Effects of bottom layer on recording performance and thermal stability for AFC media

Recording performance and thermal stability of the antiferromagnetically coupled (AFC) media that utilize CoCrPt alloy as the bottom layer were investigated. The dependence of media noise on the bottom layer thickness (t_B) is sensitive to the magnetization of the bottom layer (Ms_B). A strong dependence of media noise on t_B is observed for the media with high Ms_B (>0.7 T). Contrary, the media noise is almost constant in the range of t_B=2--5nm for low Ms_B (<0.7 T). The relationship between Ku·V/kT and t_B is sensitive to anisotropy field of the bottom layer (Hk_B). Thermal stability can be improved by increasing Hk_B, which is noticeable for the media with thicker t_B.