STRAM with composite free magnetic element
Spin-transfer torque memory includes a composite free magnetic element, a reference magnetic element having a magnetization orientation that is pinned in a reference direction, and an electrically insulating and non-magnetic tunneling barrier layer separating the composite free magnetic element from the magnetic reference element. The free magnetic element includes a hard magnetic layer exchanged coupled to a soft magnetic layer. The composite free magnetic element has a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit.
1. A spin-transfer torque memory unit, comprising:
a free magnetic element comprising a hard magnetic layer exchanged coupled to a soft magnetic layer, the hard magnetic layer has a saturation moment of less than 1000 emu/cm 3 and a coercively value that is equal to or greater than 1000 Oersteds, the free magnetic element having a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit;
a reference magnetic element having a magnetization orientation that is pinned in a reference direction; and
an electrically insulating and non-magnetic tunneling barrier layer separating the free magnetic element from the magnetic reference element.
2. A spin-transfer torque memory unit according to claim 1 , wherein the soft magnetic layer has a spin polarization value greater than 0.5.
3. A spin-transfer torque memory unit according to claim 1 , wherein the hard magnetic layer has uniaxial magnetic anisotropy.
4. A spin-transfer torque memory unit according to claim 1 , wherein the free magnetic element has an aspect ratio of 1.
5. A spin-transfer torque memory unit according to claim 1 , wherein the soft magnetic layer has a coercively value that is equal to or less than 500 Oersteds.
6. A spin-transfer torque memory unit according to claim 1 , wherein the hard magnetic layer has a saturation moment of less than 500 emu/cm 3 .
7. A spin-transfer torque memory unit, comprising:
a free magnetic element comprising a granular hard magnetic layer exchanged coupled to a soft magnetic layer, the soft magnetic layer having a coercivity value less than 500 Oersteds, the granular hard magnetic layer comprising a plurality of hard magnetic particles separated by non-magnetic material, the free magnetic element having a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit;
a reference magnetic element having a magnetization orientation that is pinned in a reference direction; and
an electrically insulating and non-magnetic tunneling barrier layer separating the free magnetic element from the magnetic reference element.
8. A spin-transfer torque memory unit according to claim 7 , wherein the soft magnetic layer has a spin polarization value greater than 0.5.
9. A spin-transfer torque memory unit according to claim 7 , wherein the hard magnetic particles have uniaxial magnetic anisotropy and a coercively value greater than 1000 Oersteds.
10. A spin-transfer torque memory unit according to claim 7 , wherein the free magnetic element has an aspect ratio of 1.
11. A spin-transfer torque memory unit according to claim 7 , wherein the hard magnetic particles have a saturation moment of less than 500 emu/cm 3 .
12. A spin-transfer torque memory unit according to claim 7 , wherein the matrix of non-magnetic material is electrically insulating.
13. A spin-transfer torque memory unit according to claim 12 , further comprising an electrically conducting layer in electrical contact with the hard magnetic particles and the hard magnetic particles being in electrical contact with the soft magnetic layer.
14. A spin-transfer torque memory unit, comprising:
a free magnetic element comprising a hard magnetic layer exchanged coupled to a soft magnetic layer, the free magnetic element having a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit;
a reference magnetic element having a magnetization orientation that is pinned in a reference direction;
an electrically insulating and non-magnetic tunneling barrier layer separating the free magnetic element from the magnetic reference element; and
a magnetic compensation element adjacent to the free magnetic element, the magnetic compensation element applying a bias field on the magnetization orientation of the free magnetic element, wherein the bias field reduces a write current magnitude required to switch the direction of the magnetization orientation of the free magnetic element.
15. A spin-transfer torque memory unit according to claim 14 , further comprising a non-magnetic spacer layer separating the magnetic compensation element from the free magnetic element.
16. A spin-transfer torque memory unit according to claim 14 , wherein the soft magnetic layer has a spin polarization value greater than 0.5, and the hard magnetic layer has uniaxial magnetic anisotropy and a coercivity value greater than 1000 Oersteds.
17. A spin-transfer torque memory unit according to claim 14 , wherein the hard magnetic layer comprising a plurality of hard magnetic particles in a matrix of non-magnetic material.
18. A spin-transfer torque memory unit according to claim 17 , wherein the matrix of non\-magnetic material is electrically insulating.