Co/Ni multilayers with improved out-of-plane anisotropy for magnetic device applications
View Patent ↗A MTJ for a domain wall motion device includes a thin seed layer that enhances perpendicular magnetic anisotropy (PMA) in an overlying laminated layer with a (Co/Ni) n composition or the like where n is from 2 to 30. The seed layer is preferably NiCr, NiFeCr, Hf, or a composite thereof with a thickness from 10 to 100 Angstroms. Furthermore, a magnetic layer such as CoFeB may be formed between the laminated layer and a tunnel barrier layer to serve as a transitional layer between a (111) laminate and (100) MgO tunnel barrier. There may be a Ta insertion layer between the CoFeB layer and laminated layer to promote (100) crystallization in the CoFeB layer. The laminated layer may be used as a reference layer, dipole layer, or free layer in a MTJ. Annealing between 300° C. and 400° C. may be used to further enhance PMA in the laminated layer.
1. A domain wall motion device, comprising:
(a) a first stack comprising a lower seed layer and a laminated layer formed thereon wherein the first stack has a first width and wherein the lower seed layer is one or more of Hf, NiCr, and NiFeCr, and the laminated layer has intrinsic PMA and a composition which includes two metals, a metal and alloy, or two alloys represented by (A1/A2) n or (A1/C/A2) where Al is a metal or alloy, A2 is a second metal or alloy, C is a non-magnetic spacer, and n is the number of laminates in the laminated layer; and
(b) a second stack with a tunnel barrier/free layer/capping layer configuration and having a second width substantially greater than the first width, the tunnel barrier contacts a top surface of the first stack.
2. The domain wall motion device of claim 1 wherein the lower seed layer consists of Hf, NiCr, NiFeCr, Hf/NiCr, Hf/NiFeCr, NiCr/Hf, or NiFeCr/Hf.
3. The domain wall motion device of claim 1 further comprised of a magnetic layer made of CoFeB, CoFe, or combinations thereof that is formed between the laminated layer and the tunnel barrier layer, the magnetic layer has PMA with a magnetization in the same direction as the PMA in the laminated layer.
4. The domain wall motion device of claim 1 wherein n is from 2 to 30, A1 is a first metal or alloy selected from one or more of Co, Ni, and Fe that may be doped with boron up to about 50 atomic %, A2 is a second metal or alloy selected from one or more of Co, Fe, Ni, Pt, and Pd, and A1 is unequal to A2.
5. The domain wall motion device of claim 1 wherein the free layer is part of a wire in an array of wires that is used to store digital information.
6. The domain wall motion device of claim 1 wherein the free layer has a plurality of domain walls that extend vertical from a bottom surface to a top surface of the free layer.
7. The domain wall motion device of claim 1 wherein the free layer has two ends that are connected to a current/voltage source in a first electrical loop to enable a write process.
8. The domain wall motion device of claim 7 wherein there is a second electrical loop that allows a readout of digital information in a switchable magnetic domain in the free layer during a read process.