Free layer with out-of-plane anisotropy for magnetic device applications

Patent metadata

Field	Value
Publication number	US-9252710-B2
Application number	US-201213686169-A
Country	US
Kind code	B2
Filing date	Nov 27, 2012
Priority date	Nov 27, 2012
Publication date	Feb 2, 2016
Grant date	Feb 2, 2016

Abstract

Synthetic antiferromagnetic (SAF) and synthetic ferrimagnetic (SyF) free layer structures are disclosed that reduce Ho (for a SAF free layer), increase perpendicular magnetic anisotropy (PMA), and provide higher thermal stability up to at least 400° C. The SAF and SyF structures have a FL1/DL1/spacer/DL2/FL2 configuration wherein FL1 and FL2 are free layers with PMA, the coupling layer induces antiferromagnetic or ferrimagnetic coupling between FL1 and FL2 depending on thickness, and DL1 and DL2 are dusting layers that enhance the coupling between FL1 and FL2. The SAF free layer may be used with a SAF reference layer in STT-MRAM memory elements or in spintronic devices including a spin transfer oscillator. Furthermore, a dual SAF structure is described that may provide further advantages in terms of Ho, PMA, and thermal stability.

First claim

We claim:

1. A synthetic antiferromagnetic (SAF) free layer stack having a thermal stability to at least 400° C. in a magnetic device, comprising:
(a) a first free layer (FL1) and a second free layer (FL2) each exhibiting perpendicular magnetic anisotropy;
(b) a coupling layer that induces RKKY (antiferromagnetic) coupling between the FL1 and FL2 layers; and
(c) a first dusting layer (DL1) and a second dusting layer (DL2) made of Fe, Ni, NiFe, or CoFeNi that enhance the RKKY coupling between the FL1 and FL2 layers, the SAF free layer stack has a structure in which FL1, DL1, coupling layer, DL2, and FL2 layers are consecutively deposited on a substrate that is a tunnel barrier layer or a Cu spacer to give a substrate/FL1/DL1/coupling layer/DL2/FL2 configuration.

2. The SAF free layer stack of claim 1 wherein one or both of the FL1 and FL2 layers are made of a laminate that is (Ni/Co) n , (Pd/Co) n , (Pt/Co) n , (Co/Ru) n , (Ni/CoFe) n , (Ni/CoFeB) n , (NiFe/Co) n , (NiFeB/Co) n , or (NiCo/Co) n where n is the number of laminations and n is between about 1 and 10.

3. The SAF free layer stack of claim 1 wherein the coupling layer is Ru, Rh, Ir, Cu, Cr, or Mo and has a thickness of about 4, 9, or 13 Angstroms.

4. The SAF free layer stack of claim 1 wherein one or both of the FL1 and FL2 layers are a L1 0 alloy that is FePt, CoPt, FePd, NiPt, FeNi, FeCu, MnAl, MnPt, MnPd, or CuAu, or are made of a rare earth-transition metal (RE-TM) alloy.

5. The SAF free layer stack of claim 1 wherein one or both of the FL1 and FL2 layers are comprised of CoFeB or CoNiFeB.

6. The SAF free layer stack of claim 1 wherein the DL1 and DL2 dusting layers have a thickness of about 1 to 50 Angstroms.

7. The SAF free layer stack of claim 1 wherein the substrate is a stack of layers with a bottom seed layer, reference layer, and an upper non-magnetic spacer, the FL1 layer contacts a top surface of the non-magnetic spacer.

8. The SAF free layer stack of claim 1 wherein a capping layer contacts a top surface of the FL2 layer, the capping layer is made of one or more non-magnetic metals or is a dielectric layer.

9. A magnetic device having thermal stability to at least 400° C., comprising:
(a) a synthetic antiferromagnetic (SAF) free layer that has a FL1/DL1/coupling layer/DL2/FL2 configuration wherein FL1 and FL2 are free layers exhibiting perpendicular magnetic anisotropy, the coupling layer is a non-magnetic metal that induces RKKY (antiferromagnetic) coupling between the FL1 and FL2 layers, and DL1 and DL2 are Co, Fe, Ni, CoNiFe, or NiFe dusting layers that enhance the RKKY coupling;
(b) a synthetic antiferromagnetic (SAF) reference layer; and
(c) a non-magnetic spacer formed between the SAF reference layer and SAF free layer wherein the FL1 layer contacts a top surface of the non-magnetic spacer that is a tunnel barrier layer or a Cu spacer in a bottom spin valve configuration, or the FL2 layer contacts a bottom surface of the non-magnetic spacer in a top spin valve configuration.

10. The magnetic device of claim 9 that has a bottom spin valve configuration wherein the SAF reference layer, a transition layer made of CoNiFeB, CoFe, CoFeB, Co, or composites thereof, the non-magnetic spacer, and the SAF free layer are sequentially formed on a substrate that is a seed layer.

11. The magnetic device of claim 9 that has a bottom spin valve configuration wherein the SAF reference layer, non-magnetic spacer, and SAF free layer are sequentially formed on a substrate that is a seed layer, and the SAF reference layer has a AP2/second coupling layer/AP1 configuration wherein the AP1 layer exhibits PMA and contacts a bottom surface of the non-magnetic spacer.

12. The magnetic device of claim 11 wherein the AP2 layer has PMA, the second coupling layer enables RKKY coupling between AP2 and AP1 layers, and the SAF reference layer is further comprised of a dusting layer between the AP2 layer and second coupling layer, and a dusting layer between the second coupling layer and the AP1 layer to enhance RKKY coupling between the AP1 and AP2 layers.

13. The magnetic device of claim 9 wherein one or both of the FL1 and FL2 layers are made of a laminate that is (Ni/Co) n , (Pd/Co) n , (Pt/Co) n , (Co/Ru) n , (Ni/CoFe) n , (Ni/CoFeB) n , (NiFe/Co) n , (NiFeB/Co) n , or (NiCo/Co) n where n is the number of laminations and n is between about 1 and 10.

14. The magnetic device of claim 9 wherein one or both of the FL1 and FL2 layers are a L1 0 alloy that is FePt, CoPt, FePd, NiPt, FeNi, FeCu, MnAl, MnPt, MnPd, or CuAu, or are a rare earth-transition metal (RE-TM) alloy.

15. The magnetic device of claim 9 wherein one or both of the FL1 and FL2 layers are CoFeB or CoNiFeB.

16. The magnetic device of claim 9 wherein the coupling layer is Ru, Rh, Ir, Cu, Cr, or Mo and has a thickness of about 4, 9, or 13 Angstroms.

17. The magnetic device of claim 9 wherein the DL1 and DL2 dusting layers have a thickness from about 1 to 10 Angstroms.

18. A spin transfer oscillator (STO) structure, comprising:
(a) a first non-magnetic layer (NM1) which adjoins a substrate that is a first terminal;
(b) a spin injection layer (SIL) that is a synthetic antiferromagnetic (SAF) reference layer, the SIL contacts the first non-magnetic layer;
(c) a second non-magnetic layer (NM2) that adjoins a second terminal;
(d) a field generation layer (FGL) that contacts the second non-magnetic layer and has a FL1/DL1/coupling layer/DL2/FL2 configuration wherein FL1 and FL2 are free layers exhibiting perpendicular magnetic anisotropy, the coupling layer is a non-magnetic metal that induces RKKY (antiferromagnetic) coupling between the FL1 and FL2 layers, and DL1 and DL2 are Co, Fe, Ni, CoNiFe, or NiFe dusting layers that enhance the RKKY coupling; and
(e) a third non-magnetic layer (NM3) formed between the spin injection layer and the field generation layer to give a STO stack with a NM1/SIL/NM3/FGL/NM2 configuration.

19. The STO structure of claim 18 wherein the first terminal is a main pole layer and the second terminal is a write shield in a microwave assisted magnetic recording device.

20. The STO structure of claim 18 wherein one or both of the FL1 and FL2 layers are made of a laminate that is (Ni/Co) n , (Pd/Co) n , (Pt/Co) n , (Co/Ru) n , (Ni/CoFe) n , (Ni/CoFeB) n , (NiFe/Co) n , (NiFeB/Co) n , or (NiCo/Co) n where n is the number of laminations and n is between about 1 and 10.

21. The STO structure of claim 18 wherein one or both of the FL1 and FL2 layers are a L1 0 alloy that is FePt, CoPt, FePd, NiPt, FeNi, FeCu, MnAl, MnPt, MnPd, or CuAu, or are a rare earth-transition metal (RE-TM) alloy.

22. The STO structure of claim 18 wherein one or both of the FL1 and FL2 layers are CoFeB or CoNiFeB.

23. The STO structure of claim 18 wherein the coupling layer is Ru, Rh, Ir, Cu, Cr, or Mo and has a thickness of about 4, 9, or 13 Angstroms.

24. The STO structure of claim 18 wherein the DL1 and DL2 dusting layers have a thickness from about 1 to 10 Angstroms.

25. A dual synthetic antiferromagnetic (SAF) free layer stack, comprising:
(a) a first free layer (FL1) and a second free layer (FL2) each exhibiting perpendicular magnetic anisotropy;
(b) a first spacer that induces RKKY (antiferromagnetic) coupling between the FL1 and FL2 layers;
(c) a first dusting layer (DL1) and a second dusting layer (DL2) that enhance the RKKY coupling between the FL1 and FL2 layers;
(d) a third free lay

Assignees

• Headway Technologies Inc

Inventors

• Wang Yu-Jen
• Jan Guenole
• Tong Ru-Ying

Classifications

• G11B5/65

  characterised by its composition (G11B5/66 takes precedence) · CPC title

• G01R33/00

  Arrangements or instruments for measuring magnetic variables · CPC title

• G11B2005/0024

  Microwave assisted recording · CPC title

• H03B15/006 Primary

  using spin transfer effects or giant magnetoresistance · CPC title

• H01F10/3286

  Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy · CPC title