A direct-overwrite system for magneto-optical systems with a soft-magnetic shield

A direct overwrite system for magnetooptical storage systems is analysed which includes an extra field source in the form of a thin permanent magnetic film and a soft magnetic shield between the memory and field-source layers. Locally, the shielding power of the soft film can be canceled purposefully by raising the temperature above its Curie temperature by selecting an adequate power level of the write laser. Thus, the field of the extra field source can penetrate through the paramagnetic hole into the writeable region of the storage layer, and controls the magnetization direction in the latter. The groove structure in the disk surface is used to obtain fringing fields induced by the second field source outside this layer. A suitable structure of the film stack is analyzed by finite element calculations, which show that write fields can be obtained up to 2.5 kA/m. The development of the paramagnetic hole in the soft layer and its position with respect to the writeable region is studied as a function of the shape of the laser power, the physical parameters of the layers, and the disk velocity. It is concluded that a pulse frequency of about 10 MHz should be possible