Patent ID: 7736765

Claim:
A granular perpendicular magnetic recording medium, comprising: (a) a non-magnetic substrate; and (b) a granular perpendicular magnetic recording layer overlying said substrate, comprising: (i) a first granular perpendicular magnetic layer proximal said substrate and having a first saturation magnetization (M s ) 1 , wherein the first granular perpendicular magnetic layer consists of a CoPt magnetic alloy and a non-magnetic oxide material at boundaries between adjacent magnetic grains, and wherein the magnetic oxide material in the first granular perpendicular magnetic layer is selected from at least one of TiO 2 , SiO 2 , Nb 2 O 5 , Al 2 O 3 , Ta 2 O 5 , ZrO 2 , V 2 O 5 or Y 2 O 3 ; and (ii) a second granular perpendicular magnetic layer distal said substrate and having a second, different saturation magnetization (M s ) 2 , wherein the second granular perpendicular magnetic layer is directly on the first granular perpendicular magnetic layer, wherein the second perpendicular granular magnetic layer consists of a CoPt magnetic alloy and a non-magnetic oxide material at boundaries between adjacent magnetic grains, and wherein the magnetic oxide material in the second granular perpendicular magnetic layer is selected from at least one of TiO 2 , SiO 2 , Nb 2 O 5 , Al 2 O 3 , Ta 2 O 5 , ZrO 2 , V 2 O 5 or Y 2 O 3 , and wherein: (M s ) 1 is about 200 emu/cc to about 600 emu/cc, and (M s ) 2 is greater than about 600 emu/cc and at least 20% greater than (M s ) 1 .