Magnetic stack having assist layer
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.
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.