Patent ID: 7846564

Claim:
A magnetic recording medium, comprising: (a) a non-magnetic substrate having at least one surface; and (b) a layer stack on said surface of said substrate, said layer stack including a perpendicular recording layer comprising a plurality of columnar-shaped magnetic grains extending perpendicularly to said substrate surface for a length extending from a bottom to a top of said recording layer and having a first end distal said substrate surface and a second end proximal said substrate surface, wherein each of said columnar-shaped magnetic grains comprises a plurality of sub-layers, grain size, and wherein each of said sub-layers of magnetic material in each columnar-shaped magnetic anisotropy field H k that progressively decreases from a sub-layer at said first end to a sub-layer at said second end of each of said magnetic grains and wherein each of the sub-layers comprises a cobalt-based alloy and possesses the H k greater than at least about 1000 Oe.