Spin-torque magnetoresistive structures

1. A magnetoresistive structure comprising:

a first pinned ferromagnetic layer;

a first nonmagnetic spacer layer in physical contact with the first pinned ferromagnetic layer;

a second free ferromagnetic layer in physical contact with the first nonmagnetic spacer layer;

a first free antiferromagnetic layer in physical contact with the second free ferromagnetic layer;

a second nonmagnetic spacer layer in physical contact with the first free antiferromagnetic layer;

a second pinned antiferromagnetic layer in physical contact with the second nonmagnetic spacer layer;

a third pinned ferromagnetic layer in physical contact with the second pinned antiferromagnetic layer; and

a third pinned antiferromagnetic layer in physical contact with the first pinned ferromagnetic layer,

wherein the third pinned ferromagnetic layer and the third pinned antiferromagnetic layer are terminal layers of the magnetoresistive structure.

2. The magnetoresistive structure of claim 1 , wherein the first nonmagnetic spacer layer comprises at least one of a tunneling barrier layer, magnesium oxide, and a nonmagnetic metallic layer.

3. The magnetoresistive structure of claim 1 , wherein the second nonmagnetic spacer layer comprises at least one of a nonmagnetic metallic layer and a giant magnetoresistance layer.

4. The magnetoresistive structure of claim 1 , wherein at least one of: i) the first free antiferromagnetic layer comprises chromium, ii) the second pinned antiferromagnetic layer comprises chromium, and iii) the second nonmagnetic spacer layer comprises at least one of gold, copper and ruthenium.

5. The magnetoresistive structure of claim 1 , wherein the second free ferromagnetic layer is exchange coupled to the first free antiferromagnetic layer.

6. The magnetoresistive structure of claim 1 , wherein at least one of the first free antiferromagnetic layer, the second nonmagnetic spacer layer, and the second pinned antiferromagnetic layer are adapted to provide a majority of spin-torque for switching magnetic polarization of the second free ferromagnetic layer.

7. The magnetoresistive structure of claim 1 , wherein the second pinned antiferromagnetic layer is pinned by at least one of i) the third pinned ferromagnetic layer, and ii) the second pinned antiferromagnetic layer being thicker than the first free antiferromagnetic layer.

8. The magnetoresistive structure of claim 1 , wherein at least one of the first pinned ferromagnetic layer and the third pinned ferromagnetic layer comprises at least one of: i) an alloy of cobalt and iron, and ii) a plurality of sub-layers, wherein two of the plurality of sub-layers have anti-parallel magnetic moments.

9. The magnetoresistive structure of claim 1 , wherein the second free ferromagnetic layer comprises an alloy comprising at least one of iron, cobalt, and nickel.

10. The magnetoresistive structure of claim 1 , wherein at least one of the first free antiferromagnetic layer, the second pinned antiferromagnetic layer and the third pinned antiferromagnetic layer comprises an alloy, and wherein the alloy comprises at least one member selected from a group consisting of manganese, iridium, nickel, platinum and iron.

11. The magnetoresistive structure of claim 1 adapted for switching of magnetic moments of both the second free ferromagnetic layer and the first free antiferromagnetic layer by a write current.

12. The magnetoresistive structure of claim 1 , wherein the magnitude of a write current necessary to switch a magnetic moment of the second free ferromagnetic layer is less than a comparison write current necessary to switch a comparison magnetic moment of a comparison free ferromagnetic layer in a comparison magnetoresistive structure comprising the comparison free ferromagnetic layer abutted on one side by a comparison nonmagnetic spacer layer and abutted on another side by at least one of a device terminal, another comparison nonmagnetic spacer layer and a comparison ferromagnetic layer.

13. The magnetoresistive structure of claim 1 , wherein the first free antiferromagnetic layer is adapted to provide thermal stability for the second free ferromagnetic layer.

14. A magnetoresistive memory device comprising:

a first pinned ferromagnetic layer;

a first nonmagnetic spacer layer in physical contact with the first pinned ferromagnetic layer;

a second free ferromagnetic layer in physical contact with the first nonmagnetic spacer layer;

a first free antiferromagnetic layer in physical contact with the second free ferromagnetic layer;

a second nonmagnetic spacer layer in physical contact with the first free antiferromagnetic layer;

a second pinned antiferromagnetic layer in physical contact with the second nonmagnetic spacer layer;

a third pinned ferromagnetic layer in physical contact with the second pinned antiferromagnetic layer; and

a third pinned antiferromagnetic layer in physical contact with the first pinned ferromagnetic layer,

wherein the third pinned ferromagnetic layer and the third pinned antiferromagnetic layer are terminal layers of the magnetoresistive structure, and

wherein the magnetoresistive memory device stores at least two data states corresponding to at least two directions of a magnetic moment.

15. The magnetoresistive memory device of claim 14 , wherein at least one of the first free antiferromagnetic layer, the second nonmagnetic spacer layer, and the second pinned antiferromagnetic layer are adapted to provide a majority of spin-torque for switching magnetic polarization of the second free ferromagnetic layer.

16. The magnetoresistive memory device of claim 14 , wherein data stored within a memory cell corresponds to the direction of a magnetic moment in at least one of the second free ferromagnetic layer and the first free antiferromagnetic layer.

17. An integrated circuit comprising:

a substrate;

a first pinned ferromagnetic layer;

a first nonmagnetic spacer layer in physical contact with the first pinned ferromagnetic layer;

a second free ferromagnetic layer in physical contact with the first nonmagnetic spacer layer;

a first free antiferromagnetic layer in physical contact with the second free ferromagnetic layer;

a second nonmagnetic spacer layer in physical contact with the first free antiferromagnetic layer;

a second pinned antiferromagnetic layer in physical contact with the second nonmagnetic spacer layer;

a third pinned ferromagnetic layer in physical contact with the second pinned antiferromagnetic layer; and

a third pinned antiferromagnetic layer in physical contact with the first pinned ferromagnetic layer,

wherein the third pinned ferromagnetic layer and the third pinned antiferromagnetic layer are terminal layers of the magnetoresistive structure.

18. The integrated circuit of claim 17 , wherein at least one of the first free antiferromagnetic layer, the second nonmagnetic spacer layer, and the second pinned antiferromagnetic layer are adapted to provide a majority of spin-torque for switching magnetic polarization of the second free ferromagnetic layer.

19. A method for forming a spin-torque structure, the method comprising the steps of:

forming a first pinned ferromagnetic layer;

forming a first nonmagnetic spacer layer in physical contact with the first pinned ferromagnetic layer;

forming a second free ferromagnetic layer in physical contact with the first nonmagnetic spacer layer;

forming a first free antiferromagnetic layer in physical contact with the second free ferromagnetic layer;

forming a second nonmagnetic spacer layer in physical contact with the first free antiferromagnetic layer;

forming a second pinned antiferromagnetic layer in physical contact with the second nonmagnetic spacer layer;

forming a third pinned ferromagnetic layer in physical contact with the second pinned antiferromagnetic layer; and

forming a third pinned antiferromagnetic layer in physical contact with the first pinned ferromagnetic layer,

wherein the third pinned ferromagnetic layer and the third pinned antiferromagnetic layer are terminal layers of the magnetoresistive structure.