Magneto-optic media

Optical media are now available in three main formats; disk, tape and card. Of these, the disk format is dominant, and available in diameters ranging from a maximum of fourteen inches, down to the new Sony Minidisc at only 2.5 inch diameter. Three families of media also exist, these being ROM (read only memory), WORM (write once read many) and rewritable. Hybrid media, containing more than one of these families on a single substrate, are also coming into existence. Magneto-optic rewritable media currently employ active layers comprising alloys of rare earth metals such as terbium and gadolinium, with transition metals such as iron and cobalt. These alloys exhibit the magneto-optic Kerr effect, whereby the surface optical property of the recording film depends on its magnetic condition. Hence, information can be written by generating magnetic domains in an amorphous film