“…The PMR media used in commercial HDDs employ the double magnetic layer structure consisting of a semi-hard magnetic recording layer stacked on a soft magnetic underlayer, which is the basic PMR structure proposed by Prof. Iwasaki 1) . Until late 1990's, the Co-alloy recording layer was deposited directly on a thick softmagnetic underlayer of crystalline Fe-Ni 94,95) , amorphous Co-Zr-Nb 11,96) , etc. However, a series of research has shown that the medium noise can be reduced by introducing a thin nonmagnetic layer between the soft magnetic underlayer and the semi-hard recording layer, where the nonmagnetic layer is now defined as an intermediate layer since the soft magnetic layer is called as "underlayer" in the double layer structure 97) .…”