Thickness dependence of magnetic properties in GdDy/FeCo film

For a better understanding of the dynamic characteristics of GdDy/FeCo magnetooptical (MO) disks, the magnetic properties of GdDy/FeCo films with various thicknesses were investigated. The MO layer, whose thickness was varied from 200 Å to 1500 Å, was sandwiched by dielectric SiN layers. Kerr rotation angle decreased as the MO layer was made thinner, while the reflectivity showed little change. T_comp shifted lower with decreasing thickness, while T_c was constant. The CNR value saturated above 600 Å thickness, while noise level was less influenced with the thickness. Therefore, the increase in CNR is mainly due to the carrier level and caused by an increase of Kerr rotation angle. The degradation of CNR at lower magnetic fields is also discussed