Patent ID: 8048545

Claim:
A magnetic recording medium, comprising: a non-magnetic substrate having at least one surface; and a layer stack on the surface of said substrate, the layer stack including a perpendicular recording layer comprising a plurality of columnar-shaped magnetic grains extending perpendicularly between opposing surfaces of the recording layer, wherein each columnar-shaped magnetic grain comprises a plurality of sub-layers including first and second sub-layers with different magnetic compositions, wherein the first sub-layer is positioned at a first end of each of the columnar-shaped magnetic grains and comprises a first magnetic material that includes CoCrX 1 , where X 1 includes at least one element selected from the group Ta, Pt, B V, C, Nd, Cu, Zr, Fe, P, O, Si, and Ni, has a magnetic moment M r from about 200 to about 800 cmu/cc, a relatively high perpendicular anisotropy field H k from about 8,000 to about 20,000 Oe, a thickness δ 1 from about 6 to about 25 nm, and a grain size from about 4 to about 10 nm; the second sub-layer is positioned at a second end of each of the columnar-shaped magnetic grain and comprises a second magnetic material that includes CoX 2 , where X 2 includes at least one element selected from the group C, B, Cr, Pt, O, Fe, Ta, Cu, Nd, Ni, and Ti, with a magnetic moment Mr from about 400 to about 900 cmu/cc, a relatively low perpendicular anisotropy field H k from about 1,000 to about 9,000 Oe, a thickness δ 2 from about 3 to about 15 nm, and a crystal structure and grain size matching those of said first sub-layer; and the total thickness δ 1 +δ 2 of said first and second sub-layers is less than local exchange coupling distances of the first and second magnetic materials.