Read Back Signals in Magnetic Recording - Research Group Fidler

FEM Simulations
5.1.4, are used in modern spin valves.) The transfer curve and the slope at zero point do not
differ much compared to the low exchange bias field. However, for large fields we have a
much better sensor performance in respect to sensitivity and symmetry. The higher voltage in
equilibrium is due to the larger angle between both magnetizations. The large exchange bias
field reduces the deflection due to the hard bias, while the free layer magnetization stays
unmodified, because of the widely unchanged demagnetizing field of the pinned layer.
6.2.3 Influence of Shields
Now the shields are taken into account. It is expected that the shields have an influence on the
transfer curve due to the mirror currents (see Section 5.1.5). Indeed the shields have a large
influence. Again the transfer curve is evaluated by applying the external field shown in Figure
6.5 on the GMR element. The shields are not exposed to the external field. The result is given
in Figure 6.7.
Output Voltage [V]
0.109
0.108
0.107
0.106
0.105
0.104
0.103
0.102
-0.10 -0.05 0.00 0.05 0.10
H z [T]
ΔR/R [%]
without shields
with shields
-0.10 -0.05 0.00 0.05 0.10
H z [T]
Figure 6.7: The transfer curves for the spin valve with and without shields (for both
Hexch = 0.1 T).
The presence of shields generally leads to a greater output voltage, particularly at zero field.
The origin of this effect is based on mirror currents. They reduce the current field which
works against the demagnetizing field of the pinned layer. Therefore the demagnetizing field
2
1
0
-1
-2
-3
-4
-5
72