Templating layers for perpendicularly magnetized Heusler films
Devices are described that include a multi-layered structure that is non-magnetic at room temperature, and which comprises alternating layers of Co and at least one other element E (that is preferably Al; or Al alloyed with Ga, Ge, Sn or combinations thereof). The composition of this structure is represented by Co 1-x E x , with x being in the range from 0.45 to 0.55. The structure is in contact with a first magnetic layer that includes a Heusler compound. An MRAM element may be formed by overlying, in turn, the first magnetic layer with a tunnel barrier, and the tunnel barrier with a second magnetic layer (whose magnetic moment is switchable). Improved performance of the MRAM element may be obtained by placing an optional pinning layer between the first magnetic layer and the tunnel barrier.
1. A device, comprising:
a multi-layered structure that is non-magnetic at room temperature, the structure comprising alternating layers of Co and E, wherein E comprises at least one other element that includes Al, wherein the composition of the structure is represented by Co 1-x E x , with x being in the range from 0.45 to 0.55; and
a first magnetic layer that includes a Heusler compound, the magnetic layer being in contact with the structure.
2. The device of claim 1 , wherein the magnetic moment of the magnetic layer is substantially perpendicular to the interface between the structure and the magnetic layer.
3. The device of claim 2 , wherein the magnetic layer has a thickness of less than 5 nm.
4. The device of claim 2 , wherein the magnetic layer has a thickness of less than 3 nm.
5. The device of claim 2 , wherein the magnetic layer has a thickness of one unit cell.
6. The device of claim 1 , wherein the Heusler compound is selected from the group consisting of Mn 3.1-x Ge, Mn 3.1-x Sn, and Mn 3.1-x Sb, with x being in the range from 0 to 1.1.
7. The device of claim 1 , wherein the Heusler compound is a ternary Heusler.
8. The device of claim 7 , wherein the ternary Heusler is Mn 3.1-x Co 1.1-y Sn, wherein x≤1.2 and y≤1.0.
9. The device of claim 1 , wherein E is an AlGe alloy.
10. The device of claim 1 , wherein E is an AlGa alloy.
11. The device of claim 1 , wherein E includes an alloy selected from the group consisting of AlSn, AlGe, AlGaGe, AlGaSn, AlGeSn, and AlGaGeSn.
12. The device of claim 1 , comprising a substrate underlying the multi-layered structure.
13. The device of claim 12 , comprising a tunnel barrier overlying the first magnetic layer, thereby permitting current to pass through both the tunnel barrier and the first magnetic layer.
14. The device of claim 13 , comprising a second magnetic layer in contact with the tunnel barrier.
15. The device of claim 14 , wherein the tunnel barrier includes Mg and O.
16. A method, comprising:
using the device of claim 14 as a memory element.
17. The method of claim 16 , wherein the memory element is a racetrack memory device.
18. A method of forming the device of claim 1 , comprising:
depositing Co and Al, thereby forming a composite layer on a substrate;
annealing the composite layer, so that at least one layer of Co and at least one layer of Al are formed from the composite layer, thereby forming the multi-layered structure; and
depositing the magnetic layer over the multi-layered structure.
19. The method of claim 18 , wherein the annealing takes place at a temperature of at least 400° C.
20. The method of claim 18 , wherein the substrate is MgO.
21. A device, comprising:
a substrate;
a multi-layered structure that is non-magnetic at room temperature, the structure comprising alternating layers of Co and E, wherein E comprises at least one other element that includes Al, wherein the composition of the structure is represented by Co 1-x E x , with x being in the range from 0.45 to 0.55, wherein the structure overlies the substrate;
a first magnetic layer that includes a Heusler compound, the magnetic layer being in contact with the structure;
a tunnel barrier overlying the first magnetic layer; and
a second magnetic layer in contact with the tunnel barrier, wherein the second magnetic layer has a magnetic moment that is switchable.
22. The device of claim 21 , comprising a capping layer in contact with the second magnetic layer.
23. The device of claim 21 , wherein the first magnetic layer includes Mn and an element selected from the group consisting of Sn, Sb, and Ge.
24. The device of claim 23 , wherein the first magnetic layer further includes Co.
25. A device, comprising:
a multi-layered structure that is non-magnetic at room temperature, the structure comprising alternating layers of Co and E, wherein E comprises at least one other element that includes Al, wherein the composition of the structure is represented by Co 1-x E x , with x being in the range from 0.45 to 0.55; and
a first magnetic layer that includes an L1 0 compound, the magnetic layer being in contact with the structure.
26. The device of claim 25 , wherein the magnetic moment of the magnetic layer is substantially perpendicular to the interface between the structure and the magnetic layer.
27. The device of claim 25 , wherein the L1 0 compound is selected from the group consisting of MnGa, MnAl, FeAl, MnGe, MnSb, and MnSn alloys.
28. A method, comprising using the device of claim 25 as a memory element.
29. The method of claim 28 , wherein the memory element is a racetrack memory device.