Read Back Signals in Magnetic Recording - Research Group Fidler

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FEM Simulations 5.1.4, are used in modern spin valves.) The transfer curve and the slope at zero point do not differ much compared to the low exchange bias field. However, for large fields we have a much better sensor performance in respect to sensitivity and symmetry. The higher voltage in equilibrium is due to the larger angle between both magnetizations. The large exchange bias field reduces the deflection due to the hard bias, while the free layer magnetization stays unmodified, because of the widely unchanged demagnetizing field of the pinned layer. 6.2.3 Influence of Shields Now the shields are taken into account. It is expected that the shields have an influence on the transfer curve due to the mirror currents (see Section 5.1.5). Indeed the shields have a large influence. Again the transfer curve is evaluated by applying the external field shown in Figure 6.5 on the GMR element. The shields are not exposed to the external field. The result is given in Figure 6.7. Output Voltage [V] 0.109 0.108 0.107 0.106 0.105 0.104 0.103 0.102 -0.10 -0.05 0.00 0.05 0.10 H z [T] ΔR/R [%] without shields with shields -0.10 -0.05 0.00 0.05 0.10 H z [T] Figure 6.7: The transfer curves for the spin valve with and without shields (for both Hexch = 0.1 T). The presence of shields generally leads to a greater output voltage, particularly at zero field. The origin of this effect is based on mirror currents. They reduce the current field which works against the demagnetizing field of the pinned layer. Therefore the demagnetizing field 2 1 0 -1 -2 -3 -4 -5 72
FEM Simulations has a greater influence. The result is a more likely antiparallel state, which is equivalent to a higher total resistance. This proves that the shield also have an influence on the read head behavior and cannot be neglected in micromagnetic simulations. 6.2.4 Relaxation The micromagnetic behavior of the GMR sensor depends on the Gilbert damping constant. Starting from an equilibrium state with an external field of H ext = 0.03 T in positive z- direction, the relaxation to the new equilibrium state when suddenly switching off the field, is shown in Figure 6.8. Output Voltage [V] 0.1060 0.1055 0.1050 0.1045 0.1040 0.1035 0.1030 0.0 0.2 0.4 0.6 0.8 Time [ns] α = 0.1 α = 0.2 α = 0.3 α = 0.5 α = 1 Figure 6.8: The output signal over time for a relaxation from equilibrium state with Hext = 0.3 T to the equilibrium state without field for different Gilbert damping constants. For large Gilbert damping constants we have strong damping, resulting in a quite large relaxation time (larger than 0.4 ns). New read heads work with a read frequency up to 2 GHz. Therefore such large relaxation times would weaken the read back signal. Fortunately realistic damping constants are about α ∼ 0.1, which lead to an undercritical damping, resulting in damped oscillations. Smallest relaxation times are achieved for critical damping with damping constants around 0.3. 73
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DIPLOMARBEIT Read Back Signals in M
Page 3 and 4:
Abstract This thesis concentrates o
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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
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2 BasicsEquation Section (Next) 2.1
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Basics curl H = 0 . (2.15) So H is
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Basics This is justified, because t
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Basics Here J ij represents the exc
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s Basics ∂J α ∂J =−γ J× He
Page 21 and 22: Basics for spin down electrons. An
Page 23 and 24: Basics Figure 2.4: Schematic model
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: Output [V] 0.108 0.107 0.106 0.105
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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Read Back Signals in Magnetic Recording - Research Group Fidler

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