Read Back Signals in Magnetic Recording - Research Group Fidler

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Analytical Calculations The head velocity influences the bit quality. The higher the velocity, the worse the quality of the bit transitions is. For both data layer structures the read back signals were calculated. Again a head with 60 nm gap, 5 nm free layer, and a flying height of 10 nm was assumed. The spontaneous magnetization of the data layer was again J s = 0.5 T , but the data layer thickness was 12 nm. Figure 3.6 show smaller amplitudes for the effective field compared to the amplitude of the perfect transition. The worse transition quality of the faster written bits leads to a smaller signal. µ 0 Hsig [T] 0.020 0.015 0.010 0.005 0.000 -0.005 -0.010 -0.015 -0.020 0 50 100 150 x [nm] 200 250 300 µ 0 Hsig [T] 0 50 100 150 200 250 300 x [nm] 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. 3.3 Perpendicular Recording For perpendicular recording we can use the reciprocity principle again. We only have to take the SUL into account (see Figure 3.7). Analogically to the shields the SUL is also assumed to have infinite permeability. Then the problem is equivalent to assuming a second read head, mirrored at the SUL surface as shown in Figure 3.7 [22]. In addition the two shields with their high permeability act as second mirror. Therefore the head field for perpendicular recording can be approximated by a series expansion of head fields of the original head and its reflections at the SUL surface and the ABS. If the distance ABS to SUL is denoted with L, the series expansion of the head field for the perpendicular case can be written using (3.17) 0.020 0.015 0.010 0.005 0.000 -0.005 -0.010 -0.015 -0.020 36
Analytical Calculations n n ⎛HH, x( x, z− 2 iL) + HH, x( x, −z− 2( i+ 1) L) ⎞ ∞ ⎜ ⎟ n H H ( xz , ) = ∑⎜0 ⎟. (3.21) k = 0 ⎜ n n HH, z( x, z−2 iL) −HH, z( x, −z− 2( i+ 1) L) ⎟ ⎝ ⎠ 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]. The headfield for perpendicular recording is shown in Figure 3.8. Here the gap was again 60 nm and the sensing layer thickness 5 nm. The flying height was assumed to be 10 nm and the distance ABS to SUL 20 nm. The series expansion was aborted after the first 10 terms. For perpendicular recording, where the data layer is mainly magnetized in z-direction, only H contributes to the signal field. So for perpendicular recording the signal field is n H , z approximately proportional to the magnetization of the data layer. In contrast to longitudinal recording the bits are detected and not their transitions. 37
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 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: µ 0 Hsig [T] 0.030 0.025 0.020 0.0
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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