Increased efficiency of current induced motion of chiral domain walls by interface engineering
The present invention relates to a magnetic domain wall displacement type memory cell (racetrack memory device) that includes a 4d or 5d metal dusting layer (DL) at the ferromagnetic/heavy metal interface of the ferromagnetic (FM) structure or the synthetic antiferromagnetic (SAF) structure of the basic racetrack device structure.
1 . A magnetic domain wall displacement type memory cell comprising a ferromagnetic layer, a heavy metal (HM) layer and a dusting layer (DL) consisting of a 4d metal, wherein the dusting layer is located at an interface between the ferromagnetic layer and the heavy metal layer of (i) a ferromagnetic (FM) structure or (ii) a synthetic antiferromagnetic (SAF) structure of a basic racetrack device structure,
wherein (i) the ferromagnetic (FM) structure comprises
one or more layer(s) of a ferromagnetic (FM) material
the heavy metal (HM) layer and
a coupling layer; and
(ii) the synthetic antiferromagnetic (SAF) structure comprises two layers of a ferromagnetic (FM) material which are coupled antiferromagnetically via a coupling layer, with the coupling layer disposed between the two ferromagnetic (FM) material layers to form a FM layer/coupling layer/FM layer sandwich, with said sandwich deposited on the dusting layer disposed on the heavy metal (HM) layer.
2 . The memory cell according to claim 1 , wherein the dusting layer has a thickness in the range of 0.1 to 1.5 nm.
3 . The memory cell according to claim 1 , wherein the dusting layer metal exhibits fcc structure.
4 . The memory cell according to claim 1 , wherein the dusting layer metal is Pd or Rh.
5 . The memory cell according to claim 4 , wherein the dusting layer metal is Pd.
6 . The memory cell according to claim 4 , wherein the HM layer is selected from at least one of Pt, Ir, W, Ta or Ru and has a thickness ranging from 0.8 to 2.0 nm.
7 . The memory cell according to claim 1 , wherein the ferromagnetic (FM) material is selected from the group consisting of:
Fe, Co, Ni or Mn,
an alloy of Fe and/or Co,
an alloy of Ni that may optionally further include one or more of Fe and Co,
an alloy of Mn that may optionally further include one or more of Fe, Co or Ni,
a compound including Fe and at least one of Ir, Al, Si or Ge, and
a compound including Mn and Si.
8 . The memory cell according to claim 1 , wherein the ferromagnetic (FM) structure comprises one or more layer(s) of the ferromagnetic material are sandwiched between the HM layer and the coupling layer.
9 . The memory cell according to claim 1 , wherein the HM layer includes at least one of Pt, Ir, W, Ta or Ru.
10 . The memory cell according to claim 1 , wherein the HM layer has a thickness of 0.8 nm to 2.0 nm.
11 . The memory cell according to claim 1 , wherein the coupling layer includes at least one of Ru, W, Ta or Ir.
12 . The memory cell according to claim 1 , wherein the coupling layer has a thickness of 0.4 nm to 1.5 nm.
13 . The memory cell according to claim 1 , wherein the ferromagnetic structure comprises more than one layer, and the two neighboring layers are identical or not identical.
14 . A method for reducing the threshold current densities and increasing the efficiency of domain wall motion in the magnetic domain wall displacement type memory cell according to claim 1 comprising introducing the 4d-metal dusting layer (DL) at the ferromagnetic/heavy metal (HM) interface of the ferromagnetic (FM) structure or the synthetic antiferromagnetic (SAF) structure of the racetrack memory device.
15 . A spintronics device comprising a memory cell according to claim 1 .
16 . The spintronics device according to claim 15 , wherein said spintronics device is selected from magnetic random access memories; magnetic recording hard disk drives; magnetic logic devices; security cards comprising magnetically stored information; semiconductor devices; or mesoscopic devices.
17 . The memory cell according to claim 1 , wherein the dusting layer has a thickness in the range of 0.1 to 1.0 nm.
18 . The memory cell according to claim 1 , wherein the dusting layer has a thickness in the range of 0.2 to 0.7 nm.
19 . The memory cell according to claim 1 , wherein the HM layer has a thickness of 1.0 nm to 1.8 nm.
20 . The memory cell according to claim 1 , wherein the HM layer has a thickness of 1.2 nm to 1.7.
21 . The memory cell according to claim 1 , wherein the coupling layer includes at least one of Ru or Ir.
22 . The memory cell according to claim 1 , wherein the coupling layer has a thickness of 0.6 nm to 1.0 nm.
23 . The memory cell according to claim 1 , wherein the coupling layer has a thickness of 0.7 nm to 0.9 nm.
24 . The memory cell according to claim 1 , wherein the ferromagnetic structure comprises more than one layer and two neighboring layers are not identical.
25 . The memory cell according to claim 1 , wherein the dusting layer has a spin-diffusion length of more than 5 nm.
26 . The memory cell according to claim 25 , wherein the dusting layer has a spin-diffusion length of greater than or equal to 55 Å and a Stoner criteria of greater than or equal to 0.57 to less than or equal to 1.0.
27 . The memory cell according to claim 26 , wherein the dusting layer has a Stoner criteria of greater than or equal to 0.85 to less than or equal to 1.0.
28 . The memory cell according to claim 1 , wherein the ferromagnetic (FM) material does not comprise Fe or an Fe alloy and the dusting layer consists of a 4d metal.
29 . A magnetic domain wall displacement type memory cell according to claim 1 , wherein the coupling layer comprises at least one of Ir, W, Ta or Ru and the ferromagnetic (FM) material does not include Fe or Fe alloy.
30 . A magnetic domain wall displacement type memory cell according to claim 1 having a remnant magnetization, M r , at a magnetization field of 0 T and a saturation magnetization, M s , at a magnetization field of 1.5 T and M r /M s has been tuned to zero.
31 . A magnetic domain wall displacement type memory cell comprising a ferromagnetic layer that does not include Fe or Fe alloy, a heavy metal (HM) layer and a dusting layer (DL) consisting of a 4d metal at the ferromagnetic layer/heavy metal layer interface of a ferromagnetic (FM) structure or a synthetic antiferromagnetic (SAF) structure, and a SAF structure with a 0.2 nm thick Pd or Rh dusting layer has a decrease of ~70% in threshold current density, J th in comparison to an otherwise identical structure with no dusting layer.