Patent ID: 8501330

Claim:
A stack, comprising: a 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, wherein the first sub-layer comprises a first magnetic material and a thickness δ 1 ; the second sub-layer comprises a second magnetic material and a thickness δ 2 ; 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, wherein the recording layer is configured so that application of an external magnetic field to the recording layer induces a progressive reversal process of an initial magnetization direction of each of the plurality of columnar-shaped magnetic grains which results in reversal of the initial magnetization direction to yield a final magnetization direction.