Introduction

In thermomagnetic recording a focused laser beam creates a hot spot and allows an external magnetic field to reverse the direction of local magnetization. Erasure is similar to recording, except for a reversing of the external field, which enables the magnetization within the heated region to return to its original state. The technology of high-density magneto-optical data storage owes a large measure of its success to the accuracy, reliability, and repeatability of the thermomagnetic process. The recorded domains are highly regular and uniform, fully reversed, and free from instabilities. What is more, a given area of the storage medium can be erased and rewritten several million times without any degradation.

The present chapter is devoted to the analysis of the thermomagnetic process based on the physical principles of micromagnetics and domain dynamics. In section 17.1 we review some of the facts and experimental observations concerning the storage media and the recording process. This will help familiarize the reader with the variety of phenomena and the order of magnitude of the parameters involved, and will set the stage for in-depth analyses of thermomagnetic recording in subsequent sections. The discussion in section 17.2 revolves around the energetics of domain formation and the forces acting on the domain wall in its formative stages. This treatment of the problem, being based on the arguments described in section 13.3, is essentially a quasi-static treatment that ignores the dynamics of wall motion; moreover, it fails to properly account for the role of coercivity in the recording process.