Patent ID: 7901802

Claim:
A magnetic recording medium for perpendicular magnetic recording, said recording medium comprising: a substrate; a soft underlayer structure disposed over said substrate, an intermediate layer disposed over said underlayer structure; and a perpendicular magnetic recording layer disposed over said intermediate layer, and wherein said soft underlayer structure comprises five soft magnetic layers μ 1 to μ 5 , with soft magnetic layer μ 5 nearest the substrate having the highest magnetic permeability, soft magnetic layer μ 1 nearest the recording layer having the lowest magnetic permeability, and soft magnetic layers μ 4 , μ 3 and μ 2 having magnetic permeabilities less than the magnetic permeability of the soft magnetic layer μ 5 and greater than the magnetic permeability of the soft magnetic layer μ 1 , wherein the soft magnetic layers are each separated by a non-magnetic spacer layer comprising a material selected from Ru and Ta, wherein a permeability (μ) of the soft magnetic layers is selected to form a gradient that increases across the depth of the soft underlayer structure from a soft underlayer nearest the recording layer to a soft underlayer nearest the substrate, and wherein: soft magnetic layer μ 5 is a material selected from FeTa a Nb b , wherein a is from 5 to 10 and b is from 5 to 10; and FeZr a , wherein a is from 5 to 15; soft magnetic layers μ 4 and μ 3 are materials selected from CoZr a Ta b , wherein a is from 2 to 8 and b is from 5 to 12; CoZr a Nb b , wherein a is from 2 to 8 and b is from 5 to 12; CoFe a B b , wherein a is from 10 to 20 and b is from 5 to 20; CoFe a Si b , wherein a is from 10 to 20 and b is from 5 to 20; or CoFe a Si b B c , wherein a is from 10 to 20, b is from 5 to 10 and c is from 5 to 20; and soft magnetic layers μ 2 and μ 1 are materials selected from Co a B b , wherein a is from 40 to 70 and b is from 30 to 60.