Magnetic tunnel junction and magnetic memory device comprising the same
In one embodiment, the magnetic memory device includes a free layer structure having a variable magnetization direction. The free layer structure includes a first free layer, the first free layer being a first Heusler alloy; a coupling layer on the first free layer, the coupling layer including a metal oxide layer; and a second free layer on the metal oxide layer, the second free layer being a second Heusler alloy, the second Heusler alloy being different from the first Heusler alloy.
1. A magnetic memory device, comprising:
a free layer structure having a variable magnetization direction, the free layer structure including,
a first free layer, the first free layer including a first Heusler alloy having perpendicular magnetic anisotropy,
a coupling layer on the first free layer, the coupling layer including a metal oxide layer, and
a second free layer on the metal oxide layer, the second free layer including a second Heusler alloy comprising a material different from the first Heusler alloy and having perpendicular magnetic anisotropy;
a pinned layer structure, the pinned layer structure having a fixed magnetization direction; and
a tunnel barrier layer between the pinned layer structure and the free layer structure,
wherein the metal oxide layer including at least one of magnesium aluminum oxide (MgAlO), hafnium oxide (HfO), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), zirconium oxide (ZrO), and aluminum oxide (AlO),
wherein the metal oxide layer induces interfacial perpendicular magnetic anisotropy at an interface with the first free layer.
2. The magnetic memory device of claim 1 , wherein the first Heusler alloy having a first perpendicular magnetic anisotropy energy and the second Heusler alloy having a second perpendicular magnetic anisotropy energy greater than the first perpendicular magnetic anisotropy energy.
3. The magnetic memory device of claim 2 , wherein the first free layer is interposed between the second free layer and the tunnel barrier layer.
4. The magnetic memory device of claim 1 , wherein a magnetic coupling strength between the first free layer and the second free layer is 0.05-1 erg/cm 2 .
5. The magnetic memory device of claim 1 , wherein a thickness of the metal oxide layer is less than or equal to 1.5 nm.
6. The magnetic memory device of claim 1 , wherein the first Heusler alloy has a first saturation magnetization, and
the second Heusler alloy has a second saturation magnetization being less than the first saturation magnetization.
7. The magnetic memory device of claim 1 , wherein the first free layer, the coupling layer and the second free layer form an exchange coupled composite (ECC).
8. The magnetic memory device of claim 1 , wherein the first free layer has a cubic structure.
9. The magnetic memory device of claim 1 , wherein the first free layer has a saturation magnetization of 1200 emu/cc or less.
10. The magnetic memory device of claim 1 , wherein the first free layer has a saturation magnetization of 500-1200 emu/cc.
11. The magnetic memory device of claim 1 , wherein the first free layer has a tunneling magnetoresistance ratio at room temperature of greater than 100%.
12. The magnetic memory device of claim 1 , wherein the first free layer has thickness of 5 nm or less.
13. The magnetic memory device of claim 1 , wherein the second free layer has a tetragonal structure.
14. The magnetic memory device of claim 1 , wherein the second free layer has a saturation magnetization of less than or equal to 500 emu/cc.
15. The magnetic memory device of claim 1 , wherein the second free layer has a thickness of 10 nm or less.
16. A magnetic memory device, comprising:
a pinned layer structure, the pinned layer structure having a fixed magnetization direction, the pinned layer structure including,
a first pinned layer,
a non-magnetic layer, and
a second pinned layer, the first pinned layer and the second pinned layer having anti-parallel magnetization directions;
a free layer structure having a variable magnetization direction, the free layer structure including,
a first free layer, the first free layer including a first Heusler alloy, and having a first saturation magnetization,
a metal oxide layer on the first free layer, and
a second free layer on the metal oxide layer, the second free layer including a second Heusler alloy having a second saturation magnetization, and the second saturation magnetization being different from the first saturation magnetization; and
a tunnel barrier layer between the pinned layer structure and the free layer structure,
wherein the metal oxide layer includes at least one of magnesium aluminum oxide (MgAlO), hafnium oxide (HfO), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), zirconium oxide (ZrO), and aluminum oxide (AlO), and
wherein the metal oxide layer induces interfacial perpendicular magnetic anisotropy at an interface with the first free layer.
17. The magnetic memory device of claim 16 , wherein the first free layer has a cubic structure.
18. The magnetic memory device of claim 16 , wherein the second free layer has a tetragonal structure.
19. The magnetic memory device of claim 16 , wherein a magnetic coupling strength between the first free layer and the second free layer is 0.05-1 erg/cm 2 .