Chapter 4 - Write process in magnetic recording

Abstract

This chapter describes an analytical model on digital magnetic write process, the William-Comstock model. In order to reproduce well-defined voltage pulses from a magnetic medium, sharp magnetic transitions need to be written. The concept of nonlinear distortions in the write process, including partial erasure, nonlinear transition shift, and hard transition shift are introduced. Digital magnetic write process is based on so-called saturation recording. The magnetization of the medium is more or less saturated by the write field―any increase of input current will not result in a proportional increase in magnetization. This is, of course, one of the basic characteristics of a nonlinear process, and thus the write process in digital magnetic recording is generally nonlinear as opposed to the readback process. Furthermore, interactions between magnetic grains and the existence of a demagnetizing field lead to nonlinear distortions. These phenomena must be well understood and controlled to achieve high-density magnetic recording.