole tips of a set of identical thin film heads were trimmed from the air‐bearing surface by focused ion beam etching. A set of thin film heads with track widths ranging from W=2 μm to W=0.5 μm were produced. Recording experiments were performed on a high precision spin‐stand tester using these heads. Both on‐track and off‐track performances were studied and analyzed. As the track width is scaled down, degrading of recording performance is observed. When the width of a recording head is decreased, the onset of partial erasure occurs at a lower density, and the noise power per unit head track width increases. Further investigation on the track profiles reveals that the extent of partial erasure is higher at the track edge as density increases, and this phenomenon is more pronounced in narrower track width heads.

Density and phase dependence of edge erase band in MR/thin film head recording

The erase band resulting from edge overwrite has been studied using magnetic force microscopy. Utilizing image processing techniques, we developed a method to accurately measure the width of the edge erase band. In this paper, we focus on the study of MR/thin film head recording. Our experimental results show the erase band width is strongly dependent on the relative phase of the transitions in the old and new tracks at low bit densities. As the recording density is increased, the erase band width increases and becomes independent of the phase change. The erase band width observed ranges from 0 to 0.7 /spl mu/m for a typical MR/thin film head with 4 /spl mu/m wide trailing pole.

Magnetic force microscopy study of submicron track width recording in thin‐film media

The magnetic force microscopy (MFM) technique is used to investigate the writing properties of a set of thin‐film heads with track widths ranging from 2 to 0.5 μm. MFM images show that track edge percolation occurs at lower densities than on‐track intertransition percolation. Track edge percolation results in track edge fluctuations and effective track width reduction. As the head track width is reduced to the near‐micron or submicron ranges, the track edges become dominant portions of the track and consequently cause severe degradation of the recording tracks. Track edge percolation is caused by a poor edge field gradient and is possibly enhanced by pole tip corner saturation. In order to achieve high‐density narrow track recording, high moment writing heads become necessary.

Effect Of Head Skew On Edge Erasure And Transition Noise At Submicron Recording Track Width

Cross track transition noise profiles and erase band widths were measured on a spin-stand using a 1 /spl mu/m wide focus ion beam trimmed inductive head, at different skew angles. At a 20/spl deg/ skew angle, large asymmetry about the track center in the noise profiles is observed, which is attributed to the self-overwriting of transitions near the edge on the side of the track that has a wider erase band. This self-overwriting at the track edge broadens transitions and leads to track edge percolation at high densities. This causes an effective track width reduction which shows up as an increase in the erase band width in the erase profile measurement.

Phase dependence of track edge noise in MR head written overlapping tracks

Two dimensional distributions of track edge noise in partially overlapping tracks with various phase relationships were obtained using a time domain correlation technique. An additional read/write channel on the spin stand tester was required to generate an accurate trigger signal for controlling the phase of data tracks. The edge noise associated with the overwriting tracks was found to be dependent on their phases with respect to the overwritten tracks. Low edge noise was obtained when the two tracks are in phase, and high edge noise was obtained when they are out of phase.

Cross track distribution of partial erasure

The extent of partial erasure across a written track is measured experimentally on a spin-stand. Using the combined track profiling-1D/3D method of measuring partial erasure, it is found that partial erasure, or intertransition percolation, does not occur uniformly across the track. The portion of transition near the track edges actually percolates at lower densities than the center portion of the track as recording density increases. The overall partial erasure of the track is mainly attributed to the reduction in signal strength near the track edges, results from the reduced head field gradient near the edges of the head poles. This distribution of partial erasure across the track becomes highly asymmetric at large skew angles, especially in narrow track recording systems. Intertransition percolation becomes more severe on the side of the track that has a wider erase band.

Experimental and micromagnetic study of track edge noise reduction effect in multilayer thin film media

A time domain spin-stand tester noise measurement and a micromagnetic modeling study are conducted to investigate the track edge noise reduction effect in multilayer thin film media. Both experimental and modeling studies show that track edge noise is concentrated in the side written band of a reversed bit-cell, in which the magnetization is opposite to the previous dc erased state. The track edge noise level is substantially suppressed for films laminated with a very thin non-magnetic interlayer. Thus the multilayer thin film media is more suitable for future narrow track recording. >