Read Back Signals in Magnetic Recording - Research Group Fidler

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R ↑↑ R+ R− = R + R + − Basics . (2.52) R+ + R− The resistance of both channels for the antiparallel configuration is set to resulting in 2 a total resistance of R + R = . (2.53) 4 + − R ↑↓ For the GMR ratio follows ( ) 2 R − R Δ R R − R ↑↓ ↑↑ + − = = . (2.54) R R 4R R ↑↑ + − This value is always positive, which means that the resistance in the anti-parallel configuration is higher than in the parallel configuration, which is consistent with (2.51). 2.8.4 Tunneling Magnetoresistive Effect Another magnetoresistive effect is the tunneling magnetoresistive (TMR) effect. The design of a TMR element is quite similar to a GMR element in CPP mode. The main difference is the insulating layer between pinned and free layer. The origin is also different, because TMR is due to spin dependent tunneling and not due to spin dependent scattering. With TMR elements changes in resistance up to 25% can be achieved at room temperature. The application in read heads is restricted because of the high resistance, which limits the operating frequency and causes Johnson and Shot noise. 2.9 Recording Schemes There are three possibilities to align the written bits in the data layer. Longitudinal to track, perpendicular to track, or transversal to the data layer called longitudinal, perpendicular and transversal recording respectively. Only first both recording schemes are of technical interest, because transversal written bits are hard to detect, because of their small stray fields. Although there were also attempts to use the perpendicular scheme in the early years, the longitudinal mode is well established and is used in all commercial hard disk drives. 26
Basics Nowadays there are again efforts to use perpendicular recording because of the theoretical higher data density limit. 2.9.1 Longitudinal Recording The principle of longitudinal recording is illustrated in Figure 2.8. For the writing process a ring head is used, which generates a stray field at the gap above the recording layer, so that it is magnetized in longitudinal direction. To retrieve the written information, the read head detects the stray field of the data layer, which has its maxima at the transitions of two opposite magnetized bits. In longitudinal recording the read back signal is roughly proportional to the first derivation of the magnetization. Figure 2.8: A comparison of longitudinal recording and perpendicular recording [7]. 2.9.2 Perpendicular Recording As shown in Figure 2.8 an additional soft magnetic underlayer is necessary for perpendicular recording. This soft under layer (SUL) closes the magnetic circuit. The yoke of the write head has a small write pole, which bundles the flux to achieve high writing fields, and a wide return 27
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: Basics channels in the parallel and
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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