Read Back Signals in Magnetic Recording - Research Group Fidler

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Introduction In the late forties and the early fifties the first computing machines where developed. To store program and data information punched paper cards or punched paper tapes where used. Later magnetic tape recording was used, which had a big disadvantage. The random data request of tapes was very time consuming, because the non-sequential access required long rewind and fast-forward times. That is why there was the demand for a fast random access storage system. In the late 1940s a new computer design program started at the University at Berkeley to develop an intermediate sized computer based on a magnetic drum memory. To get rapid data access, high rotational speeds were used, which generated interest in non-contact recording heads. Among the tested head designs, there was also a head with a wide gap and a drum with a soft magnetic layer beneath the usual magnetic layer, the so called Soft-Under-Layer (SUL). The result was that the magnetite dipoles were oriented perpendicular to the surface and not along the surface circumferentially [3] (1949). In 1956 IBM announced the first commercial magnetic disk drive, the Random Access Method of Accounting and Control (RAMAC) 350. This drive had a storage capacity of 5 MB and a data density of 2 kbit/in 2 . 50 24-in aluminum disks coated with iron oxide paint acted as media. The whole stack of disks had a weight of 250 kg. Air pressure held the distance of 25 µm between head and disk. The complex air pressure mechanism was very expensive. That is why only one actuator-arm assembly with a head pair - one for the upper surface and one for the lower surface of a disk - was used (see Figure 1.2). Nevertheless the access time was less than a second. Figure 1.2: The first computer disk drive RAMAC. The pneumatically driven actuator arm and some of the 50 disks are visible [4]. 8
Introduction In 1955, before the RAMAC was announced, IBM decided to start the development of the next generation hard disks. The targets of the so called Advanced Disk File (ADF) project were a 10 times larger capacity and a 1/10 the access time compared to RAMAC. The faster access time could only be reached by using one head for each disk surface. It was clear that the uneconomic air pressure system had to be replaced by flying heads (air bearing sliders). Flying heads allow a smaller head-disk spacing, which finally allows higher linear data densities. The experiences of the RAMAC lead to the decision to use a harder media. They chose soft magnetic steel disks. Oxidizing in a steam atmosphere leads to a hard thin layer on their surface. In addition the manufacturing costs were less than that of RAMAC’s aluminum disks. The project was very risky, because of lacking knowledge about air bearing heads and about perpendicular recording. In 1960, due to several failures and major problems (e.g. the surface quality of the steel disks was unacceptable), IBM turned away from perpendicular recording and towards longitudinal recording. Due to major achievements in longitudinal recording perpendicular recording became uninteresting for many decades. All magnetic storage devices were using coils to read out magnetic information. In 1971 however, a new type of transducer using the anisotropy magneto-resistance effect (AMR) was reported by R. B. Hunt [5]. AMR heads generate larger read back signals than inductive heads for common relative velocities between disk and head. Another advantage of AMR heads over inductive heads is their lower resistance and inductivity resulting in lower Johnson noise. In 1991 the first commercial hard disks using AMR read heads were available and broke the 100 Mbit/in 2 recording density barrier. In 1988 Baibich et al. [6] discovered a new magneto-resistance effect. Due to its large change in resistance compared to AMR this effect was called Giant Magneto-Resistance (GMR). GMR read heads were first introduced in commercial hard disks by IBM in 1997. The invention of AMR and GMR read heads has accelerated the growth in data density (see Figure 1.3). 9
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: Introduction 1 IntroductionEquation
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 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
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5 Read Head DesignEquation 5.1 Bias
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Read Head Design The exchange bias
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Read Head Design free layer (see Fi
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FEM Simulations 6 FEM SimulationsEq
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FEM Simulations Magnetic Material J
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6.2 Results FEM Simulations In the
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Output [V] 0.108 0.107 0.106 0.105
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FEM Simulations has a greater influ
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Output Voltage [V] 0.1074 0.1072 0.
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7 OutlookEquation Section (Next) Ou
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Appendix A In case we have the func
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Appendix B Moreover the second inte
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List of Figures List of Figures Fig
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List of Figures Figure 6.1: The mag
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Bibliography [11] H. Katayama, M. H
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Bibliography [38] W. F. Brown Jr.,
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Lebenslauf Otmar Ertl Reinprechtsdo
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Read Back Signals in Magnetic Recording - Research Group Fidler

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