Read Back Signals in Magnetic Recording - Research Group Fidler

List of Figures
List of Figures
Figure 1.1: The original drawing of Oberlin Smith (1888) and Valdemar Poulson’s
telegraphone [2].................................................................................................................7
Figure 1.2: The first computer disk drive RAMAC. The pneumatically driven actuator
arm and some of the 50 disks are visible [4].....................................................................8
Figure 1.3: The development of bit sizes and storage densities over the last years [7]. ........10
Figure 2.1: a) Illustration of the damped precession of the magnetic polarization J
around the effective field Heff, taken from [15]. b) Influence of the Gilbert
damping constant on the field rise time in magnetic read heads. Head field
strength as a function of time for different Gilbert damping constants within the
head [43]. The dashed line depicts the current profile. The solid lines give the
head field for α = 1, 0.5, 0.1, and 0.02. The fastest field rise time is achieved with
intermediate damping (α = 0.5).......................................................................................20
Figure 2.2: The spin-split bands of a ferromagnet [18]..........................................................21
Figure 2.3: Giant magnetoresistance in Fe/Cr multilayers [18]. ............................................22
Figure 2.4: Schematic model of a spin-valve GMR head (CIP mode) with exchangepinned
layer and longitudinal hard bias [19]...................................................................23
Figure 2.5: Change in resistance of a spin valve compared to AMR (NiFe) vs.
magnetization orientation [19]. .......................................................................................23
Figure 2.6: The two different modes of a spin valve. The current is applied either
longitudinal (CIP) or perpendicular (CPP) to the layer structure [7]. .............................24
Figure 2.7: Potential landscape inside the FM/NM/FM active part of a spin-valve, for
the two spin channels in the parallel state (a,b) and in the antiparallel state (c),
indicating the different origins of scattering [20]............................................................25
Figure 2.8: A comparison of longitudinal recording and perpendicular recording [7]. .........27
Figure 3.1: A schematic 2-dimensional model of a read head for longitudinal
recording..........................................................................................................................30
Figure 3.2: The magnetic potential at the ABS under Karlquist approximation....................31
Figure 3.3: The x- and the z-component of the normalized head field of a read head
with 60 nm gap, and sensing layer thickness 5 nm, 10 nm below the ABS....................33
Figure 3.4: The effective signal field as function of the relative position of the read
head in respect to a perfect transition (Js = 0.5 T)...........................................................35
Figure 3.5: These two figures show the x-component of the magnetization (Js = 0.5 T)
of the data layer after a write process with head velocity 10 m/s (left) and 20 m/s
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