134
S. Krishnia and W. S. Lew
Fig. 29 The y-component of
the DW magnetization as a
function of current densities.
The side-view simulation
snapshots at low current
density (point ‘A’) and high
current density (point ‘B’)
are also shown
saturated at higher current density and the angle between the two DWs is fixed, which
results in the saturation of the exchange torque. The saturation of exchange torque
results in the saturation of DWs velocities at higher current densities. Therefore, the
SAF structures should be tuned in such a way that the upper and lower ferromagnetic
layers experience SHE in same direction to achieve the highest DW velocities. If the
magnetization rotation of the two DWs is opposite in directions, the perturbation in
antiferromagnetic coupling will be smaller compared to the previous case and that
will result in smaller DWs velocities. The higher perturbation in antiferromagnetic
alignment has been achieved by Krishnia et al., by placing Ta and Pt at opposite
interfaces of the SAF wires [89]. Based on the calculations, effects of capping and
seed layers on the DW dynamics in SAF wires are summarized in a Table 1.
As discussed in Sect. 3.2.2, the DMI stabilize the DWs into Néel configuration.
Figure 30a shows the DW velocity as a function of current density for two different
DMI values −0.5 mJ/m
2 (black) and −1.2 mJ/m
2 (red). A significant increment in
the DW velocity ~ 310 m/s is observed at a current density of 9 × 10
11 A/m
2 , when
the DMI is increased from −0.5 to −1.2 mJ/m
2 . Higher values of the DMI is shown
to increase the M x components of the DW which gives higher DW speeds due to
the spin Hall effect. Figure 30b shows the normalized x and y components of the
DW magnetization for two DMI values: −0.5 mJ/m
2 (solid lines) and −1.2 mJ/m
2
(dash lines). The increase in x-component with the higher DMI value indicates the
stabilization of the Néel DW. The results show that wires with high DMI values will
be helpful for the realization of high speed magnetic memory devices.
We have discussed the effects of various torques on DW dynamics in SAF wires.
The exchange torque plays a vital role in driving the DWs in SAF wires. Now we
explore how the DW dynamics is affected near magnetization compensation in such
devices. The net magnetization of the SAF layers can be tuned by varying upper
layer thickness. The hysteresis loops and the DWs velocities are shown in Fig. 31
for a series of SAF thin films, each with identical lower ferromagnetic layer but
upper ferromagnetic layer is varied. The DW velocities are found to increase with
S. Krishnia and W. S. Lew
Fig. 29 The y-component of
the DW magnetization as a
function of current densities.
The side-view simulation
snapshots at low current
density (point ‘A’) and high
current density (point ‘B’)
are also shown
saturated at higher current density and the angle between the two DWs is fixed, which
results in the saturation of the exchange torque. The saturation of exchange torque
results in the saturation of DWs velocities at higher current densities. Therefore, the
SAF structures should be tuned in such a way that the upper and lower ferromagnetic
layers experience SHE in same direction to achieve the highest DW velocities. If the
magnetization rotation of the two DWs is opposite in directions, the perturbation in
antiferromagnetic coupling will be smaller compared to the previous case and that
will result in smaller DWs velocities. The higher perturbation in antiferromagnetic
alignment has been achieved by Krishnia et al., by placing Ta and Pt at opposite
interfaces of the SAF wires [89]. Based on the calculations, effects of capping and
seed layers on the DW dynamics in SAF wires are summarized in a Table 1.
As discussed in Sect. 3.2.2, the DMI stabilize the DWs into Néel configuration.
Figure 30a shows the DW velocity as a function of current density for two different
DMI values −0.5 mJ/m
2 (black) and −1.2 mJ/m
2 (red). A significant increment in
the DW velocity ~ 310 m/s is observed at a current density of 9 × 10
11 A/m
2 , when
the DMI is increased from −0.5 to −1.2 mJ/m
2 . Higher values of the DMI is shown
to increase the M x components of the DW which gives higher DW speeds due to
the spin Hall effect. Figure 30b shows the normalized x and y components of the
DW magnetization for two DMI values: −0.5 mJ/m
2 (solid lines) and −1.2 mJ/m
2
(dash lines). The increase in x-component with the higher DMI value indicates the
stabilization of the Néel DW. The results show that wires with high DMI values will
be helpful for the realization of high speed magnetic memory devices.
We have discussed the effects of various torques on DW dynamics in SAF wires.
The exchange torque plays a vital role in driving the DWs in SAF wires. Now we
explore how the DW dynamics is affected near magnetization compensation in such
devices. The net magnetization of the SAF layers can be tuned by varying upper
layer thickness. The hysteresis loops and the DWs velocities are shown in Fig. 31
for a series of SAF thin films, each with identical lower ferromagnetic layer but
upper ferromagnetic layer is varied. The DW velocities are found to increase with