High speed recording on MnBi thin films deposited on discs

In the case of a rotating disc memory system with optical access, the effects of the rotating speed and of the depth of focus are investigated. It is shown that for high speeds and short pulse durations, the written bits are shifted with respect to their static position. A "writing depth" can be defined from the variations of the bit diameters versus the depth of focus. The threshold properties of the thermomagnetic writing allow this writing depth to increase by increasing the light spot diameter at constant bit size. The effect on reading of increasing the spot diameters is then studied and data on the high frequency modulation of the reading beam are shown. This kind of detection allows the attainment of data rates compatible with the existing memories, but with higher densities.