Perpendicular magnetic recording medium and magnetic storage apparatus

1. A perpendicular magnetic recording medium comprising:

a nonmagnetic seed layer;

a nonmagnetic intermediate layer provided on the nonmagnetic seed layer; and

a perpendicular recording layer provided on the nonmagnetic intermediate layer,

wherein the nonmagnetic seed layer includes a first seed layer made of a NiW alloy having a fcc structure, and a second seed layer provided between the first seed layer and the nonmagnetic intermediate layer and made of a NiWNb alloy having a fcc structure, and

a content of one or more elements other than Ni within the NiWNb alloy forming the second seed layer and having a Goldschmidt radius greater than that of Ni is larger than a content of one or more elements other than Ni within the NiW alloy forming the first seed layer and having a Goldschmidt radius greater than that of Ni.

2. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the first seed layer includes Ni as a main component and W and at least one element selected from a group consisting of W, Nb, Ta, Mo and Zr.

3. The perpendicular magnetic recording medium as claimed in claim 1 , wherein a composition ratio of all elements other than Ni within the NiW alloy forming the first seed layer is 1 at. % to 12 at. %.

4. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the first seed layer has a thickness of 1 nm to 5 nm.

5. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the first seed layer has a thickness of 2 nm to 4 nm.

6. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the second seed layer includes Ni as a main component and W and Nb and at least one element selected from a group consisting of Ta, Mo, Zr and Al.

7. The perpendicular magnetic recording medium as claimed in claim 1 , wherein a composition ratio of all elements other than Ni within the NiWNb alloy forming the second seed layer is 2 at. % to 16 at. %.

8. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the second seed layer has a thickness of 1 nm to 5 nm.

9. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the second seed layer has a thickness of 2 nm to 4 nm.

10. The perpendicular magnetic recording medium as claimed in claim 8 , wherein a total thickness of the first and second seed layers is 3 nm or greater.

11. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the nonmagnetic intermediate layer is made of Ru or an alloy having Ru as a main component.

12. The perpendicular magnetic recording medium as claimed in claim 1 , further comprising:

a substrate; and

a soft magnetic underlayer provided on the substrate,

wherein the soft magnetic underlayer is made of a crystalline or amorphous material including Co and Fe.

13. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the perpendicular recording layer includes one or more magnetic layers made of a granular magnetic material.

14. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the perpendicular recording layer includes a first magnetic layer made of a granular magnetic material and provided on the nonmagnetic intermediate layer, and a second magnetic layer provided on the first magnetic layer and having a magnetic anisotropy smaller than that of the first magnetic layer.

15. A magnetic storage apparatus comprising:

at least one magnetic recording medium; and

a transducer configured to write information on the magnetic recording medium and/or read information from the magnetic recording medium,

wherein the magnetic recording medium employs a perpendicular magnetic recording technique and includes a nonmagnetic seed layer, a nonmagnetic intermediate layer provided on the nonmagnetic seed layer, and a perpendicular recording layer provided on the nonmagnetic intermediate layer,

wherein the nonmagnetic seed layer includes a first seed layer made of a NiW alloy having a fcc structure, and a second seed layer provided between the first seed layer and the nonmagnetic intermediate layer and made of a NiWNb alloy having a fcc structure, and

a content of one or more elements other than Ni within the NiWNb alloy forming the second seed layer and having a Goldschmidt radius greater than that of Ni is larger than a content of one or more elements other than Ni within the NiW alloy forming the first seed layer and having a Goldschmidt radius greater than that of Ni.

16. The magnetic storage apparatus as claimed in claim 15 , wherein the first seed layer of the magnetic recording medium includes Ni as a main component and W and at least one element selected from a group consisting of W, Nb, Ta, Mo and Zr.

17. The magnetic storage apparatus as claimed in claim 16 , wherein the first seed layer of the magnetic recording medium has a thickness of 1 nm to 5 nm.

18. The magnetic storage apparatus as claimed in claim 15 , wherein the second seed layer includes Ni as a main component and W and Nb and at least one element selected from a group consisting of Ta, Mo, Zr and Al.

19. The magnetic storage apparatus as claimed in claim 18 , wherein the second seed layer of the magnetic recording medium has a thickness of 1 nm to 5 nm.

20. A perpendicular magnetic recording medium comprising:

a nonmagnetic seed layer;

a nonmagnetic intermediate layer provided on the nonmagnetic seed layer; and

a perpendicular recording layer provided on the nonmagnetic intermediate layer,

wherein the nonmagnetic seed layer includes a first seed layer made of a NiW alloy having a fcc structure, and a second seed layer provided between the first seed layer and the nonmagnetic intermediate layer and made of a NiW alloy having a fcc structure, and

a content of one or more elements other than Ni within the NiW alloy forming the second seed layer and having a Goldschmidt radius greater than that of Ni is larger than a content of one or more elements other than Ni within the NiW alloy forming the first seed layer and having a Goldschmidt radius greater than that of Ni,

wherein the first seed layer includes Ni as a main component and W and at least one element selected from a group consisting of Nb, Ta, Mo and Zr; and the second seed layer includes Ni as a main component and W and at least one element selected from a group consisting of Nb, Ta, Mo and Zr.