Read Back Signals in Magnetic Recording - Research Group Fidler

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Basics There are two different modes a spin valve can be operated, the current-in-plane (CIP) mode, and the current-perpendicular-to-plane (CPP) mode. The difference between these two modes is the current direction. In the first case the sense current is parallel to the layers of the GMR element, while for the second case the current is applied perpendicular to the layers. The two different modes are illustrated in Figure 2.6. 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]. Up to now only the CIP configuration is used in commercial hard disks. For smaller read head designs the CPP mode becomes more and more interesting, because the output voltage for CPP heads is roughly inversely proportional to the square root of the sensor area. In addition the change in resistance is higher, because the sense current is not shunted by the conductive spacer layer, which does not contribute to magneto-resistance. Besides the CPP structure allows smaller read gaps, thus smaller distances between the two shields, because the shields can be used as leads. This design allows read gaps down to 20 nm, compared to 60 nm for CIP heads. CPP heads are thermally more stable, because the layer structure is in contact to the relative large shields leading to a better heat dissipation. The origin of the GMR effect is the spin dependent scattering of FM/NM/FM multilayers. The spin dependent scattering at interfaces is the main contribution. Figure 2.7 shows a schematic picture of the potential landscape of a GMR layer structure for the two spin 24
Basics channels in the parallel and in the antiparallel state, indicating the different origins of scattering. Only deviations from the periodic atomic potentials are shown, as no scattering takes place in a regular periodic lattice. The size of the potential step and of the scattering potentials at imperfections of the interfaces depends on the degree of matching of the electronic structures of the ferromagnetic layers and the nonmagnetic spacing layer. In order to obtain a large GMR ratio, good electronic structure matching is required for one spin direction and bad matching for the opposite spin direction. It is clear that giant magnetoresistance only occurs in layers with thicknesses much smaller than the electron mean-free path. 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]. The GMR effect can be qualitatively described by a very simplified two current model. The current densities are assumed to be homogenous for both spin directions. If the resistances for the ‘+’ and ‘-‘ channels in the parallel state are denoted with R + and R − , then the total resistance for the parallel state is 25
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 and 22: Basics for spin down electrons. An
Page 23: Basics Figure 2.4: Schematic model
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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Read Back Signals in Magnetic Recording - Research Group Fidler

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