Harry Sam Edelman

Side-Track Erasure Processes in Perpendicular Recording

In perpendicular recording, substantial erasure of the stored data patterns could occur during writing process. Among all those erasure processes, the sidetrack erasure (STE) is one of the critical erasure issues. To sort out the intrinsic characteristics of the STE process and deepen our understanding of the underlying physics in the erasure processes, in this work, we have experimentally investigated the general attributes of STE process in various situations and quantified some of its distinctive signatures as well as some of its origins. Particularly, some STE behaviors have been characterized thoroughly by employing both the amplitude and BER based STE measurement methods in combination with other unique characterization techniques, in order to unambiguously reveal some of inherent features of the STE processes.

Thermal Magnetic Noise From Synthetic Antiferromagnets in Magnetoresistive Heads

Thermal magnetic noise in magnetoresistive read heads was studied extensively in recent years. It is believed that thermal magnetic noise is becoming the dominant noise source in read heads for hard-disk drive applications. Most previous work concentrated on magnetic white noise from free layers. This work shows that magnetic noise from a synthetic antiferromagnet can be comparable to that from a free layer in tunneling read heads for current and future hard-disk drives. An analytical model is established for thermal magnetic noise based on the single domain particle assumption. The model agrees well with results from a full micromagnetic model. This indicates that magnetic thermal fluctuations in current tunneling heads are close to being coherent.

Performance of U-Pole Writers With Straighter Field Contours

Curvature of transitions recorded onto a magnetic disc has become more pronounced as tracks narrow. Curvature creates interference between adjacent transitions recorded at high bit density, and broadens the read back signal pulse. Curved transitions have a shape similar to that of the field contours that write them. A concave write pole trailing surface, or “U-pole”, pushes the field contours near the pole edges farther down track. This straightens the contours by partially compensating for transition curvature. We used a track trimming technique to compare transition curvature of flat poles and U-poles, and verified that the U-pole reduced curvature by more than 30%. We also demonstrated that the more curved transitions written by flat poles generate ~ 1 nm more pulse broadening at the track edge relative to those written by U-poles. However, modeling predicts a ~ 10% loss in down track field gradient near the center of a U-pole. Measurements of bit error rate across the track confirm the corresponding loss in U-pole performance relative to a flat pole over all but the outer portions of a track.

SAL-BIASED MR HEADS STABILIZED BY CANTED PERMANENT MAGNETS

Abstract The design and fabrication of anisotropic magnetoresistance (AMR) heads biased with a soft-adjacent layer (SAL), stabilized by canted permanent magnet (PM), have been investigated. MR linear response to AC writer current was observed. The response of bias point to DC writer current in overlaid head stronger than abutted head indicates that this MR response to writer is at two side-wings in overlaid head while at the track edges in abutted head. This MR response to writer current can be minimized for narrow track recording by adjusting magnetization angle and strength of PM, which is confirmed by full track scan and micro-track profiles.