Free layer with out-of-plane anisotropy for magnetic device applications
View Patent ↗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.
1. A magnetic device having thermal stability to at least 400° C., comprising:
(a) a synthetic antiferromagnetic (SAF) free layer that has a FL1/DL1/first coupling layer/DL2/FL2 configuration wherein FL1 and FL2 are free layers exhibiting perpendicular magnetic anisotropy, the first 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 between FL1 and FL2;
(b) a synthetic antiferromagnetic (SAF) reference layer that has a RL1/DL5/second coupling layer/DL6/RL2 configuration wherein RL1 and RL2 are reference layers exhibiting perpendicular magnetic anisotropy, the second coupling layer is a non-magnetic metal that induces RKKY (antiferromagnetic) coupling between the RL1 and RL2 layers, and DL5 and DL6 are Co, Fe, Ni, CoNiFe, or NiFe dusting layers that enhance the RKKY coupling between RL1 and RL2; 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.
2. The magnetic device of claim 1 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 RL2 layer contacts a bottom surface of the non-magnetic spacer.
3. The magnetic device of claim 1 wherein one or more of the FL1, FL2, RL1, and RL2 layers are made of a laminate that is (Ni/Co) n , (Pd/Co) n , (Pt/Co) n , (Co/RO 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.
4. The magnetic device of claim 1 wherein one or more of the FL1, FL2, RL1, and RL2 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.
5. The magnetic device of claim 1 wherein one or more of the FL1, FL2, RL1, and RL2 layers are CoFeB or CoNiFeB.
6. The magnetic device of claim 1 wherein the first and second coupling layers are one of Ru, Rh, Ir, Cu, Cr, or Mo.
7. The magnetic device of claim 6 wherein each of the first and second coupling layers has a thickness of about 4, 9, or 13 Angstroms.
8. The magnetic device of claim 1 wherein each of the DL1, DL2, DL5, and DL6 dusting layers has a thickness from about 1 to 10 Angstroms.