Magneto-optical (MO) recording combines the advantages of optical recording and magnetic recording. It offers very high storage densities, it is a noncontact technique, and it allows an unlimited number of read/write cycles. Although the potential of magneto-optical recording was recognized nearly 25 years ago, suitable materials did not exist at that time. Since then, substantial efforts have been made optimizing existing materials and searching for new ones. In 1973 an important development was started by Chaudhari et al., who discovered amorphous GdCo with perpendicular magnetic anisotropy as a possible MO recording material. Today amorphous ternary rare-earth (RE) transition-metal (TM) alloys like GdTbFe and TbFeCo are the recording layers in the MO disks which appear on the market. Although these materials show good recording performance, they also exhibit some drawbacks, mainly caused by their susceptibility to oxidarion and corrosion. However, two new classes of suitable MO materials with good oxidation resistance are emerging.
