Read Back Signals in Magnetic Recording - Research Group Fidler

List of Figures
(right). Red color represents magnetization in positive x-direction and blue color
magnetization in negative x-direction. The scale is in µm, thus the bit length is
approximately 40 nm. The data layer thickness is 12 nm. ..............................................35
Figure 3.6: The effective fields of the recording layers (shown in Figure 3.5) as
function of the head’s position. The dashed lines indicate the boundaries of the
recording layer model......................................................................................................36
Figure 3.7: The simplified read head model (left) for perpendicular recording. In the
right picture the mirror heads are indicated, which replace the SUL with its high
permeability [22]. ............................................................................................................37
Figure 3.8: The x- and the z-component of the normalized head field for perpendicular
recording..........................................................................................................................38
Figure 3.9: a) Application of Ampere’s Law on the dashed path, b) application of
Gauss’s Law on the dashed box. .....................................................................................39
Figure 4.1: Typical basis functions of two neighboring nodes of a 2-dimensional mesh......43
Figure 4.2: The left figure shows a set of 10 nodes after renumbering and the
clustering. The right figure shows the associated boundary matrix structure. The
large off-diagonal blocks, corresponding to far field interactions of two clusters,
can be approximated by low-rank matrices [25]. ............................................................49
Figure 4.3: Hϕ for an infinite long wire is plotted over the distance from the middle
axis. The second curve shows the error of the numerical calculation.............................55
Figure 4.4: The model of the coil (left). The color code shows the linear decrease of
the electric potential inside the wire. The chart (right) shows the magnetic field of
a solenoid in z-direction at the middle axis. The two dotted lines identify the
position of the solenoid. The second graph shows the relative error of the coil’s
magnetic field calculated with FEM calculation compared to the solenoid’s field. .......56
Figure 4.5: Schematic diagram of the simulation cycle. Adapted from [31]. ........................58
Figure 5.1: The shift of the hysteresis loop after a field cooling treatment of a
ferromagnetic/antiferromagnetic system [19] and the temperature dependence of
the exchange bias field for NiFe(4-8nm)/Cu(2.2nm)/CoFe(2nm)/IrMn(15nm) spin
valves with different free layer thicknesses [33].............................................................60
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]...................................................................................................................62
Figure 5.3: The effect of the sense current direction on the free layer (FL). For the first
case (left) the current field Hcurr partially cancels the stray field HS of the pinned
layer (PL) and weakens the exchange bias field Hexch. For the other current
direction (right) the stray field and the exchange bias field are supported by the
current field. ....................................................................................................................63
Figure 5.4: The layers of the GMR element also see mirror currents due to the high
permeability of the shields. The field of these mirror currents is able to reduce the
field of the original current at the free layer and the pinned layer. .................................63
84