Multilayer Exchange Spring Recording Media

• US 20070292720A1
• Filed: 06/17/2006
• Published: 12/20/2007
• Est. Priority Date: 06/17/2006
• Status: Active Grant

• Current Assignee: MR Technologies, GmbH
• Original Assignee: Dieter Suess
• Inventors: Suess, Dieter
• Granted Patent: US 9,978,413 B2
• Time in Patent Office: Days
• US Class Current: 428/828.1
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/1207 Testing individual magnetic storage devices, e.g. records carriers or digital storage elements functional testing G06F11/00, G06F11/28
• CPC Class Codes: G11B 5/674 having differing macroscopic or microscopic structures, e.g. differing crystalline lattices, varying atomic structures or differing roughnesses

Abstract

A multilayer exchange spring recording media consists of a magnetically hard magnetic storage layer strongly exchange coupled to a softer nucleation host. The strong exchange coupling can be through a coupling layer or direct. The hard magnetic storage layer has a strong perpendicular anisotropy. The nucleation host consists of one or more ferromagnetic coupled layers. For a multilayer nucleation host the anisotropy increases from layer to layer. The anisotropy in the softest layer of the nucleation host can be two times smaller than that of the hard magnetic storage layer. The lateral exchange between the grains is small. The nucleation host decreases the coercive field significantly while keeping the energy barrier of the hard layer almost unchanged. The coercive field of the total structure depends on one over number of layers in the nucleation host. The invention proposes a recording media that overcomes the writeability problem of perpendicular recording media.

Claims

1. A magnetic recording medium, comprising:

an essentially non-magnetic substrate; and

an exchange coupled magnetic multilayer structure, comprising;

a nucleation host with an anisotropy varying in the film normal direction; and

a hard magnetic storage layer;

wherein the anisotropy assumes more than one value in substantial magnetic portions of the nucleation host.

2. The magnetic recording medium of claim 1, wherein an exchange coupling between the nucleation host and the hard magnetic storage layer is sufficiently strong and the nucleation host is sufficiently hard so that the derivative k of the normalized magnetization with respect to the external field normalized to the coercive field does not change by more than a factor of 3 in a magnetization interval −

0.7<

M_zM_s<

0.7, wherein;

3. The magnetic recording medium of claim 1, wherein the nucleation host and the hard magnetic storage layer are in direct contact.

4. The magnetic recording medium of claim 1, wherein the nucleation host, comprises of ferromagnetic layers with increasing anisotropy from layer to layer.

5. The magnetic recording medium of claim 1, wherein the nucleation host, comprises a ferromagnetic layer with a continuous change of anisotropy in the film normal direction.

6. The magnetic recording medium of claim 1, wherein the nucleation host and the hard magnetic storage layers comprise ferromagnetic layers with increasing anisotropy values.

7. The magnetic recording medium of claim 1, wherein the hard magnetic storage layer comprises at least one of Cr, Pt, Ta, B, Fe, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn and Ni.

8. The magnetic recording medium of claim 1, wherein a coercive field of the nucleation host is less than ½

of a coercive field of the hard magnetic storage layer.

9. The magnetic structure of claim 1 wherein a H_c(α

=20°

)<

H_c(α

=45°

), wherein H_c(α

) is the coercive field if the angle between the external field and the film normal is α

.

10. The magnetic structure of claim 1 wherein a H_m(α

=20°

)<

H_m(α

=45°

), wherein H_m(α

) is the required field to reduce the normalized magnetization from the saturation to −

0.5 if the angle between the external field and the film normal is α

.

11. The magnetic recording medium of claim 1, wherein the nucleation host comprises at least one of Fe, Ni, Al, Si, B, Co, Cr, Pt, Ta, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn, Ni and O.

12. The magnetic recording medium of claim 1, wherein the nucleation host has a thickness smaller than 30 nm.

13. The magnetic recording medium of claim 1, wherein the nucleation host comprises grains with an average diameter greater than 2 nm and less than 10 nm.

14. The magnetic recording medium of claim 1, wherein a height of a plurality of grains is greater than a diameter of the grains.

15. The magnetic recording medium of claim 1, wherein the nucleation host is in direct contact with the hard magnetic storage layer.

16. The magnetic recording medium of claim 1, wherein the nucleation host is separated from the hard magnetic storage layer by a layer of thickness less than 5 nm.

17. The magnetic recording medium of claim 1, wherein the nucleation host is coupled to the hard magnetic storage layer by a strong exchange coupling layer.

18. The magnetic recording medium of claim 1, wherein the nucleation host is coupled to the hard magnetic layer by antiferromagnetic coupling.

19. The magnetic recording medium of claim 1, where parameters of the medium comprise:

a anisotropy constant in the nucleation host Kⁿ₁ as a function of the layer depth

a hard magnetic storage layer anisotropy constant K^h₁;

a nucleation host grain diameter;

a hard magnetic storage layer grain diameter;

an exchange constant between grains in the nucleation host;

an exchange constant between grains of the hard magnetic storage layer;

a saturation polarization in the nucleation host as a function of the layer depth;

a saturation polarization of the hard magnetic storage layer;

a layer thickness of the nucleation host;

a layer thickness of the magnetic storage layer and

an exchange constant between the nucleation host and the hard magnetic layer.

20. The magnetic recording medium of claim 19, wherein a parameter of the magnetic multilayer has a value such that a coercive magnetic field of the hard magnetic storage layer is less than ½

of the coercive magnetic field of the hard magnetic storage layer without the nucleation host.

21. The magnetic recording medium of claim 19, wherein a parameter of the magnetic multilayer has a value such that an energy barrier of a typical grain of the hard magnetic storage layer is smaller at most by 25% of the energy barrier of a typical grain of the hard magnetic storage layer without the nucleation host.

22. The magnetic recording medium of claim 19, wherein an energy barrier of the hard magnetic storage layer is determined by at least one of:

depositing only the hard magnetic storage layer on the non-magnetic substrate;

removing the nucleation host from the multilayer structure;

and performing a micromagnetic calculation with parameters appropriate for the multilayer.

23. The magnetic recording medium of claim 19, wherein a parameter of the magnetic multilayer has a value such that a coercive field of the magnetic multilayer increases when grains of the recording media are misaligned relative to a normal of the non-magnetic substrate.

24. The magnetic recording medium of claim 1, wherein the thickness of the nucleation host has a value such that the in plane component of a magnetization of a remanent state is less than 20% of a total magnetization.

25. The magnetic recording medium of claim 1, wherein the recording medium is usable for at least one of perpendicular recording or recording on patterned elements.

26. A magnetic recording medium, comprising:

an essentially non-magnetic substrate; and

a magnetic bilayer, comprising;

a granular hard magnetic storage layer having a coercive field of H_s without another magnetic layer; and

a granular nucleation host, disposed on the hard magnetic storage layer in a columnar manner, having a coercive field H_n without the hard magnetic storage layer, wherein

0.7 T<

H_n<

H_s; and

the nucleation host is having a magnetic polarization J_s=μ

₀M_s between 0.3 T and 1.0 T, wherein the nucleation host and the hard magnetic storage layer are arranged either in direct contact or separated by a coupling layer of less than 5 nm thickness.

27. The magnetic recording medium of claim 26, wherein the nucleation host and the hard magnetic storage layer are in direct contact.

28. The magnetic recording medium of claim 26, wherein an exchange coupling between the nucleation host and the hard magnetic storage layer is sufficiently strong and the nucleation host is sufficiently hard so that the derivative k of the normalized magnetization with respect to the external field normalized to the coercive field does not change by more than a factor of 3 in a magnetization interval −

0.7<

M_z/M_s<

0.7, wherein;

29. The magnetic recording medium of claim 26, wherein a squareness S of a hysteresis loop is less than 10% different from the squareness of the hysteresis loop of the hard magnetic storage layer without the nucleation host.

30. The magnetic recording medium of claim 26, wherein the hard magnetic storage layer comprises of at least one of Cr, Pt, Ta, B, Fe, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn and Ni.

31. The magnetic structure of claim 26 wherein a H_c(α

=20°

)<

H_c(α

=45°

), wherein H_c(α

) is the coercive field if the angle between the external field and the film normal is α

.

32. The magnetic structure of claim 26 wherein a H_m(α

=20°

)<

H_m(α

=45°

), wherein H_m(α

) is the required field to reduce the normalized magnetization from the saturation to −

0.5 if the angle between the external field and the film normal is α

.

33. The magnetic recording medium of claim 26, wherein the nucleation host comprises at least one of Fe, Ni, Al, Si, B, Co, Cr, Pt, Ta, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn, Ni and O.

34. The magnetic recording medium of claim 26, wherein the nucleation host comprises grains with an average diameter greater than 2 nm and less than 10 nm.

35. The magnetic recording medium of claim 26, wherein the thickness of the nucleation host is larger than 7 nm.

36. The magnetic recording medium of claim 26, wherein the nucleation host is in direct contact with the hard magnetic storage layer.

37. The magnetic recording medium of claim 26, wherein the nucleation host is coupled to the hard magnetic storage layer by a strong exchange coupling layer.

38. The magnetic recording medium of claim 26, wherein the nucleation host is coupled to the hard magnetic storage layer by an antiferromagnetic coupling.

39. The magnetic recording medium of claim 26, where parameters of the media structure comprise:

a anisotropy constant in the nucleation host Kⁿ₁

a hard magnetic storage layer anisotropy constant Kⁿ₁;

a nucleation host grain diameter;

a hard magnetic storage layer grain diameter;

an exchange constant between grains in the nucleation host;

an exchange constant between grains of the hard magnetic storage layer;

a saturation polarization in the nucleation host as a function of the layer depth;

a saturation polarization of the hard magnetic storage layer;

a layer thickness of the nucleation host;

a layer thickness of the magnetic storage layer and

an exchange constant between the nucleation host and the hard magnetic storage layer.

40. The magnetic recording medium of claim 39, wherein the coercive field of the hard magnetic storage layer is determined by at least one of:

depositing only the hard magnetic storage on the non-magnetic substrate;

removing the nucleation host from a multilayer structure; and

performing a micromagnetic calculation with parameters appropriate for the multilayer.

41. The magnetic recording medium of claim 39, wherein an energy barrier of the hard magnetic storage layer is determined by at least one of:

depositing only the hard magnetic storage layer on the non-magnetic substrate;

removing the nucleation host from the multilayer structure;

and performing a micromagnetic calculation with parameters appropriate for the multilayer.

42. The magnetic recording medium of claim 39, wherein a parameter of the magnetic bilayer has a value such that a coercive magnetic field of the hard magnetic storage layer is less than ½

of the coercive magnetic field of the hard magnetic storage layer without the nucleation host.

43. The magnetic recording medium of claim 39, wherein a parameter of the magnetic recording medium has a value such that a coercive field of the magnetic recording medium increases when grains of the recording media are misaligned relative to a normal of the non-magnetic substrate.

44. The magnetic recording medium of claim 26, wherein the recording medium is usable for perpendicular recording or for recording on patterned elements.

45. A magnetic recording medium, comprising:

an essentially non-magnetic substrate; and

an exchange coupled magnetic multilayer structure, comprising;

a nucleation host with an anisotropy varying in the film normal direction; and

a hard magnetic storage layer;

wherein a ratio