Erasable magneto-optical recording media

Abstract

Magneto-optical storage techniques in amorphous metal films have the advantages of high bit density and contactless write, read and erasure operations. Digital information is stored as a sequence of small magnetic domains; writing and erasure is performed by local temperature rise (AlGaAs laser heating) in combination with a low external magnetic field. In principle, the number of switching cycles is unlimited. Non destructive readout is achieved via magneto-optical effects. Material and system aspects for erasable compact-disk audio application will be reviewed. Disks are vapour-deposited on pregrooved substrates. Binary and ternary alloys of Gd, Tb combined wlth Fe,Co are highly suitable, storage media. For practical use bi- and multilayer structures were used in order to improve the read-out efficiency and lifetime of the disk. Aging effects were studied by measurements of magneto-optical and magnetic properties and SIMS analysis during the lifetime of the disk. Current results of about 45 dB CNR (30 kHz bandwidth) and a lifetime for the disk of more than 5 years opens the discussion of applications in low- and high-density storage in professional and consumer fields.