Read Back Signals in Magnetic Recording - Research Group Fidler

FEM Simulations
The sense current through the spin valve is applied at the lateral surfaces of the conductor
model and has a value of 3 mA.
The effective conductivities of the individual parts are estimated from the measured
conductivities in Figure 6.3 [37]. These conductivities differ much from the bulk values,
because the electron mean-free path is larger than the layer thicknesses.
Figure 6.3: The effective conductivities for a typical spin valve taken from [37].
In our simulation the free layer has a conductivity of
PL 6 −1 −1
σ = 3.5⋅10 Ω m , the Cu layer
FL 6 −1 −1
σ = 310 ⋅ Ω m , the pinned layer
Cu 6 −1 −1
σ = 4.5⋅10 Ω m , the antiferromagnet
AF 6 −1 −1
Lead 7 −1 −1
σ = 110 ⋅ Ω m and finally the leads σ = 110 ⋅ Ω m . Here the conductivities of free
layer, pinned layer and the Cu layer are not constant, because it is assumed that these layers
contribute to the GMR effect. Their maximum change in conductivity, the GMR ratio, was
assumed to be 10%. So the effective GMR ratio of the whole layer structure is smaller,
because the sense current is shunted by the antiferromagnet. All values assumed for the
conductor model are listed in Table 6.2.
Conductor σ [Ω -1 m -1 ] Type MR-Ratio Magnetic Material 1 Magnetic Material 2
Free Layer 3.0E6 2 (GMR) 0.1 Free Layer Pinned Layer
Cu Layer 4.5E6 2 (GMR) 0.1 Free Layer Pinned Layer
Pinned Layer 3.5E6 2 (GMR) 0.1 Free Layer Pinned Layer
Antiferromagnet 1.0E6 0 - - -
Lead 1.0E7 0 - - -
Table 6.2: The properties for all parts of the conductor model. Here the conductivities, the
type of magnetoresistance, and the magnetic materials, which influence the conductivity,
are given. (Compare with Table 4.1).
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