Read Back Signals in Magnetic Recording - Research Group Fidler

Analytical Calculations
developing of the magnetic potential Ψ between the shields and the sensing layer at the ABS.
The magnetic potential is assumed to vanish at the ABS of the shields due to their high
permeability.
⎧ 1 x < t/2
⎪
⎪ g+ t/2+ x
Ψ ( x,0) = C⋅MSL ⋅⎨ t/2 ≤ x < g+ t/2
⎪ g
⎪
⎩
0 g+ t/2≤ x
Figure 3.2: The magnetic potential at the ABS under Karlquist approximation.
This function is shown in Figure 3.2. The amplitude of this function is proportional to the
magnetization of the sensing layer. The magnetization of the sensing layer can be replaced by
(3.5)
top
face charges m 0 SL M σ =μ at the bottom and bottom
m 0 SL M
σ =−μ at the top side under the terms of
(2.19). The top face charge can be neglected, because the sensing layer height is usually much
larger than the distance between ABS and data layer surface. Common flying heights are
about 10 nm. The magnetic charge at the bottom side leads to a jump of the magnetic field
H − H =− M . Due to the symmetry of the surface charge in the near region
in out
z z SL
z
H (0,0) = M / 2
(3.6)
H SL
Ψ(x,0)
C⋅MSL
-t/2-g -t/2 t/2 t/2+g x
can be assumed. This is the necessary condition, which allows the determination of the
unknown proportional factor C in (3.5).
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