Biasing for tri-layer magnetoresistive sensors

• US 20050088789A1
• Filed: 10/27/2003
• Published: 04/28/2005
• Est. Priority Date: 10/27/2003
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Linville, Eric S., Xue, Song S., He, Qing, Heinonen, Olle, Mao, Sining, Tang, Xuefei, Singleton, Eric W., Hou, Chunhong
• Granted Patent: US 7,177,122 B2
• Time in Patent Office: Days
• US Class Current: 360/324.120
• CPC Class Codes: G11B 2005/0018 by current biasing control or regulation
• CPC Class Codes: G11B 2005/3996 large or giant magnetoresistive effects [GMR], e.g. as generated in spin-valve [SV] devices
• CPC Class Codes: G11B 5/3909 Arrangements using a magnetic tunnel junction
• CPC Class Codes: G11B 5/3932 Magnetic biasing films

Abstract

A biasing system for a tri-layer reader stack magnetoresistive sensor is disclosed. The tri-layer reader stack includes a first ferromagnetic free layer, a second ferromagnetic free layer, and a magnetoresistive layer between the first and second ferromagnetic free layers. The free layers are positioned in the tri-layer reader stack such that quiescent state magnetizations of the free layers are antiparallel. A biasing layer is positioned with regard to the tri-layer reader stack, typically separated from the tri-layer reader stack by a nonmagnetic spacer layer. A biasing means is positioned such that a magnetization of the biasing layer is perpendicular to the quiescent state magnetizations of the free layers. This biasing results in the free layers having biased magnetizations directed substantially orthogonal with respect to each other.

Claims

1. A magnetoresistive sensor comprising:

a tri-layer reader stack including a first ferromagnetic layer, a second ferromagnetic layer, and a magnetoresistive layer positioned therebetween; and

biasing means positioned with respect to the tri-layer reader stack for biasing a magnetization of the first ferromagnetic layer substantially orthogonal to a magnetization of the second ferromagnetic layer.

2. The magnetoresistive sensor of claim 1, further comprising:

nonmagnetic spacer means positioned between the tri-layer stack and the biasing means.

3. The magnetoresistive sensor of claim 2, wherein the nonmagnetic spacer means is made of a material which enhances specular electron scattering.

4. The magnetoresistive sensor of claim 1, wherein the magnetization of the first ferromagnetic layer is antiparallel to the magnetization of the second ferromagnetic layer in a quiescent state.

5. The magnetoresistive sensor of claim 4, wherein the quiescent state magnetization of the first and second ferromagnetic layers are antiparallel due to shape anisotropy.

6. The magnetoresistive sensor of claim 4, wherein a biasing direction of the biasing means is generally perpendicular to the magnetization of the first and second ferromagnetic layers in the quiescent state.

7. The magnetoresistive sensor of claim 1, wherein the magnetization of the first ferromagnetic layer and the magnetization of the second ferromagnetic layer rotate in response to flux emanated from a rotating disc.

8. The magnetoresistive sensor of claim 1, wherein the biasing means is at least one permanent magnet layer having a shape anisotropy induced magnetization direction.

9. The magnetoresistive sensor of claim 1, wherein the biasing means is at least one permanent magnet layer comprising a high coercivity ferromagnetic material.

10. The magnetoresistive sensor of claim 1, wherein the biasing means is a layer of antiferromagnetic material.

11. The magnetoresistive sensor of claim 1, wherein the biasing means is a bilayer including a layer of antiferromagnetic material and a layer of ferromagnetic material.

12. The magnetoresistive sensor of claim 1, wherein the biasing means produces a sense current induced magnetic field.

13. The magnetoresistive sensor of claim 1, wherein the biasing means is an antiferromagnetic/ferromagnetic/antiferromagnetic stack.

14. The magnetoresistive sensor of claim 1, wherein the magnetoresistive layer is a nonmagnetic metal.

15. The magnetoresistive sensor of claim 1, wherein the magnetoresistive layer is a tunnel barrier.

16. A magnetoresistive sensor having an air bearing surface for confronting a surface of a rotating disc comprising:

a first ferromagnetic free layer;

a second ferromagnetic free layer having a quiescent state magnetization substantially antiparallel to a quiescent state magnetization of the first ferromagnetic free layer;

a magnetoresistive layer located between the first and second ferromagnetic free layers; and

at least one biasing structure positioned with respect to the first and second ferromagnetic free layers to bias a magnetization of the first ferromagnetic free layer substantially orthogonal to a magnetization of the second ferromagnetic free layer.

17. The magnetoresistive sensor of claim 16, wherein the at least one biasing structure is a permanent magnet.

18. The magnetoresistive sensor of claim 17, wherein the permanent magnet is made of a material selected from the group consisting of CoCrPt, CoPt and a CoPt/SiO₂ composite.

19. The magnetoresistive sensor of claim 16, wherein the at least one biasing structure is a soft bias antiferromagnetic/ferromagnetic/antiferromagnetic multilayer structure.

20. The magnetoresistive sensor of claim 19, wherein the antiferromagnetic layers are made of a material selected from the group consisting of IrMn, NiO, and Fe₃O₄, and wherein the ferromagnetic layer is made of a material selected from the group consisting of CoFe, Fe₂O₃, and a CoFe/HfO composite.

21. The magnetoresistive sensor of claim 16, wherein a magnetization of the at least one biasing structure is generally perpendicular to the quiescent state magnetization of the first and second ferromagnetic free layers.

22. The magnetoresistive sensor of claim 16, wherein the magnetization of the first ferromagnetic free layer and the magnetization of the second ferromagnetic free layer rotate in response to flux emanated from the rotating disc.

23. The magnetoresistive sensor of claim 16, wherein the magnetoresistive layer is a metal.

24. The magnetoresistive sensor of claim 16, wherein the magnetoresistive layer is a tunnel barrier.

25. The magnetoresistive sensor of claim 16, wherein the at least one biasing structure is separated from the first and second ferromagnetic free layers by a nonmagnetic spacer layer.

26. The magnetoresistive sensor of claim 25, wherein the nonmagnetic spacer layer is made of a material which enhances specular electron scattering.

27. A magnetoresistive sensor comprising:

a tri-layer reader stack including a first ferromagnetic layer, a second ferromagnetic layer, and a nonmagnetic layer positioned therebetween; and

current leads positioned on a top and a bottom of the tri-layer reader stack such that magnetic fields produced by a current passed through the current leads biases a magnetization of the first ferromagnetic layer substantially orthogonal to a magnetization of the second ferromagnetic layer.