Y. Nishida

Study on the write-field profile and intensity of narrow-track-width SPT head

The effects of the structure of a single-pole-type (SPT) head and the underlayer thickness on the write-field profile and intensity were examined by computer calculation. The results demonstrated the possibility of achieving a strong write field even with a thin underlayer in the case of narrow-track-width SPT. The shorter throat height enhanced the maximum write-field intensity without a great change of the write-field profile. We also proposed a new, tapered SPT head suitable to address the sidewriting issue for drive integration.

Current progress of single-pole-type GMR heads for perpendicular recording

We studied several proposals to address the problems encountered when single-pole-type giant magnetoresistive (SPT-GMR) heads are applied to an actual recording system. The first area of problems was regarding side erasure when there is a head skew. We fabricated a trapezoid-shaped main pole using a focus-ion-beam trimming or using a new wafer-processing technique and examined their write performances and their effects on reducing side erasure. The second area of problems concerned the stray field robustness of SPT-GMR heads when combined with a double-layered perpendicular recording medium. We tried to optimize the robustness and write performance by changing the width of a yoke in the main pole or by positioning a shield above the main pole. The stray field robustness and write performance were adequate in both cases, but a tradeoff relationship exists between both performances.

CoB/Pd multilayers with PtB/Pd/MgO intermediate layers for perpendicular magnetic recording

CoB/Pd multilayer films with a PtB/Pd/MgO intermediate layer were deposited on a soft-magnetic underlayer or on seeded substrates. A TEM analysis revealed that the multilayer films have a well-separated columnar structure just above an MgO layer. This structure may be initiated by the difference in the wetting nature of nonmetallic MgO and metallic Pd, and may be enhanced by the PtB layer. These boundaries were found to act in reducing the exchange coupling, resulting in an improvement in recording performance.

Performance evaluation for FDTS/DF on MR nonlinear channels

We evaluated the performance of fixed-delay tree-search detector with decision feedback (FDTS/DF) when used for nonlinear magneto-resistive (MR) read head channels. The feedback section of the FDTS/DF was replaced by RAM lookup table for nonlinear equalization. The evaluation was based on a computer simulation in which the read-back signal from the MR head was modeled from a measured MR transfer characteristic function and actual real reproduced isolated pulses. Performance was compared to that of PRML channels. We also compared the sensitivity of the FDTS/DF and PRML channels to variations in the recording channel frequency response due to head-medium spacing fluctuation. The results show that the FDTS/DF channel has good resistance to MR nonlinear distortion and channel response variations, and is superior to the PRML channels in terms of realistic recording channel response.

A Study of Thermal Decay Waveform Model in Perpendicular Recording System

The perpendicular recording media are thermally stable in high recording density. We tried to build thermal decay model of waveform and noise for perpendicular recording media based on theoretical and practical approach, in order to estimate BER degradation using channel simulation.

Wide band erasure caused by SUL domain wall in perpendicular recording media

The paper points out that soft magnetic underlayer (SUL) domain wall causes wide-band erasure in perpendicular recording media, and that laminated or multi-layered SUL can avoid this problem. Additionally, the spike noise produced by SUL causes bit error rate (BER) degradation. The types of SUL required to solve neighboring track erasure are similar to the approaches proposed to solve the spike noise problem. Thus, controlling the SUL domain is very important, not only for BER performance, but also for the reliability of the recorded information.

Signal processing and coding techniques for perpendicular recording

Non-stationary media noise is one of the major disturbances that occur in higher density perpendicular magnetic recording channels. The strongly signal-dependent and correlated statistical nature of this noise means that it significantly worsens error-rates of traditional partial-response maximum likelihood (PRML) data-detection. As densities of recording become increasingly high, thermal stability issues place serious restrictions on the use of smaller grained recording media to reduce the media noise. To mitigate requirements for the noise reduction, we have introduced a sub-optimal ML detection scheme for media-noise-dominant channels. This scheme is based on the estimation of signal-dependent correlation-sensitive (SDCS) metric for soft-output postprocessing detection. By focusing on correcting only a few most-likely error-events in PRML detection, this media-noise soft-output detection scheme provides a good tradeoff between detection performance and computational complexity.

CoCrPt-alloy perpendicular media for high-density magnetic recording

CoCr-alloy perpendicular magnetic recording media have been investigated, as the Cr segregated structure in the CoCr-alloy recording layer is suitable for obtaining low noise properties. Recently, the grain size of the recording layer is required to be very small for high-density recording, therefore the thermal stability of the recorded bit is becoming a critical issue. The magnetic anisotropy should be improved to keep the thermal stability of the recording layer which consists of small grains. The addition of the Pt element and a decrease of Cr content are required in the CoCr-alloy. This, however, results in higher medium noise due to increasing inter-granular exchange coupling. In this paper, the effects of Cr content on the magnetic and recording properties in post-annealed CoCrPt-alloy perpendicular media were investigated. The post-annealing treatment is expected to enhance Cr diffusion into the CoCrPt grain boundary from a nonmagnetic CoCr intermediate layer.

Exact analytical expression for medium field from perpendicular medium

In this study, we obtain a simpler analytical expression for the perpendicular medium field without sacrificing accuracy.

CoB/Pd multilayer with PtB/Pd/MgO intermediate layer for perpendicular magnetic recording

In this study, we investigated the effects of PtB/Pd/MgO intermediate layers on the magnetic and recording characteristics of CoB/Pd multilayer media.