Read Back Signals in Magnetic Recording - Research Group Fidler

6.2 Results
FEM Simulations
In the following the results of the simulations are presented. Naturally the model described
above of a read head is not perfect at all. It was not the target to design a perfect read head,
but to be able to simulate the read back process. Although the used read head model is not
technically mature, the results of the simulations show qualitative accordance with reality.
6.2.1 Equilibrium State
Ideally the magnetizations of the pinned and the free layer should be perpendicular to each
other in equilibrium state, so that the magnetization of the pinned layer shows in z-direction,
and that of the free layer in y-direction. Then the total resistance would be 32.87 Ω and the
potential difference 98.6 mV. In reality such a perfect configuration is not achievable.
The equilibrium states of our model for the two different current directions are shown in
Figure 6.4. For the more favorable current direction the magnetizations are almost
perpendicular to each other in the center of the GMR element. Unfortunately the free layer
magnetization is twisted downwards due to the demagnetizing field of the pinned layer.
Similarly the pinned layer is rotated in the same direction due to the hard bias. Both effects
lead to an asymmetric transfer curve (see Section 6.2.2).
Figure 6.4: The normalized magnetization of the free layer and the pinned layer in
equilibrium state for the two different current directions. The color code gives the zcomponent
of the normalized magnetization, red corresponds to the positive and blue to the
negative z-direction. Thus the red arrows represent the pinned layer magnetization. The
right hand side gives the configuration for the more favorable current direction, because
here the current field cancels partially the demagnetizing field of the pinned layer.
69