Magnetic stack having assist layer

• US 7,936,598 B2
• Filed: 04/28/2009
• Issued: 05/03/2011
• Est. Priority Date: 04/28/2009
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology plc (Seagate Technology Holdings Plc)
• Inventors: Zheng, Yuankai, Feng, Xuebing, Gao, Zheng, Xi, Haiwen, Jung, Wonjoon, Lou, Xiaohua
• Primary Examiner(s): NGUYEN, TAN
• Application Number:
  US12/431,162
• Publication Number:
  US 20100271870A1
• Time in Patent Office: 735 Days
• Field of Search: 365/22, 365/55
• US Class Current: 365/173
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• CPC Class Codes: H01F 10/3263 the exchange coupling being symmetric, e.g. for dual spin valve, e.g. NiO/Co/Cu/Co/Cu/Co/NiO
• CPC Class Codes: H01F 10/3286 Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
• CPC Class Codes: H01F 10/329 Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect
• CPC Class Codes: H01F 10/3295 Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: H10N 50/80 Constructional details

Abstract

A magnetic memory cell having a ferromagnetic free layer and a ferromagnetic pinned reference layer, each having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation and switchable by spin torque. The cell includes a ferromagnetic assist layer proximate the free layer, the assist layer having a low magnetic anisotropy less than about 500 Oe. The assist layer may have in-plane or out-of-plane anisotropy.

Claims

1. A magnetic cell comprising:

a ferromagnetic free layer and a first ferromagnetic pinned reference layer, each having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation and switchable by spin torque;

a first oxide barrier layer between the free layer and the reference layer; and

a ferromagnetic assist layer having low magnetic anisotropy less than 500 Oe proximate the free layer.

2. The magnetic cell of claim 1 wherein the assist layer has in-plane magnetic anisotropy.

3. The magnetic cell of claim 1 wherein the assist layer has out-of-plane magnetic anisotropy.

4. The magnetic cell of claim 1 wherein the assist layer comprises at least one of Co, Ni, Fe or an alloy thereof.

5. The magnetic cell of claim 1 wherein the assist layer has a magnetic moment of less than about 1000 emu/cc.

6. The magnetic cell of claim 1 further comprising a second pinned reference layer having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation, the assist layer positioned between the free layer and the second reference layer.

7. The magnetic cell of claim 6 further comprising a first enhancement layer and a second enhancement layer, the first enhancement layer between the oxide barrier layer and the free layer and the second enhancement layer between the oxide barrier layer and the first reference layer.

8. The magnetic cell of claim 7 further comprising a third enhancement layer proximate the second reference layer.

9. The magnetic cell of claim 8 further comprising a second oxide barrier layer between the assist layer and the third enhancement layer.

10. The magnetic cell of claim 6 comprising a conductive non-ferromagnetic spacer layer between the assist layer and the free layer.

11. The magnetic cell of claim 6 comprising an electrically insulative spacer layer between the assist layer and the free layer.

12. The magnetic cell of claim 6 wherein upon passage of a current through the magnetic cell, the magnetization orientation of the assist layer is at least 10 degrees from in-plane.

13. The magnetic cell of claim 6 wherein the magnetic cell is a magnetic tunnel junction memory cell.

14. A magnetic memory cell on a substrate, the memory cell comprising:

a ferromagnetic free layer having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation perpendicular to the substrate and switchable by spin torque;

a first ferromagnetic pinned reference layer having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation perpendicular to the substrate;

an oxide barrier layer between the free layer and the first reference layer; and

a ferromagnetic assist stack proximate the free layer having low magnetic anisotropy, the assist stack comprising an assist layer having a magnetic moment less than 1000 emu/cc and a magnetization orientation that rotates in a direction of electron flow from a current.

15. The memory cell of claim 14 wherein the assist layer has in-plane magnetic anisotropy.

16. The memory cell of claim 15 wherein the magnetization orientation of the assist layer is at least 10 degrees from in-plane.

17. The memory cell of claim 14 wherein the assist layer has a low magnetic anisotropy less than about 500 Oe.

18. A method of writing to a magnetic cell comprising:

passing a current through a magnetic cell comprising a free layer and a reference layer, each having an out-of-plane anisotropy and magnetization orientation, the current having an electron flow direction;

rotating a magnetization orientation of an assist layer proximate the free layer in the electron flow direction, the assist layer having a magnetic anisotropy less than 500 Oe; and

orienting the magnetization orientation of the free layer in the electron flow direction.

19. The method of claim 18 further comprising:

passing the current through a second reference layer having an out-of-plane anisotropy and magnetization orientation.

20. The method of claim 18 wherein rotating a magnetization orientation of an assist layer comprises rotating the magnetization orientation at least 10 degrees from in-plane.