Patent ID: 7572526

Claim:
A perpendicular magnetic recording medium comprising: a substrate; and an exchange-spring structure on the substrate and comprising: a first ferromagnetic layer on the substrate and having an out-of-plane easy axis of magnetization; a second ferromagnetic layer having an out-of-plane easy axis of magnetization, the second ferromagnetic layer having an anisotropy field less than about 70% of the anisotropy field of the first ferromagnetic layer; a first coupling layer on the first ferromagnetic layer and between the first and second ferromagnetic layers and permitting ferromagnetic coupling of the first ferromagnetic layer with the second ferromagnetic layer; a third ferromagnetic layer having an out-of-plane easy axis of magnetization, the third ferromagnetic layer having an anisotropy field greater than the anisotropy field of the second ferromagnetic layer and less than about 70% of the anisotropy field of the first ferromagnetic layer; and a second coupling layer on the second ferromagnetic layer and between the second and third ferromagnetic layers and permitting ferromagnetic coupling of the second ferromagnetic layer with the third ferromagnetic layer.