ADDING ELEMENTS TO THE CO LAYER IN CO/PT MULTILAYERS

In order to determine which elements added to the Co layer in Co/Pt multilayers will reduce the Curie temperature with no significant decrease in the Kerr rotation angle, the magneto-optical (MO) properties of (Co(1-x)M(x))/Pt (M:additional elements) multilayers were studied, taking into account the change in MO properties brought about by varying Pt layer thickness while maintaining Co layer thickness. The addition of any element simultaneously decreases Curie temperature T-c and Kerr rotation angle almost proportionately to the reduction in saturation magnetization M(s). The perpendicular magnetic anisotropy energy K-u also declines with the addition of another element, but for Ni, Fe, and Tb the change is small. The ratio Q of K-u toetization energy, which represents the effective perpendicular magnetic anisotropy, degrades with X, due to the enlargement of M(s) for Fe-added films, while Ni and Tb preserve a large e. Although the Tbstructure above X=0.2, Ni and Fe hardly change the structure even if added in large amounts. As a result, the addition of Ni can control MO properties, keeping large effective perpendicular magnetic anisotropy without influencing the structure. (Co,Ni)/Pt films possess lower T-c than Co/Pt films with the same M(s), and the disks using (Co,Ni)/Pt films achieved higher write sensitivity and higher write/erase cyclability owing to the lower T-c than Co/Pt disks with the same carrier-to-noise ratio. It would seem, therefore, that (CoNi)/Pt multilayers are more promising for practical MO disks.