Read Back Signals in Magnetic Recording - Research Group Fidler

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2.8.3 Giant Magnetoresistance Effect Basics Giant magnetoresistance was first reported by Baibich et al. in 1988 [6]. They discovered that the resistance of Fe/Cr multilayers decreased 50% when they applied a magnetic field (see Figure 2.3). Figure 2.3: Giant magnetoresistance in Fe/Cr multilayers [18]. Without applying an external field the magnetic layers are antiparallel coupled. If a strong enough field is applied to align the magnetization of adjacent magnetic layers, the resistivity of the multilayers drops significantly. Thus resistivity is lower in case of parallel alignment and higher for the antiparallel configuration. Multilayers require very high saturation fields to overcome the strong antiferromagnetic coupling. Therefore the field sensitivity of such multilayers is actually lower compared to sensors using the AMR effect. These considerations motivated the invention of an alternative GMR structure for sensors shown in Figure 2.4. It consists of four main layers. There are two ferromagnetic layers which are separated by a nonmagnetic layer, called spacer layer (mostly Cu). All these layers are only few nanometers thick. The magnetization of one ferromagnetic layer is fixed via the exchange anisotropy of an antiferromagnetic layer (see Section 5.1.2). The magnetization of the other ferromagnetic layer can rotate freely and is therefore called free layer. In contrast to multilayer structures this structure does not show any hysteresis. 22
Basics Figure 2.4: Schematic model of a spin-valve GMR head (CIP mode) with exchange-pinned layer and longitudinal hard bias [19]. The change in resistance of the GMR effect can be mathematically approximated by following formula: ( θ θ ) ⎛ 1−cos 1− 2 ⎞ ρ = ρ0⎜1+ RGMR ⋅ ⎟ ⎝ 2 ⎠ (2.51) Figure 2.5 shows the dependence of the resistivity as function of the angle between the magnetization orientations of the two ferromagnetic layers. To achieve highest sensitivity, the working point of the GMR spin valve should be chosen at maximum slope. If there is no external field, the magnetization of the free layer should be ideally perpendicular to the pinned layer magnetization. To adjust the magnetization of the free layer, hard bias magnets are used as shown in Figure 2.4. Figure 2.5: Change in resistance of a spin valve compared to AMR (NiFe) vs. magnetization orientation [19]. 23
Page 1 and 2: DIPLOMARBEIT Read Back Signals in M
Page 3 and 4: Abstract This thesis concentrates o
Page 5 and 6: Contents 3.2.4 Signal of Written Bi
Page 7 and 8: Introduction 1 IntroductionEquation
Page 9 and 10: Introduction In 1955, before the RA
Page 11 and 12: 2 BasicsEquation Section (Next) 2.1
Page 13 and 14: Basics curl H = 0 . (2.15) So H is
Page 15 and 16: Basics This is justified, because t
Page 17 and 18: Basics Here J ij represents the exc
Page 19 and 20: s Basics ∂J α ∂J =−γ J× He
Page 21: Basics for spin down electrons. An
Page 25 and 26: Basics channels in the parallel and
Page 27 and 28: Basics Nowadays there are again eff
Page 29 and 30: Analytical Calculations 3 Analytica
Page 31 and 32: Analytical Calculations developing
Page 33 and 34: Analytical Calculations t C 8 π =
Page 35 and 36: µ 0 Hsig [T] 0.030 0.025 0.020 0.0
Page 37 and 38: Analytical Calculations n n ⎛HH,
Page 39 and 40: z Analytical Calculations Figure 3.
Page 41 and 42: 4 Numerical MethodsEquation Numeric
Page 43 and 44: Numerical Methods ϕ ( x ) =δ . (4
Page 45 and 46: Numerical Methods current flowing o
Page 47 and 48: Numerical Methods ∫ ∫ ∫ si =
Page 49 and 50: Numerical Methods Figure 4.2: The l
Page 51 and 52: Numerical Methods j =−σgrad Φ.
Page 53 and 54: Numerical Methods within the volume
Page 55 and 56: Numerical Methods Integration of Am
Page 57 and 58: 4.5 Time integration Numerical Meth
Page 59 and 60: 5 Read Head DesignEquation 5.1 Bias
Page 61 and 62: Read Head Design The exchange bias
Page 63 and 64: Read Head Design free layer (see Fi
Page 65 and 66: FEM Simulations 6 FEM SimulationsEq
Page 67 and 68: FEM Simulations Magnetic Material J
Page 69 and 70: 6.2 Results FEM Simulations In the
Page 71 and 72: Output [V] 0.108 0.107 0.106 0.105
Page 73 and 74:
FEM Simulations has a greater influ
Page 75 and 76:
Output Voltage [V] 0.1074 0.1072 0.
Page 77 and 78:
7 OutlookEquation Section (Next) Ou
Page 79 and 80:
Appendix A In case we have the func
Page 81 and 82:
Appendix B Moreover the second inte
Page 83 and 84:
List of Figures List of Figures Fig
Page 85 and 86:
List of Figures Figure 6.1: The mag
Page 87 and 88:
Bibliography [11] H. Katayama, M. H
Page 89 and 90:
Bibliography [38] W. F. Brown Jr.,
Page 91:
Lebenslauf Otmar Ertl Reinprechtsdo
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