Domain wall motion in perpendicularly magnetized wires having artificial antiferromagnetically coupled multilayers with engineered interfaces
Magnetic wires that include two antiferromagnetically coupled magnetic regions show improved domain wall motion properties, when the domain walls are driven by pulses of electrical current. The magnetic regions preferably include Co, Ni, and Pt and exhibit perpendicular magnetic anisotropy, thereby supporting the propagation of narrow domain walls. The direction of motion of the domain walls can be influenced by the order in which the wire's layers are arranged.
1. A method, comprising:
providing a magnetic wire that acts as a track for the motion of a domain wall, the wire including:
an underlayer;
a first magnetic region over, and in contact with, the underlayer and having an easy magnetization direction perpendicular to the interface between the underlayer and the first magnetic region, wherein the first magnetic region is ferromagnetic and/or ferrimagnetic;
a coupling layer over, and in contact with, the first magnetic region; and
a second magnetic region over, and in contact with, the coupling layer, wherein the second magnetic region is ferromagnetic and/or ferrimagnetic, and wherein the first magnetic region and the second magnetic region are antiferromagnetically coupled by the coupling layer; and
an overlayer over, and in contact with, the second magnetic region;
wherein (i) the underlayer, the first magnetic region, the coupling layer, the second magnetic region, and the overlayer extend along at least a portion of the length of the wire, and (ii) at least one of the underlayer and the overlayer includes a non-magnetic material (NMM) selected from the group of elements consisting of Pt, Pd, and Ir; and
applying current to the wire, thereby moving a domain wall along the wire, wherein the domain wall extends (i) across the first magnetic region, the coupling layer, and the second magnetic region and (ii) into at least a portion of the underlayer and/or a portion of the overlayer.
2. The method of claim 1 , wherein the first magnetic region includes a layer that is at least 20 atomic percent Co.
3. The method of claim 1 , wherein the second magnetic region includes a layer that is at least 20 atomic percent Co.
4. The method of claim 1 , wherein the first magnetic region includes a layer that is at least 20 atomic percent Ni.
5. The method of claim 1 , wherein the second magnetic region includes a layer that is at least 20 atomic percent Ni.
6. The method of claim 1 , wherein the first magnetic region and/or the second magnetic region includes both (i) a layer that is at least 20 atomic percent Co and (ii) a layer that is at least 20 atomic percent Ni.
7. The method of claim 1 , wherein the first magnetic region, the second magnetic region, and the layer that includes the non-magnetic material are all fcc and (111) oriented.
8. The method of claim 1 , wherein the first magnetic region and/or the second magnetic region includes at least one trilayer selected from the group consisting of Co/Pt/Ni and Ni/Pt/Co, wherein (i) each Ni layer in said at least one trilayer is ferromagnetic and includes at least 20 atomic percent Ni, (ii) each Co layer in said at least one trilayer is ferromagnetic and includes at least 20 atomic percent Co, and (iii) each Pt layer in said at least one trilayer includes at least 70 atomic percent Pt.
9. The method of claim 8 , wherein each Ni layer in said at least one trilayer is fcc and (111) oriented.
10. The method of claim 8 , wherein each Ni layer in said at least one trilayer has a thickness between 1 and 10 angstroms.
11. The method of claim 8 , wherein each Ni layer in said at least one trilayer has a thickness between 4 and 8 angstroms.
12. The method of claim 1 , wherein the first and/or second magnetic region includes at least one Co/Ni/Co trilayer, in which each Co layer in said at least one trilayer is at least 20 atomic percent Co, and each Ni layer in said at least one trilayer is at least 20 atomic percent Ni.
13. The method of claim 1 , wherein the first and/or second magnetic region includes at least one Co/Ni/Pt/Co multi-layer, in which each Co layer in said at least one multi-layer is at least 20 atomic percent Co, each Ni layer in said at least one multi-layer is at least 20 atomic percent Ni, and each Pt layer in said at least one multi-layer is at least 70 atomic percent Pt.
14. The method of claim 1 , wherein each of the first and second magnetic regions includes at least one trilayer selected from the group consisting of Co/Pt/Ni and Ni/Pt/Co, wherein (i) each Ni layer in said at least one trilayer is ferromagnetic and includes at least 20 atomic percent Ni, (ii) each Co layer in said at least one trilayer is ferromagnetic and includes at least 20 atomic percent Co, and (iii) each Pt layer in said at least one trilayer includes at least 70 atomic percent Pt.
15. The method of claim 1 , wherein the coupling layer includes Ru and is in contact with (i) a Pt layer in the first magnetic region and/or (ii) a Pt layer in the second magnetic region.
16. The method of claim 1 , wherein the coupling layer includes at least one of Ru and Os.
17. The method of claim 16 , wherein Ru and Os together constitute at least 99 atomic percent of the coupling layer.
18. The method of claim 1 , wherein the coupling layer includes Ru and is between 4 and 10 angstroms thick.
19. The method of claim 1 , wherein the coupling layer includes Os and is between 4 and 10 angstroms thick.
20. The method of claim 1 , wherein the coupling layer includes Ru and is contact with (i) a Co layer in the first magnetic region and (ii) a Co layer in the second magnetic region.
21. The method of claim 1 , wherein each Co layer in the wire is fcc and (111) oriented.
22. The method of claim 1 , wherein each Co layer in the wire has a thickness between 1 and 10 angstroms.
23. The method of claim 1 , wherein each Co layer in the wire has a thickness between 1 and 4.5 angstroms.
24. The method of claim 1 , wherein the underlayer or the overlayer that includes a NMM has a thickness between 2 and 50 angstroms.
25. The method of claim 1 , wherein the underlayer or the overlayer that includes a NMM has a thickness between 5 and 15 angstroms.
26. The method of claim 1 , wherein the underlayer or the overlayer has a magnetic moment that is induced by its proximity to a Co layer.
27. The method of claim 26 , wherein a portion of the induced moment is parallel to the interface.
28. The method of claim 26 , wherein a portion of the induced moment is perpendicular to the orientation of the Co moment in the proximal Co layer.
29. The method of claim 1 , comprising applying current to the wire, thereby moving a plurality of domain walls along the wire.
30. The method of claim 1 , wherein the domain wall moves in the direction of the applied current, the number of NMM/Co interfaces in at least one of the first and second regions being greater than the number of Co/NMM interfaces in said at least one of the regions.
31. The method of claim 1 , wherein the domain wall moves in the direction opposite to that of the applied current, the number of Co/NMM interfaces in at least one of the first and second regions being greater than the number of NMM/Co interfaces in said at least one of the regions.
32. A method, comprising:
providing a magnetic wire that acts as a track for the motion of a domain wall, the wire including:
a first magnetic region that is ferromagnetic and/or ferrimagnetic;
a coupling layer over, and in contact with, the first magnetic region, the first magnetic region having an easy magnetization direction perpendicular to the interface between the first magnetic region and the coupling layer; and
a second magnetic region over, and in contact with, the coupling layer, wherein the second magnetic region is ferromagnetic and/or ferrimagnetic, and wherein the first magnetic region and the second magnetic region are antiferromagnetically coupled by the coupling layer, so that the absolute value of the wire's remanent magnetization is less than 0.50 times the sum of (i) the absolute value of the magnitude of the first magnetic region's magnetization and (ii) the absolute value of the magnitude of the second magnetic region's magnetization; and
wherein the first magnetic region, the coupling layer, and the second magnetic region extend along at least a portion of the length of the wire; and
applying current to the wire, thereby moving a domain wall along the wire, wherein the domain wall extends across the first magnetic region, the coupling layer, and the second magnetic region.
33. The method of claim 32 , wherein the absolute value of the wire's remanent magnetization is less than 0.25 times the sum.
34. The method of claim 32 , wherein the wherein the absolute value of the wire's remanent magnetization is less than 0.10 times the sum.
35. The method of claim 32 , wherein:
the wire includes an underlayer that includes an element selected from the group consisting of Pt, Pd, and Ir, the first magnetic region being over, and in contact with, the underlayer; and
the domain wall extends into at least a portion of the underlayer.
36. The method of claim 32 , wherein:
the wire includes an overlayer that includes an element selected from the group consisting of Pt, Pd, and Ir, the overlayer being over, and in contact with, the second magnetic region; and
the domain wall extends into at least a portion of the overlayer.
37. The method of claim 32 , wherein the first magnetic region and/or the second magnetic region includes both (i) a layer that is at least 20 atomic percent Co and (ii) a layer that is at least 20 atomic percent Ni.
38. The method of claim 32 , wherein the first magnetic region and the second magnetic region are both fcc and (111) oriented.
39. The method of claim 32 , wherein the first magnetic region and/or the second magnetic region includes at least one trilayer selected from the group consisting of Co/Pt/Ni and Ni/Pt/Co, wherein (i) each Ni layer in said at least one trilayer is ferromagnetic and includes at least 20 atomic percent Ni, (ii) each Co layer in said at least one trilayer is ferromagnetic and includes at least 20 atomic percent Co, and (iii) each Pt layer in said at least one trilayer includes at least 70 atomic percent Pt.
40. The method of claim 32 , wherein the coupling layer includes Ru and is in contact with (i) a Pt layer in the first magnetic region and/or (ii) a Pt layer in the second magnetic region.
41. The method of claim 32 , wherein the coupling layer includes at least one of Ru and Os.
42. The method of claim 32 , comprising applying current to the wire, thereby moving a plurality of domain walls along the wire.
43. The method of claim 32 , wherein the domain wall moves in the direction of the applied current, the number of non-magnetic material (NMM)/Co interfaces in at least one of the first and second regions being greater than the number of Co/NMM interfaces in said at least one of the regions.
44. The method of claim 32 , wherein the domain wall moves in the direction opposite to that of the applied current, the number of Co/NMM (non-magnetic material) interfaces in at least one of the first and second regions being greater than the number of NMM/Co interfaces in said at least one of the regions.