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. 2016 Jun 23:6:28590.
doi: 10.1038/srep28590.

Geometrically pinned magnetic domain wall for multi-bit per cell storage memory

M Al Bahri  1 , R Sbiaa  1
Affiliations

Geometrically pinned magnetic domain wall for multi-bit per cell storage memory

M Al Bahri et al. Sci Rep. .

Abstract

Spintronic devices currently rely on magnetic switching or controlled motion of domain walls (DWs) by an external magnetic field or a spin-polarized current. Controlling the position of DW is essential for defining the state/information in a magnetic memory. During the process of nanowire fabrication, creating an off-set of two parts of the device could help to pin DW at a precise position. Micromagnetic simulation conducted on in-plane magnetic anisotropy materials shows the effectiveness of the proposed design for pinning DW at the nanoconstriction region. The critical current for moving DW from one state to the other is strongly dependent on nanoconstricted region (width and length) and the magnetic properties of the material. The DW speed which is essential for fast writing of the data could reach values in the range of hundreds m/s. Furthermore, evidence of multi-bit per cell memory is demonstrated via a magnetic nanowire with more than one constriction.

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Figures

Figure 1
Figure 1
(a) Schematic representation of a stepped type nanowire where the step can be used for pinning domain wall. The dimensions of the nanowire and the step are shown in the figure. The magnetization is aligned in the film plane with easy axis along the x-axis. (b) An extended design to multi-bit per cell magnetic memory. (c) the critical current Jc to move domain wall from the pinning region as a function of the step depth d which is the off-set in the y-axis direction. The nanowire length L and width W were fixed to 200 nm and 40 nm, respectively and the magnetic properties of the investigated material are Ms = 600 kA/m and Ku = 1.0 × 105 J/m3.
Figure 2
Figure 2. Normalized x-component of nanowire magnetization as a function of time for different values of the step depth d.
The length and width of the nanowire were fixed to 200 nm and 40 nm, respectively. The magnetic properties of the investigated material are Ms = 600 kA/m and Ku = 0.5 × 105 J/m3 and J = 4.84 × 1012 A/m2.
Figure 3
Figure 3. Different positions for domain walls at different times for two values of d.
The length and width of the nanowire were fixed to 200 nm and 40 nm, respectively. The magnetic properties of the investigated material are Ms = 600 kA/m and Ku = 0.5 × 105 J/m3.
Figure 4
Figure 4
(a) Domain wall average velocity varies with current density for different values of magnetic anisotropy energy. The nanowire length L and width W were fixed to 200 nm and 40 nm, respectively and the saturation magnetization of the investigated material is Ms = 600 kA/m. (b) The relationship between critical current density and anisotropy energy.
Figure 5
Figure 5. Snapshot images of the nanowire with constriction for Ku = 0.5 × 105 J/m3 and 1.0 × 105 J/m3.
The length and width of the nanowire were fixed to 200 nm and 40 nm, respectively and the stepped region dimension d and l were both fixed to 20 nm. The calculation was carried at Ms = 600 kA/m and J = 5.5 × 1012 A/m2.
Figure 6
Figure 6. Normalized x-component of nanowire magnetization as a function of time for different values of Ms.
The device lateral dimensions are L = 200 nm, W = 40 nm, l = 20 nm and d = 20 nm. The material magnetic anisotropy is Ku = 0.5 × 105 J/m3 and J = 2.6 × 1012 A/m2.
Figure 7
Figure 7
(a) Phase diagram d–l for device with lateral dimension L = 200 nm and W = 40 nm. The material magnetic anisotropy are Ms = 600 kA/m and Ku = 0.5 × 105 J/m3. (b) Normalized x-component of nanowire magnetization as a function of time for selected values of d and l.
Figure 8
Figure 8
(a) The six states of nanowire of dimentions L = 200 nm, W = 40 nm, l = 10 nm and d = 30 nm. The magnetic properties of the investigated material are Ms = 600 kA/m and Ku = 0.5 × 105 J/m3. (b) Snapshot images of four states obtained at different current density values.
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