Patent ID: 7993764

Claim:
A perpendicular magnetic recording medium comprising: a soft magnetic backing layer, a seed layer, an underlayer, a nonmagnetic intermediate layer, and a magnetic recording layer sequentially disposed on a nonmagnetic substrate, wherein the underlayer consists essentially of cobalt, nickel, iron, and at least one other element selected from a group consisting of Si, B, and Nb, wherein the underlayer has an fcc structure and exhibits soft magnetic property, wherein the underlayer has crystal grains and grain boundaries that isolate the crystal grains from each other to control grain size of the magnetic recording layer and to promote magnetic isolation between crystal grains of the magnetic recording layer, wherein the underlayer contains nickel in a range of 30 at % to 88 at % and iron in a range of 0.1 at % to 22 at %, wherein the underlayer has a thickness of at most 30 nm, wherein the nonmagnetic intermediate layer contains at least one element selected from a group consisting of Ru, Re, Pd, Ir, Pt, and Rh, and wherein the seed layer contains at least one element selected from a group consisting of Ta, Ti, Zr, Cr, Mo, W, Si, Al, Pd, and Pt.