Direct overwrite in magnetooptical recording.

Abstract

Direct overwrite in magneto-optical recording is necessary to overcome the latency incurred by conventional erase before write recording on magneto-optical disks. In this work we theoretically analyze the thermomagnetic recording process on optical disks using a domain wall motion model. The wall motion model developed in this work can be used to examine overwrite schemes on both bilayer and single layer disks, that either rotate beneath an optical head or remain stationary. The model is directly compared with experiment for a GdTbFe direct overwrite sample, and is shown to produce results that are in agreement with experimental observations. We show that variations in the domain wall saturation velocity can mean the difference between writing or erasing a bit on the disk, and hence is a critical parameter in the recording process. We also show that direct overwrite by means of interior nucleation is highly unlikely. Rather, we show that the recording process involves a dynamic balance between those pressures which act to move the domain wall and those which act to freeze it into place. Finally we analyze the Nikon bilayer direct overwrite scheme, and then demonstrate an alternative bilayer overwrite scheme which avoids a major problem with the Nikon scheme.