Perpendicular magnetic recording medium having grain boundary layer containing ferromagnetic element
View Patent ↗Embodiments of the invention ensure that a perpendicular magnetic recording medium having a granular magnetic recording layer made of CoCrPt alloy and Si oxide provides both high SNR and thermal stability. In one embodiment, a substantially amorphous grain boundary layer of a magnetic recording layer made of CoCrPt alloy and Si oxide contains a ferromagnetic element in a concentration from about 30 at. % to 50 at. % or more preferably from about 35 at. % to 47 at. %, so that intergrain exchange interaction takes place moderately. As a consequence, SNR of 18 dB or more and thermal stability of 3%/decade or less are achieved.
1. A perpendicular magnetic recording medium including a soft magnetic layer, a non-magnetic intermediate layer, and a magnetic recording layer disposed on a substrate, said magnetic recording layer having a granular structure in which crystal grains are separated by grain boundary layers, wherein a grain boundary layer in said magnetic recording layer contains a ferromagnetic element, and wherein said crystal grains have a substantially columnar structure and have a magnetic easy axis substantially perpendicular to a substrate surface of said substrate, wherein an adhesion layer comprising an alloy selected from NiTa, NiTaZr, CrTi, CrTiTa, or TiAl, is present between the substrate and the soft magnetic layer,
wherein a ratio of the ferromagnetic element in said grain boundary layer is 30 at. % or more and 50 at. % or less in atomic percent with respect to a solid element which constitutes said grain boundary layer.
2. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said crystal grains have a substantially columnar structure and in an epitaxial relation with the non-magnetic intermediate layer, and have a magnetic easy axis substantially perpendicular to a substrate surface of said substrate.
3. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said substrate is a disk substrate and a ratio of the ferromagnetic element included in said grain boundary layer is a value measured at the most inner circumferential part of the disk where recording is done.
4. The perpendicular magnetic recording medium as claimed in claim 1 , wherein the ratio of the ferromagnetic element included in said grain boundary layer is about 35 at. % or more and about 47 at. % or less in atomic percent with respect to a solid element which constitutes said grain boundary layer.
5. The perpendicular magnetic recording medium as claimed in claim 4 , wherein said substrate is a disk substrate and the ratio of the ferromagnetic element included in said grain boundary layer is a value measured at the most inner circumferential part of the disk where recording is done.
6. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said crystal grains are made of CoCrPt alloy or an alloy whose main component is CoCrPt, and the ferromagnetic element included in said grain boundary layer is Co.
7. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said magnetic recording layer is mainly composed of CoCrPt alloy and Si oxide.
8. The perpendicular magnetic recording medium as claimed in claim 7 , wherein said crystal grains are made of CoCrPt alloy or an alloy whose main component is CoCrPt, and the ferromagnetic element included in said grain boundary layer is Co.
9. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said magnetic recording layer is composed of crystal grains having a hexagonal closed pack structure, and a substantially amorphous grain boundary layer.
10. The perpendicular magnetic recording medium as claimed in claim 1 , wherein an average crystal grain size of said crystal grains of said magnetic recording layer is about 5-8 nm.
11. The perpendicular magnetic recording medium as claimed in claim 1 , wherein an average grain boundary width of said grain boundary layers of said magnetic recording layer is above about 1 nm.
12. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said magnetic recording layer is about 5-30 nm in thickness.
13. The perpendicular magnetic recording medium as claimed in claim 1 , wherein an average size of crystal grains of said non-magnetic intermediate layer is about 6-10 nm.
14. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said non-magnetic intermediate layer is about 2-20 nm in thickness.
15. The perpendicular magnetic recording medium as claimed in claim 1 , wherein said non-magnetic intermediate layer comprises a metal layer and an Ru layer.
16. The perpendicular magnetic recording medium as claimed in claim 15 , wherein said metal layer is about 1 nm in thickness.
17. The perpendicular magnetic recording medium as claimed in claim 1 , further comprising a protective layer disposed on said magnetic recording layer.
18. The perpendicular magnetic recording medium as claimed in claim 17 , wherein said protective layer is mainly composed of C.
19. The perpendicular magnetic recording medium as claimed in claim 17 , wherein said protective layer is about 1-5 nm in thickness.