Composite free layer for magnetoresistive random access memory

1. An apparatus comprising:

a magnetic tunnel junction for storing data, the magnetic tunnel junction comprising a fixed layer, a barrier layer, and a composite free layer, the barrier layer disposed between the fixed layer and the composite free layer, the composite free layer comprising:

an in-plane anisotropy free layer;

a perpendicular magnetic anisotropy (PMA) inducing layer disposed such that the in-plane anisotropy free layer is between the barrier layer and the PMA-inducing layer, the PMA-inducing layer reducing an effective magnetization of the composite free layer; and

a ferromagnetic amorphous layer disposed between the in-plane anisotropy free layer and the PMA-inducing layer.

2. The apparatus of claim 1 , wherein the ferromagnetic amorphous layer comprises an alloy of cobalt, titanium, and boron.

3. The apparatus of claim 1 , wherein the ferromagnetic amorphous layer comprises an alloy of cobalt, iron, boron, and tantalum.

4. The apparatus of claim 1 , wherein a thickness of the PMA-inducing layer is selected such that a total magnetic moment of the composite free layer is in-plane.

5. The apparatus of claim 1 , wherein the PMA-inducing layer reduces the effective magnetization of the composite free layer by a factor of five to ten.

6. The apparatus of claim 1 , wherein the PMA-inducing layer comprises one or more of a superlattice of alternating cobalt and platinum layers, a rare earth and transition metal alloy, and an L1 0 -phase alloy.

7. The apparatus of claim 1 , wherein PMA-inducing layer comprises a superlattice of alternating cobalt and platinum layers, the superlattice comprising three cobalt layers and three platinum layers.

8. The apparatus of claim 1 , wherein the ferromagnetic amorphous layer comprises an alloy of one or more ferromagnetic elements, one or more glass-forming elements, and one or more stabilizing elements for preventing migration of the one or more glass-forming elements.

9. The apparatus of claim 8 , wherein the one or more ferromagnetic elements comprise one or more of iron and cobalt, the one or more glass-forming elements comprise boron, and the one or more stabilizing elements comprise one or more of tantalum and titanium.

10. The apparatus of claim 8 , wherein the alloy comprises ten atomic percent or more of the one or more glass-forming elements, and five atomic percent or less of the one or more stabilizing elements.

11. The apparatus of claim 1 , further comprising a spin Hall effect layer configured such that an in-plane electric current within the spin Hall effect layer causes a spin current in the composite free layer.

12. The apparatus of claim 11 , wherein the PMA-inducing layer reduces a current density for the in-plane electric current to between one million and ten million amperes per square centimeter.

13. A system comprising:

a magnetoresistive random access memory (MRAM) die, the MRAM die comprising a plurality of magnetic tunnel junctions, wherein a magnetic tunnel junction comprises a reference layer, a barrier layer, and a composite free layer, the barrier layer disposed between the reference layer and the composite free layer, the composite free layer comprising:

an in-plane anisotropy free layer in contact with the barrier layer;

a ferromagnetic amorphous layer in contact with the in-plane anisotropy free layer; and

a perpendicular magnetic anisotropy (PMA) inducing layer in contact with the ferromagnetic amorphous layer, the PMA-inducing layer reducing a current density for an in-plane current within a spin Hall effect layer.

14. The system of claim 13 , wherein a thickness of the PMA-inducing layer is selected such that the PMA-inducing layer reduces an effective magnetization of the composite free layer, and such that a total magnetic moment of the composite free layer is in-plane.

15. The system of claim 13 , wherein a magnetic tunnel junction is coupled to the spin Hall effect layer such that the in-plane electric current within the spin Hall effect layer causes a spin current in the composite free layer.

16. The system of claim 13 , wherein the ferromagnetic amorphous layer comprises an alloy of one or more ferromagnetic elements, one or more glass-forming elements, and one or more stabilizing elements for preventing migration of the one or more glass-forming elements.

17. The system of claim 16 , wherein the one or more ferromagnetic elements comprise one or more of iron and cobalt, the one or more glass-forming elements comprise boron, and the one or more stabilizing elements comprise one or more of tantalum and titanium.

18. The system of claim 16 , wherein the alloy comprises ten atomic percent or more of the one or more glass-forming elements, and five atomic percent or less of the one or more stabilizing elements.

19. An apparatus comprising:

means for storing data in a composite free layer for a magnetic tunnel junction, based on an orientation of an in-plane magnetic moment for the composite free layer;

means for permanently inducing a perpendicular magnetic anisotropy (PMA) for the composite free layer, the means for permanently inducing a PMA reducing an effective magnetization of the composite free layer

means for separating the means for storing data from the means for permanently inducing a PMA, such that a crystal structure of the means for storing data is unaffected by the means for permanently inducing a PMA.

20. The apparatus of claim 19 , further comprising means for producing a spin current to change the orientation of the in-plane magnetic moment for the composite free layer.