Thermal and magnetic design of 8 MB/s MO disk

A highly power-sensitive and field-sensitive magnetooptic disk has been developed for an 8-MB/s, 3600-rpm, 30-GB, 10-in five-fold stacked disk system. The disk structure is of [Al-alloy/nitride/PtCo/TbFeCo/nitride] on glass-2p substrate. Power sensitivity has been improved by setting the thickness of metal layers thin enough (Al-alloy: 50 nm, TbFeCo: 20 nm) and Curie temperature at 190°C so as to enable the use of a conventional 30-to-40 mW laser. The compensation temperature of TbFeCo is elevated to about 130°C in order to restrict pit size distribution in a narrow range. The thinning of the metal layers also plays a role in precise pit-edge control by restricting written pit expansion to avoid tear-drop-like pit recording. Insertion of a capping layer of PtCo exchange-coupled to TbFeCo on top improves the field sensitivity drastically to obtain a switching field as low as 100 Oe, enabling the reduction of the bias field coil, which is desirable for high-speed devices