Exchange-Coupled Double-Layer Magneto-Optical Disk with a Reflecting Layer

Optical enhancement conditions and read/write characteristics for exchange-coupled double-layer magnetooptic (MO) disks were investigated. It was found that the figure of merit (R ^(1/2) ·θ _K ) for an MO disk with a thick (60 nm) magnetic layer is comparable to that of a conventional MO disk with a thin (20 nm) magnetic layer. The write noise level of the thick-magnetic-layer MO disk is markedly lower (2 to 5 dB) than that of the conventional disk. An exchange-coupled double-layer (GdFeCo 30 nm/TbFeCo 30 nm) MO disk, with a large Kerr rotation, moderate reflectivity and low noise level, is suitable for use as a high-performance medium. This MO disk has a C/N ratio of 45 dB at a wave-length of 680 nm, and a mark length of 0.67 pm when polycarbonate substrate with a track pitch of 1.2 μm is used.