Patent ID: 7625644

Claim:
A perpendicular magnetic recording medium comprising at least a non-magnetic grain size control layer, a magnetic recording layer containing a ferromagnetic material, and an overcoat laminated by turns on a non-magnetic substrate, wherein the magnetic recording layer contains Co, Pt, Cr, Si, and O; the ratio of the number of O atom to the number of Si atom in the magnetic recording layer is between about 2.5 and 5; the Si atomic composition therein is between about 3 atomic % and 6 atomic %; the O atomic composition therein is between about 12 atomic % and 20 atomic %; and coercivity in the direction normal to the media plane is distributed within about +10% of an average value of an in-plane distribution of perpendicular coercivity in the medium, and wherein the non-magnetic grain size control layer comprises a Ta layer and a Ru layer deposited in turn.