Direct Overwrite for Fixed Bit-Cell Encoding

Abstract

We have recently introduced a new direct overwrite (DOW) scheme for magneto optic (MO) recording based on the double compensation point media using light intensity modulation [1]. The major advantages of this scheme are the elimination of the initialization magnet, simpler disk structures and a wide range for Curie temperatures, thicknesses, and coercivities of the individual layers. One configuration consists of two magnetic layers (memory and reference having perpendicular anisotropy) exchanged coupled through an intermediate soft magnetic layer. The second media configuration consits of only a memory layer and an intermediate layer. The memory layer has a Curie temperature that is greater than, or approximately equal to that of the reference layer. The intermediate layer has a higher Curie temperature than either the memory layer or the reference layer. The room temperature coercivity of the memory layer is higher than that of the reference layer. The combined magnetization of the coupled layers exhibits two compensation points: antiferromagnetic coupling occurs between the memory and reference layers over at least part of the temperature range. The thickness and composition of the two layers are chosen so that the combined system has a compensation temperature above the ambient temperature but below the write temperature. When such a medium is irradiated with low power (Plow) and high power (Phigh) laser beams under constant bias field, the magnetization of the memory and reference layers change as shown in Fig. 1.