Perpendicular magnetic recording medium

1. A perpendicular magnetic recording medium comprising:

a soft magnetic underlayer,

a first seed layer,

a second seed layer,

an intermediate layer,

a granular magnetic recording layer,

a non-granular magnetic recording layer,

a protective layer, and

a lubricant layer

laminated on a nonmagnetic substrate in this order, the first seed layer containing cobalt, nickel, and at least one element selected from a group consisting of Si, Cr, V, Zr, Nb, Ta, Ti, Cu, and Mo, and the second seed layer containing nickel, chromium, and at least one element selected from a group consisting of Si, V, Zr, Nb, Ta, Ti, Cu, and Mo,

wherein a misfit between crystal lattice planes perpendicular to the substrate of the second seed layer and of the intermediate layer is in a range of +5.3% to +6.8%.

2. The perpendicular magnetic recording medium according to claim 1 , wherein the granular magnetic recording layer comprises ferromagnetic crystal grains composed of a cobalt-based alloy and nonmagnetic grain boundaries composed of an oxide(s) of at least one element selected from a group consisting of Cr, Co, Si, Al, Ti, Ta, Hf, and Zr.

3. The perpendicular magnetic recording medium according to claim 1 , wherein the non-granular magnetic recording layer comprises ferromagnetic crystal grains composed of a cobalt-based alloy and nonmagnetic crystal grains composed of at least one element selected from a group consisting of Ta, Pt, B, Si, Nb, Cu, and Ti.

4. The perpendicular magnetic recording medium according claim 1 , wherein a thickness of the first seed layer is in a range of 2 to 8 nm.

5. The perpendicular magnetic recording medium according to claim 1 , wherein a thickness of the second seed layer is in a range of 2 to 12 nm.

6. The perpendicular magnetic recording medium according to claim 1 , wherein a misfit between fcc (220) lattice planes of the first seed layer and of the second seed layer is in a range of −4.5% to +4.5%.

7. The perpendicular magnetic recording medium according to claim 1 , wherein the nonmagnetic substrate is substantially composed of glass, aluminum, or silicon.

8. The perpendicular magnetic recording medium according to claim 2 , wherein the non-granular magnetic recording layer comprises ferromagnetic crystal grains composed of a cobalt-based alloy and nonmagnetic crystal grains composed of at least one element selected from a group consisting of Ta, Pt, B, Si, Nb, Cu, and Ti, a thickness of the first seed layer is in a range of 2 to 8 nm, and a thickness of the second seed layer is in a range of 2 to 12 nm.

9. The perpendicular magnetic recording medium according to claim 8 , wherein a misfit between fcc (220) lattice planes of the first seed layer and of the second seed layer is in a range of −4.5% to +4.5% and a misfit between crystal lattice planes perpendicular to the substrate of the second seed layer and of the intermediate layer is in a range of +5.3% to +6.8%.

10. The perpendicular magnetic recording medium according to claim 9 , wherein the nonmagnetic substrate is substantially composed of glass, aluminum, or silicon.

11. The perpendicular magnetic recording medium according to claim 1 , wherein the first seed layer contains an alloy consisting of cobalt, nickel, and at least one element selected from a group consisting of Si, Cr, V, Zr, Nb, Ta, Ti, Cu, and Mo, and the second seed layer contains an alloy consisting of nickel, chromium, and at least one element selected from a group consisting of Si, V, Zr, Nb, Ta, Ti, Cu, and Mo.

12. The perpendicular magnetic recording medium according to claim 1 , wherein the first seed layer is selected from the group consisting of CoNiCr, CoNiCrSi, CoNiNb, CoNiNbSi, CoNiTa, CoNiMo, CoNiTi, and CoNiVCu.