Read Back Signals in Magnetic Recording - Research Group Fidler

Read Head Design
Figure 5.2: A comparison (left) of a conventional spin valve and a spin valve using a
synthetic ferromagnet to fix the pinned layer [20]. The interlayer exchange constant (right)
for two Ni80Co20 layers as function of the Ru spacer layer thickness [32].
The IEC effect has its origin in quantum interference of electron states [36]. The exchange
coupling constant J IEC [J/m 2 ] depends on the nonmagnetic layer thickness t NM like
⎛ tNM
⎞
sin ⎜2π +Φ
Λ
⎟
J = J
⎝ ⎠
(5.4)
IEC
0 2
tNM
as shown in Figure 5.2. Λ , Φ , and J 0 are constants, depending on the composition of the
layers. The advantage of spin-valves with a synthetic antiferromagnetic pinned layer is the
very large exchange field of IEC up to 0.5 T. This is an increase of a factor 10 compared to
the direct exchange coupling with an antiferromagnet. So the stability against external fields
is much better due to the higher anisotropy. Moreover the demagnetizing fields of the two
ferromagnetic layers Fp,1 and Fp,2 cancel each other partially, which leads to a reduced
influence on the free layer.
5.1.5 Sense Current
The sense current flowing through the GMR sensor generates a magnetic field. This field also
influences the pinned layer magnetization. For conventional simple spin valves there is one
current direction which is more favorable. The main part of the current flows through the Cu
layer, due to its higher conductivity compared to the other layers. So the current field either
adds up with the demagnetizing field of the pinned layer or weakens the field acting on the
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