Magnetic memory devices

1. A magnetic memory device comprising a magnetic tunnel junction, wherein the magnetic tunnel junction comprises:

a fixed layer;

a polarization enhancement structure on the fixed layer;

a tunnel barrier layer on the polarization enhancement structure; and

a free layer on the tunnel barrier layer,

wherein the polarization enhancement structure comprises a plurality of polarization enhancement layers and at least one spacer layer which separates the plurality of polarization enhancement layers from each other, with a first and second of the plurality of polarization enhancement layers both directly contacting a spacer layer of the at least one spacer layer therebetween,

wherein each of the plurality of polarization enhancement layers comprises a ferromagnetic material and each of at least one spacer layers comprises a ferromagnetic material and a non-magnetic material,

wherein a thickness of each of the plurality of polarization enhancement layers is from about 5 Å to about 20 Å, and

wherein a thickness of the at least one spacer layer is from about 2 Å to about 15 Å.

2. The magnetic memory device of claim 1 , wherein a thickness of the polarization enhancement structure is from about 12 Å to about 140 Å.

3. The magnetic memory device of claim 1 , wherein a number of polarization enhancement layers is between two and ten, inclusive, and

wherein a number of the at least one spacer layer is between one and ten, inclusive.

4. The magnetic memory device of claim 1 , wherein each of the at least one spacer layer comprises the non-magnetic material in an amount equal to or greater than about 50 at % and less than about 100 at %.

5. The magnetic memory device of claim 1 , wherein the ferromagnetic material of the polarization enhancement layers comprises at least one first element from among cobalt (Co), iron (Fe), nickel (Ni), and at least one second element from among boron (B), silicon (Si), zirconium (Zr), hafnium (Hf), beryllium (Be), aluminum (Al), carbon (C), tantalum (Ta), and copper (Cu).

6. The magnetic memory device of claim 1 , wherein each of the at least one spacer layer comprises the non-magnetic material as grains and the ferromagnetic material as a grain boundary of the grains.

7. The magnetic memory device of claim 1 , wherein the non-magnetic material comprises tungsten (W), molybdenum (Mo), platinum (Pt), iridium (Ir), hafnium (Hf), chromium (Cr), ruthenium (Ru), niobium (Nb), zirconium (Zr), vanadium (V), palladium (Pd), oxygen (O), nitride (N), or combinations thereof.

8. The magnetic memory device of claim 7 , wherein the non-magnetic material comprises Mo.

9. The magnetic memory device of claim 1 , wherein each of the at least one spacer layer comprises the ferromagnetic material as nano particles.

10. The magnetic memory device of claim 1 , wherein the ferromagnetic material of the at least one spacer layer comprises cobalt (Co), iron (Fe), nickel (Ni), gadolinium (Gd), samarium (Sm), neodymium (Nd), praseodymium (Pr), or combinations thereof.

11. The magnetic memory device of claim 1 , further comprising a perpendicular magnetic anisotropy enhancement layer on the free layer.

12. The magnetic memory device of claim 11 , further comprising a capping layer on the perpendicular magnetic anisotropy enhancement layer.

13. The magnetic memory device of claim 1 , wherein the fixed layer comprises a first fixed layer, a second fixed layer, and an anti-parallel coupling layer between the first fixed layer and the second fixed layer.

14. A magnetic memory device comprising a magnetic tunnel junction, wherein the magnetic tunnel junction comprises:

a fixed layer;

a polarization enhancement structure on the fixed layer;

a tunnel barrier layer on the polarization enhancement structure; and

a free layer on the tunnel barrier layer,

wherein the polarization enhancement structure comprises a plurality of cobalt-iron-boron (CoFeB) layers and at least one molybdenum-cobalt-iron (MoCoFe) layer which separates the plurality of CoFeB layers from each other.

15. The magnetic memory device of claim 14 , wherein each of the at least one MoCoFe layers comprises Mo in an amount equal to or greater than about 50 at % and less than about 100 at %.

16. The magnetic memory device of claim 14 , wherein a thickness of each of the plurality of CoFeB layers is from about 5 Å to about 20 Å.

17. The magnetic memory device of claim 14 , wherein a thickness of each of the at least one MoCoFe layers is from about 2 Å to about 15 Å.

18. A magnetic memory device comprising a magnetic tunnel junction, wherein the magnetic tunnel junction comprises:

a fixed layer;

a polarization enhancement structure on the fixed layer;

a tunnel barrier layer on the polarization enhancement structure; and

a free layer on the tunnel barrier layer,

wherein the polarization enhancement structure comprises a plurality of polarization enhancement layers alternately stacked with a plurality of spacer layers, the plurality of polarization enhancement layers comprising a first polarization layer and a second polarization layer, the first polarization layer and the second polarization layer both directly contacting a first spacer layer of the plurality of spacer layers therebetween,

wherein the first and second polarization layers comprise a ferromagnetic material and the first spacer layer comprises both a ferromagnetic material and a non-magnetic material, and

wherein a thickness of the first of the plurality of polarization enhancement layers is different from a thickness of the second of the plurality of polarization enhancement layers.

19. The magnetic memory device of claim 18 , wherein the plurality of polarization enhancement layers comprises a first polarization enhancement layer and a second polarization enhancement layer,

wherein the second polarization enhancement layer is closer to the tunnel barrier layer than the first polarization enhancement layer is to the tunnel barrier layer, and

wherein a thickness of the second polarization enhancement layer is greater than a thickness of the first polarization enhancement layer.

20. The magnetic memory device of claim 18 , wherein a thickness of one of the plurality of spacer layers is different from a thickness of another one of the plurality of spacer layers.