Magnetic recording medium and magnetic storage apparatus

• US 6,610,424 B1
• Filed: 11/22/2000
• Issued: 08/26/2003
• Est. Priority Date: 04/07/2000
• Status: Expired due to Fees

• Current Assignee: Showa Denko KK
• Original Assignee: Fujitsu Limited
• Inventors: Acharya, B. Ramamurthy, Abarra, E. Noel
• Primary Examiner(s): RICKMAN, HOLLY C
• Application Number:
  US09/721,097
• Time in Patent Office: 1,007 Days
• Field of Search: 428/694.TM, 428/694.TS, 428/336, 428/212, 428/900
• US Class Current: 428/830
• CPC Class Codes: G11B 5/00 Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor G11B11/00 and G11B13/00 take precedence
• CPC Class Codes: G11B 5/64 comprising only the magnetic material without bonding agent
• CPC Class Codes: G11B 5/66 the record carriers consisting of several layers
• CPC Class Codes: G11B 5/672 having different compositions in a plurality of magnetic layers, e.g. layer compositions having differing elemental components or differing proportions of elements
• CPC Class Codes: Y10S 428/90 Magnetic feature
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/265 1 mil or less

Abstract

A magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate, is characterized by the magnetic layer which includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer. A saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfies a relationship M_Sa<M_Stot<M_Sb or M_Sa>M_Stot>M_Sb.

Claims

1. A magnetic recording medium comprising:

a substrate; and

a magnetic layer disposed above the substrate,

wherein said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer, and

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa<

M_Stot<

M_Sb,

said initial layer is made of a CoCrB_y alloy where y denotes an At % content satisfying 1<

y<

15, and said final layer is made of a CoCrB_z alloy where z denotes an At % content satisfying 0≦

z<

10.

2. The magnetic recording medium as claimed in claim 1, wherein said magnetic layer as a whole has a signal-to-noise ratio higher than that obtained solely by the initial layer and also higher than that obtained solely by the final layer.

3. The magnetic recording medium as claimed in claim 1, wherein said magnetic layer as a whole has a coercivity higher than a coercivity of a medium solely made up of an equally thick initial layer and lower than a coercivity of a medium solely made up of an equally thick final layer.

4. The magnetic recording medium as claimed in claim 1, wherein said initial layer has a thickness in a range of 1 to 10 nm, and said final layer has a thickness in a range of 1 to 10 nm.

5. The magnetic recording medium as claimed in claim 1, wherein said initial layer is made of a CoCr_x1B_y1 alloy where x1 denotes an At % content satisfying 15<

x1<

27 and yl denotes an At % content satisfying 1<

y1<

15, and said final layer is made of a CoCr_x2B_y2 alloy where x2 denotes an At % content satisfying 10<

x2<

24 and y2 denotes an At % content satisfying 0≦

y2<

10.

6. The magnetic recording medium as claimed in claim 1, wherein said magnetic layer as a whole has a thermal stabilization factor KuV/kT higher than that of a single layer solely made of the initial layer, where Ku denotes magnetic anisotropy, V denotes volume of grain, T denotes temperature, and k denotes Boltzmann constant.

7. The magnetic recording medium as claimed in claim 1, wherein said magnetic layer has a grain diameter smaller than that of a layer made up solely of the final layer and having a thickness equal to a total thickness of the magnetic layer.

8. The magnetic recording medium as claimed in claim 1, wherein said initial layer is made of a material selected from a group consisting of CoCrB_y, CoCrTaB_y, CoCrPtB_y, CoCrPtB_yCu, CoCrPtTaB_y and alloys thereof, and said final layer is made of a material selected from a group consisting of CoCrB_z, CoCrTaB_z, CoCrPtB_z, CoCrPtB_zCu, CoCrPtTaB_z, CoCrPtWB_z, CoCrPtTaNbB_z and alloys thereof.

9. A magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate, characterized in that:

said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb,

wherein said magnetic layer as a whole has a signal-to-noise ratio higher than that obtained solely by the initial layer and also higher than that obtained solely by the final layer.

11. The magnetic recording medium as claimed in claim 9, wherein said initial layer has a thickness in a range of 1 to 10 nm, and said final layer has a thickness in a range of 1 to 10 nm.

12. The magnetic recording medium as claimed in claim 9, wherein said initial layer is made of a CoCr_x1 alloy where x1 denotes an At % content satisfying 15<

x1<

27, and said final layer is made of a CoCr_x2 alloy where x denotes an At % content satisfying 10<

x2<

24.

14. The magnetic recording medium as claimed in claim 9, wherein said magnetic layer as a whole has a thermal stabilization factor KuV/kT higher than that of a single layer solely made of the initial layer, where Ku denotes magnetic anisotropy, V denotes volume of grain, T denotes temperature, and k denotes Boltzmann constant.

16. The magnetic recording medium as claimed in claim 9, wherein said initial layer and said final layer are respectively made of a material selected from a group consisting of CoCr, CoCrTa, CoCrPt, CoCrPtB, CoCrPtBCu, CoCrPtTa, CoCrPtTaB, CoCrPtW, CoCrPtTaNb and alloys thereof.

10. A magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate, characterized in that:

said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb,

wherein said magnetic layer as a whole has a coercivity higher than a coercivity of a medium solely made of an equally thick initial layer and lower than a coercivity of a medium solely made of an equally thick final layer.

19. The magnetic recording medium as claimed in claim 10 wherein said initial layer has a thickness in a range of 1 to 10 nm, and said final layer has a thickness in a range of 1 to 10 nm.

20. The magnetic recording medium as claimed in claim 10, wherein said initial layer is made of a CoCr_x1 alloy where x1 denotes an At % content satisfying 15<

x1<

27, and said final layer is made of a CoCr_x2 alloy where x2 denotes an At % content satisfying 10<

x2<

24.

21. The magnetic recording medium as claimed in claim 10, wherein said magnetic layer as a whole has a thermal stabilization factor KuV/kT higher than that of a single layer solely made of the initial layer, where Ku denotes magnetic anisotropy, V denotes volume of grain, T denotes temperature, and k denotes Boltzmann constant.

22. The magnetic recording medium as claimed in claim 10, wherein said initial layer and said final layer are respectively made of a material selected from a group consisting of CoCr, CoCrTa, CoCrPt, CoCrPtB, CoCrPtBCu, CoCrPtTa, CoCrPtTaB, CoCrPtW, CoCrPtTaNb and alloys thereof.

13. A magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate, characterized in that:

said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb,

wherein said initial layer is made of a CoCrB_y alloy where y denotes an At % content satisfying 1<

y<

15, and said final layer is made of a CoCrB_z alloy where z denotes an At % content satisfying 0≦

z<

10.

23. The magnetic recording medium as claimed in claim 13, wherein said initial layer has a thickness in a range of 1 to 10 nm, and said final layer has a thickness in a range of 1 to 10 nm.

24. The magnetic recording medium as claimed in claim 13, wherein said magnetic layer as a whole has a thermal stabilization factor KuV/kT higher than that of a single layer solely made of the initial layer, where Ku denotes magnetic anisotropy, V denotes volume of grain, T denotes temperature, and k denotes Boltzmann constant.

15. A magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate, characterized in that:

said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb,

wherein said magnetic layer has a gain diameter smaller than that of a layer made up solely of the final layer and having a thickness equal to a total thickness of the magnetic layer.

25. The magnetic recording medium as claimed in claim 15, wherein said initial layer has a thickness in a range of 1 to 10 nm, and said final layer has a thickness in a range of 1 to 10 nm.

26. The magnetic recording medium as claimed in claim 15, wherein said initial layer is made of a CoCr_x1 alloy where x1 denotes an At % content satisfying 15<

x1<

27, and said final layer is made of a CoCr_x2 alloy where x2 denotes an At % content satisfying 10<

x2<

24.

27. The magnetic recording medium as claimed in claim 15, wherein said magnetic layer as a whole has a thermal stabilization factor KuV/kT higher than that of a single layer solely made of the initial layer, where Ku denotes magnetic anisotropy, V denotes volume of grain, T denotes temperature, and k denotes Boltzmann constant.

28. The magnetic recording medium as claimed in claim 15, wherein said initial layer and said final layer are respectively made of a material selected from a group consisting of CoCr, CoCrTa, CoCrPt, CoCrPtB, CoCrPtBCu, CoCrPtTa, CoCrPtTaB, CoCrPtW, CoCrPtTaNb, and alloys thereof.

17. A magnetic storage apparatus comprising:

a head; and

at least one magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate,

wherein said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer, and

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa<

M_Stot<

M_Sb or M_Sa>

M_Stot>

M_Sb,

said initial layer being made of a CoCrB_y alloy where y denotes an At % content satisfying 1<

y<

15, and said final layer is made of a CoCrB_z alloy where z denotes an At % content satisfying 0≦

z<

10.

18. The magnetic storage apparatus as claimed in claim 17, wherein said magnetic layer as a whole has a signal-to-noise ratio higher than that obtained solely by the initial layer and also higher than that obtained solely by the final layer.

29. A magnetic storage apparatus comprising:

a head; and

at least one magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate,

wherein said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb, and

said magnetic layer as a whole has a signal-to-noise ratio higher than that obtained solely by the initial layer and also higher than that obtained solely by the final layer.

30. A magnetic storage apparatus comprising:

a head; and

at least one magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate,

wherein said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb, and

said magnetic layer as a whole has a coercivity higher than a coercivity of a medium solely made of an equally thick initial layer and lower than a coercivity of a medium solely made of an equally thick final layer.

31. A magnetic storage apparatus comprising:

a head; and

at least one magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate,

wherein said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb, and

said initial layer is made of a CoCrB_y alloy where y denotes an At % content satisfying 1<

y<

15, and said final layer is made of a CoCrB_z alloy where z denotes an At % content satisfying 0≦

z<

10.

32. A magnetic storage apparatus comprising:

a head; and

at least one magnetic recording medium provided with a substrate and a magnetic layer disposed above the substrate,

wherein said magnetic layer includes an initial layer located closer to the substrate and a final layer located further away from the substrate than the initial layer,

a saturation magnetization M_Sa of the initial layer, a saturation magnetization M_Sb of the final layer, and a saturation magnetization M_Stot of the magnetic layer as a whole satisfy a relationship M_Sa>

M_Stot>

M_Sb, and

said magnetic layer has a grain diameter smaller than that of a layer made up solely of the final layer and having a thickness equal to a total thickness of the magnetic layer.