Magnetooptical memory experiments on a rotating Mn-Cu-Bi disk medium

A thin film of a new magnetooptical memory medium, Mn-Cu-Bi, was prepared on a glass disk and their dynamic memory characteristics were examined with an experimental rotating disk exerciser. The Curie temperature of the medium was about 200°C. Curie-point writing was made on it. The written information was read by the Kerr effect. The Kerr rotation was ±1.3° at an Ar ion laser wavelength of 5145 Å, where the Kerr rotation of the medium was made maximum by an SiO overcoating. For track selection, a moving coil with a linear motion air bearing, whose shaft was rectangular in form, was used. By utilizing a laser for the light source of a moiré fringe measurement technique, an accurate track access was made possible. The accuracy was within 1 μm and the track-to-track transfer time was about 5 ms. Writing and reading were accomplished under computer control with the direct memory access mode. A 5.09 × 10^-6medium error rate without error correction was obtained for a 2.5 × 10⁵bit/cm²packing density at a data transfer rate of 0.5 MHz.