Patent ID: 8277962

Claim:
A magnetic stack comprising: a substrate; a soft underlayer structure disposed over said substrate, said underlayer structure comprising: a first anti-parallel coupled soft magnetic layered unit proximal the substrate and having a first magnetic permeability, wherein the first anti-parallel coupled soft magnetic layered unit comprises two layers of a soft magnetic material anti-parallel coupled through a non-magnetic Ru layer disposed between the layers of soft magnetic material, a second anti-parallel coupled soft magnetic layered unit that is disposed over said first anti-parallel coupled soft magnetic layered unit and having a second magnetic permeability, wherein the second anti-parallel coupled soft magnetic layered unit comprises two layers of a soft magnetic material antiparallel coupled through a non-magnetic Ru layer disposed between the layers of soft magnetic material, a thickness of the first anti-parallel coupled soft magnetic layered unit is greater than a thickness of the second anti-parallel coupled soft magnetic layered unit, and the thickness of the first soft magnetic layered unit relative to the thickness of the second soft magnetic layered unit is configured to provide an adjacent track erasure (ATE) of less than about 0.5% and an overwrite (OW) greater than about 35 dB in response to exposure of the magnetic stack to a magnetic field sufficient to write data to the magnetic stack, and a non-magnetic exchange break spacer layer between and in direct contact with the first and second anti-parallel coupled soft magnetic layered units, and wherein said first magnetic permeability is higher than said second magnetic permeability; an intermediate layer disposed over said underlayer structure; and a magnetic recording layer disposed over said intermediate layer.