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 thick ness was varied from 200 Angstrom to 1500 Angstrom was sandwiched by d ielectric SiN layers. Kerr rotation angle decreased as the MO layer wa s made thinner, while the reflectivity showed little change. Tcomp shi fted lower with decreasing thickness, while Tc was constant. This is a ssumed to be caused by the effective composition shift of rare-earth i n thinner layers. The CNR value saturated above 600 Angstrom 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 ma gnetic fields tends to be smaller as the thickness is made thinner, ow ing to the lower noise level caused by decreasing demagnetization of t he fields.