ANISOTROPY OF AMORPHOUS Gd-TM FILMS AND ITS APPLICATION FOR DOW AND MSR RECORDING

The recording properties of common single layer magneto-optical (MO) disks can be improved by introducing exchange coupled rare-earth (RE) transition-metal (TM) films, both from the point of view of capacity and data transfer rate. MO multilayer stacks must exhibit exchange coupling in order to be suitable for direct overwrite (DOW) and magnetic superresolution (MSR). Thin DOW stacks require an interface layer to adjust the exchange coupling. Soft magnetic Gd-Fe and Gd-FeCo interface layers exhibit suitable magnetic properties to meet the DOW demands. The best solution would be a RE-TM interface layer with inplane anisotropy at room temperature and perpendicular anisotropy at elevated temperatures. Such a layer can also be used as a read-out layer in MSR stacks. Therefore we studied the anisotropy of evaporated and sputtered Gd-TM films as a function of composition. Gd-FeCo films with a Co/(Fe+Co) ratio less than 0.47 showed a transition from inplane to perpendicular anisotropy with increasing temperature. The transition temperature Ttrans depends on the Co/(Fe+Co) ratio and the Gd content and can be adjusted between 0 K and TC. The temperature range ΔTtrans, where the magnetization direction changes from totally inplane to totally perpendicular, was 70 ± 25 K for all evaporated samples while it depends on Ar pressure for sputtered samples. Triple layer DOW disks showed a maximum CNR of 51.4dB.