Domain Wall Programmable Magnetic Logic
233
changed from dark to bright contrast, indicating a switch of the magnetization direction. This result clearly demonstrates that selective switching at either branch of the
network structure can be obtained by controlling the chirality of the transverse DW.
2.3 Chirality Dependant Vortex Domain Wall Selective
Switching
Similar investigations have been performed earlier by Pushp et al. [35] on VDW
motion at a bifurcation to understand the effect of chirality on the trajectory of the
DW. VDWs of opposite chirality moves along different branches giving rise to the
sorting effect similar to TDWs. Here, we discuss briefly the chirality dependant
VDW motion in magnetic branch structure. To ensure VDWs are stabilized, the
wire width was chosen to be 300 nm while the Ni 81 Fe 19 film thickness was 20 nm.
An alternative method of DW injection was used. By generating a local Oersted
field around a metallic strip placed orthogonal to the nanowire conduit, DW can
be nucleated on demand. To generate the DW with a particular chirality, a notch
was patterned beneath the strip line at the bottom edge of the nanowire. The notch
presets the magnetization rotation either in CW or ACW orientation depending on
the initial magnetization direction of the nanowire. For instance, when the nanowire
is saturated along −x-direction, the magnetic moments curl around the notch in
ACW fashion. When a voltage pulse is applied across the strip line, magnetization
reversal occurs in the region beneath the injection line. In this particular case, two
VDWs, HH and TT VDWs with ACW orientation are formed due to the influence
of the initial magnetization around the notch. However, when the strength of the
injection pulse is increased, it causes the oscillatory buckling of the magnetization
along the nanowire, alternating between the top and bottom edges with a periodicity
of 2 times the nanowire width. As the chirality of the VDW created at the bottom
edge is always ACW, the VDW created at the top edge is of CW orientation. Thus
by carefully controlling the strength of injection pulse one can generate a CW VDW
that is created at the top edge of the nanowire. In short, the strength of the injection
pulse can determine the chirality of the injected VDWs.
To demonstrate the chirality dependant VDW motion in branch structure, Yshaped nanostructure with each branch deviating 30° from the nanowire are patterned,
as shown in Fig. 7. When the HH VDW with an ACW chirality is injected and driven
with a magnetic field of 75 Oe, the VDW selectively moves towards the lower branch,
switching its magnetization, while the magnetization orientation of upper branch
remains unaffected as shown in Fig. 8a. In contrast, when a HH VDW with CW
chirality is injected (Fig. 8b), the DW selectively moves towards the upper branch. In
addition to the chirality, VDW is also characterized by its polarity of the core which
can be pointing in one of the two directions perpendicular plane of the nanowire
magnetization. The polarity of the vortex core does also affect the VDW motion at
the bifurcation. Certain combination of the vortex chirality and polarity needs less
233
changed from dark to bright contrast, indicating a switch of the magnetization direction. This result clearly demonstrates that selective switching at either branch of the
network structure can be obtained by controlling the chirality of the transverse DW.
2.3 Chirality Dependant Vortex Domain Wall Selective
Switching
Similar investigations have been performed earlier by Pushp et al. [35] on VDW
motion at a bifurcation to understand the effect of chirality on the trajectory of the
DW. VDWs of opposite chirality moves along different branches giving rise to the
sorting effect similar to TDWs. Here, we discuss briefly the chirality dependant
VDW motion in magnetic branch structure. To ensure VDWs are stabilized, the
wire width was chosen to be 300 nm while the Ni 81 Fe 19 film thickness was 20 nm.
An alternative method of DW injection was used. By generating a local Oersted
field around a metallic strip placed orthogonal to the nanowire conduit, DW can
be nucleated on demand. To generate the DW with a particular chirality, a notch
was patterned beneath the strip line at the bottom edge of the nanowire. The notch
presets the magnetization rotation either in CW or ACW orientation depending on
the initial magnetization direction of the nanowire. For instance, when the nanowire
is saturated along −x-direction, the magnetic moments curl around the notch in
ACW fashion. When a voltage pulse is applied across the strip line, magnetization
reversal occurs in the region beneath the injection line. In this particular case, two
VDWs, HH and TT VDWs with ACW orientation are formed due to the influence
of the initial magnetization around the notch. However, when the strength of the
injection pulse is increased, it causes the oscillatory buckling of the magnetization
along the nanowire, alternating between the top and bottom edges with a periodicity
of 2 times the nanowire width. As the chirality of the VDW created at the bottom
edge is always ACW, the VDW created at the top edge is of CW orientation. Thus
by carefully controlling the strength of injection pulse one can generate a CW VDW
that is created at the top edge of the nanowire. In short, the strength of the injection
pulse can determine the chirality of the injected VDWs.
To demonstrate the chirality dependant VDW motion in branch structure, Yshaped nanostructure with each branch deviating 30° from the nanowire are patterned,
as shown in Fig. 7. When the HH VDW with an ACW chirality is injected and driven
with a magnetic field of 75 Oe, the VDW selectively moves towards the lower branch,
switching its magnetization, while the magnetization orientation of upper branch
remains unaffected as shown in Fig. 8a. In contrast, when a HH VDW with CW
chirality is injected (Fig. 8b), the DW selectively moves towards the upper branch. In
addition to the chirality, VDW is also characterized by its polarity of the core which
can be pointing in one of the two directions perpendicular plane of the nanowire
magnetization. The polarity of the vortex core does also affect the VDW motion at
the bifurcation. Certain combination of the vortex chirality and polarity needs less