Patent ID: 6852398

Claim:
Perpendicular magnetic recording media, comprising: a non-magnetic substrate; an underlayer provided on the substrate having predetermined permeability characteristics; a first perpendicular magnetic recording layer provided with perpendicular magnetic anisotropy on the underlayer, which has ferromagnetic grains surrounded with non-magnetic boundaries so that the magnitude of magnetic exchange interaction between the grains is substantially zero; and a second perpendicular magnetic recording layer provided with perpendicular magnetic anisotropy on the first perpendicular magnetic recording layer, which has a polycrystalline structure including ferromagnetic grains wherein boundaries thereof are non-magnetic to make magnetic exchange interaction between grains larger than that in the first perpendicular magnetic recording layer, wherein: an exchange stiffness constant between grains of the first recording layer is 0.05×10 −11 J/m or less; and an exchange stiffness constant between grains of the second recording layer is in a range of 0.15×10 −11 J/m to 0.8×10 −11 J/m; and further wherein: the first recording layer and the second recording layer are alternately laminated as multi-layers and the multi-layers include at least two of said first recording layers and at least two of said second recording layers.