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Magnetics, IEEE Transactions on

Issue 2  Part 1 • Date March 1999

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Displaying Results 1 - 25 of 71
  • Conference Author Index

    Page(s): 813 - 814
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  • Conference author index

    Page(s): 1011 - 1012
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  • Design of a hybrid fluid bearing system for HDD spindles

    Page(s): 821 - 826
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    This paper introduces a novel design of hybrid hydrodynamic and aerodynamic fluid bearing system. The fluid bearing system consists of an oil lubricated journal bearing unit with herringbone grooves and an air lubricated thrust bearing unit having a conical thrust plate engraved with spiral grooves. This bearing system has lower power consumption and enables a reliable seal design only for its journal bearings. The spindle motor with this bearing system has been prototyped. In this paper some simulation and testing results are reported View full abstract»

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  • Spin valve and dual spin valve heads with synthetic antiferromagnets

    Page(s): 655 - 660
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    Analytical and micromagnetic analysis have been performed for synthetic antiferromagnet (SAF) biased single and dual spin valve heads. It is found that for a un-pinned SAF under an external field, the antiparallel axis will flop to the direction orthogonal to the field direction. Introducing a thickness differential in the SAF can help to prevent the magnetization flop in addition to the exchange pinning. Design principles for SAF biased single and dual spin valve heads are presented. An SAF biased dual spin valve head with appropriate design can have significant advantages over the single spin valve besides higher GMR values View full abstract»

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  • New frequency domain method of nonrepeatable runout measurement in a hard disk drive spindle motor

    Page(s): 833 - 838
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    A new frequency domain method was developed and mathematically investigated for measurement and analysis of runout in a computer hard disk drive (HDD) spindle motor. Repeatable runout (RRO) can be represented as the harmonics of the motor rotational frequency in frequency domain. Therefore nonrepeatable runout (NRRO) is the subtraction of the harmonics from total indicated runout (TIR), so that NRRO in time domain can be easily reconstructed by inverse Fourier transform of NRRO in frequency domain. This method is accurate and simple without index signal indispensable to time domain analysis. This research measured runout of a 3.5" HDD spindle motor with both capacitance probe and laser, and also investigated its characteristics statistically and correlated NRRO with defect frequencies of ball bearing, resonance frequency and its mode shape through Campbell diagram View full abstract»

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  • Evaluation system for residual vibration from HDD mounting mechanism

    Page(s): 868 - 873
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    An evaluation system for calculating the residual vibration caused by a HDD (Hard Disk Drive) mounting system is presented. It contains both the elements for measurement and analysis. The PES (Position Error Signal) of an ideally balanced rigid rotary actuator depends on the rotational vibration of the HDD, specifically at lower frequencies. First, this evaluation technique obtains a measurement of the transfer function of the HDD rotational acceleration over actuator current. Next, using the measured power spectrum of the actuator in combination with the HDD's tracking error transfer function, the response of the entire HDD and mount system is calculated in the frequency domain. Finally the time domain system response is calculated by computation of the Inverse Fast Fourier Transform (IFFT) of the frequency response solution, assuming a random phase of the input force. Good correlation is obtained between measured and calculated system responses. Experimental result show that the dominant residual vibration is caused by the mounting mechanism response and that both the HDD and HDD mount system need to be evaluated and understood as a system, in order to achieve higher TPI (Track per inch) in the future View full abstract»

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  • Tribo-chemistry at the head/disk interface

    Page(s): 910 - 915
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    Tribo-chemical studies at the head/disk interface (HDI) were conducted on hydrogenated (CHx), nitrogenated (CNx), and cathodic-arc amorphous hard carbon disk samples coated with perfluoropolyether ZDOL and X1P/ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3-TiC sliders and thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber followed with a surface chemistry analysis by X-ray Photo Emission Electron Microscopy (X-PEEM) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The friction and catalytic decomposition mechanisms of ZDOL are described, as well as the tribo-chemical performance of cathodic-arc carbon overcoats coated with ZDOL, and data demonstrating the chemical alteration of the lubricant and carbon overcoat are also presented View full abstract»

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  • Thermal asperity trends

    Page(s): 752 - 757
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    A thermo-mechanical model that predicts the changes in thermal asperities as a function of increasing areal density is described. Conceptually, the problem is divided into two portions: the collision and relative motion of an asperity along the slider, and the subsequent diffusion of thermal energy into the head in the vicinity of the read element. The former is treated using a quasi-static spring model for the various mechanical degrees of freedom; the later with a scaling model for the heat transfer. The thermal model was verified by using a focused fast laser pulse to simulate a thermal transient at the read element. The predictions of the full model were also compared with measured thermal asperities that were produced on a spin-stand. The results support one of the model's main predictions: a significant increase in the amplitude of worst case thermal asperity events can be expected in the next few years View full abstract»

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  • A novel sensitivity function for MR heads and an application

    Page(s): 661 - 666
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    A two-dimensional sensitivity function, describing the down-track and cross-track responses of a MR head, is derived starting from a microtrack formed with a maximal-length pseudo random binary sequence (PRBS). This sensitivity function is built up from a set of `extracted dipulse' responses each taken with the readback head in a different off-track position with respect to the microtrack. The resulting two-dimensional function represents the sensitivity to a `unit magnet' with a length of one channel bit, rather than to the vertical field component alone. There are two advantages to this approach: first, the sensitivity to high frequency signal components is much enhanced and the signals used are generally much more representative of written data. Second, this method has the ability to quantify both linear and nonlinear readback distortions as a function of off-track position. This paper initially describes the practical procedure used to obtain the sensitivity function. An advantage of this procedure is that you do not need to have a clock channel for the timing alignment of the dipulses as they are already tied to the bit-cell positions. In the latter half of the paper, this procedure is used to analyze the effects of “read-write non-parallelism” a condition wherein, the MR stripe reads the transitions at a skew due to a manufacturing defect or otherwise. In other words, it is probed whether a cross-track variation in head sensitivity would contribute towards the so-called “deterministic off-track peak jitter” and also whether a relative skew between read and write operations can influence the head sensitivity function and aggravate the deterministic peak-jitter. The answers we got for both the questions were in the negative. There was no deterministic trend in peak-position variation (as against the trends that we got with full-width tracks) with or without a skew and the head sensitivity function was also not affected by a skew View full abstract»

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  • Beyond 10 Gb/in2: Using a merged notched head (FIB-defined writer and GMR reader) on advanced low noise media

    Page(s): 695 - 699
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    We demonstrated recording performance at greater than 10 Gb/in2 with data rates up to 25 MB/s, using a single combined write and read head (Merge Notched head) View full abstract»

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  • Characterization of the head-disk interface at nanometer dimensions

    Page(s): 764 - 769
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    Characterization of the head and disk surfaces at nanometer dimensions is crucial for optimizing the tribological performance of the head-disk interface as discussed in the following examples given in this paper. Friction mapping at a nano-scale is used to study the nucleation sites of smears on a disk from a failed drive showing high nonrecoverable error rate at the OD. Nanoindentation data suggest that the hardness of the alumina grains is comparable to that of the TiC grains. Al2O3-TiC substrates from vendor B exhibit the lowest hardness of 30 GPa. During the CSS test, sliders with vendor B Al2O3-TiC substrates exhibit relatively greater amount of wear debris and grain pullouts as compared to those of the vendors A and C. The nature of the damage to the DLC coating during nanoscratching can be qualitatively correlated to hardness, toughness, high residual stresses, and weak adhesion due to an impurity at the coating-substrate interface. The correlation between the highest nanowear resistance and best CSS wear performance of DLC coatings indicates that the wear properties at a nanoscale can be used as an indirect measure of the CSS performance of the carbon overcoats View full abstract»

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  • Electrostatic microactuator and design considerations for HDD applications

    Page(s): 1000 - 1005
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    A flexure-based rotary electrostatic microactuator is described. This microactuator is for application in a high track-density hard disk drive (HDD). It is fabricated using a high aspect-ratio stencil electroplating process. This paper emphasizes the practical system-level issues that affect the device design. The micro-actuator is demonstrated in a 3.5" form-factor HDD. With a servo bandwidth of 5 kHz, a one-track seek can be completed in under 0.2 ms. This batch-fabricated electro-static microactuator provides a low-cost, high-performance solution for achieving very high track-densities View full abstract»

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  • Fe-based alloy laminated films with crossing easy axis structure and their applications to laminated film heads for high-frequency use

    Page(s): 723 - 728
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    To realize laminated film heads with superior recording and reproducing capability in high frequency region, we have investigated Fe-based alloy (Bs=1.6 T) laminated films with different laminating structures: one with magnetostatically coupled laminated films and the other with laminated films having crossing easy axis structure. Although the magnetostatically coupled Fe-based laminated films show high initial permeability even in a narrow shape area near the magnetic gap, they have anisotropic initial permeability, and therefore the laminated film head using this film shows lower playback output compared with conventional Go-based amorphous film head below 20 MHz. The Fe-based laminated film with crossing easy axis structure with 5 nm SiO2 shows isotropically high initial permeability in high frequency region and maintains high initial permeability even in a narrow shape area near the magnetic gap. Consequently, the laminated film head using this film shows excellent recording and reproducing characteristics for metal particle tape (MP-tape) for wide frequency ranges View full abstract»

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  • In-situ Lorentz microscopy studies of spin-valve structures

    Page(s): 788 - 793
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    Lorentz electron microscopy, including a quantitative magnetisation-mapping technique, has been used to study the local magnetisation reversal mechanism in active spin-valve devices for correlation with the giant magnetoresistance and domain structure. Varying various parameters such as device size, applied current value and direction of easy-axis have been found to have an effect on the magnetisation reversal mechanism and on the GMR curve View full abstract»

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  • Second Asia-Pacific Magnetic Recording Conference (APMRC'98)

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    The conference focused on design and manufacturing aspects of hard disk drive technology. The presentations were organized into six sessions and covered the design of spindle, bearing, motor, hard disk drive/actuator and servo. There were also sessions on head-disk interface, tribology and manufacturing technology. The final session of the conference was on the newly emerging technology of microactuators View full abstract»

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  • High precision manufacturing cell for motor bearing components

    Page(s): 963 - 967
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    This paper briefly describes some of the advanced machine tool technology used in the design of an automated high precision manufacturing cell “DeltaTurn 40”, designed to meet the needs of the hard disc drive industry. Key features of the machine used to ensure lasting precision and speed of operation will be discussed. Results of extensive cutting trials on various ferrous and non-ferrous materials are used to show the machines achievable part precision. These are given in terms of Cpk values, surface finish quality, roundness, flatness and machining parameters used View full abstract»

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  • Experimental investigations of asperity compliance of flexible magnetic medium

    Page(s): 770 - 775
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    Three-color interferometry was used to investigate the deformation of asperities on flexible medium surfaces. Elastic asperity compliance curves were obtained to evaluate changes in surface roughness due to burnishing, determine mechanical properties of flexible medium and analyze differences between single layer and dual layer metal particle tapes. Asperity compliance curves were obtained for metal particle tapes with different substrate properties and substrate thickness. A power function was used to fit the asperity compliance measurements and to calculate the contact pressure at the head/medium interface View full abstract»

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  • A comprehensive time domain simulation tool for hard disk drive TPI prediction and mechanical/servo enhancement

    Page(s): 879 - 884
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    A comprehensive time domain simulation tool has been developed to provide a realistic simulation of hard disk drive track following servo performance. It serves as a “virtual drive” which allows the prediction of achievable TPI for future products, and off-track shock/vibration characteristics with a given mechanical platform and servo controller. It also provides a convenient tool for enhancing mechanical and servo designs. The simulation tool has three main modules. The methodology used in identifying them is detailed. The simulator was developed based on drive level and component level measurement of position error signal (PES) and mechanical vibrations, and an electrical noise recovery scheme. Simulation and experimental results have been used to evaluate the accuracy of the simulator View full abstract»

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  • Theoretical analysis of a ball bearing used in HDD spindle motors for reduction of NRRO

    Page(s): 845 - 850
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    In this paper, we theoretically analyzed the NRRO of the ball bearing caused by form errors of the inner and outer raceways and balls. The results are summarized as follows: (1) as for geometrical errors of the inner and outer raceways, it is possible to reduce the NRRO to less than 1 nm by choosing either 12 or 18 balls, even if the inner and outer raceways have harmonic undulation of less than the eleventh order; (2) the effect of the differences in ball diameter and ball form error on the NRRO monotonously decreases as the number of balls increases View full abstract»

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  • Taming disk/spindle vibrations through aerodynamic bearings and acoustically tuned-mass dampers

    Page(s): 827 - 832
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    This paper studies the feasibility of suppressing the vibration of a spinning disk/spindle system by creating an aerodynamic bearing between the spinning disks and adjacent stationary flat surfaces. An automated impact hammer was first developed and instrumented to obtain repeatable and consistent frequency response functions (FRF). Through this device, frequency response functions of a 5-platter disk/spindle system were measured in the air and in the vacuum up to 7200 rpm with and without an air bearing, which consists of a flat surface 0.635 mm (25 mils) away from the top spinning disk. Compared with the experimental results in vacuum, the presence of the air (without the air bearing) causes the resonance frequencies of the disk/spindle system to split resulting in smaller resonance amplitudes. Nevertheless, the splitting does not increase the modal dampings of the disk/spindle system. When the air bearing is present, the air bearing does not further reduce the resonance amplitudes, but it does increase the modal dampings by 100-200%. Moreover, the presence of the air bearing lowers the resonance frequencies by 3%, because the air in the bearing behaves like incompressible fluid adding considerable inertia to the disk/spindle system. Also, the increase in damping and shift in natural frequencies are independent of the rotational speed. Finally, combination of the air bearing and a tuned-mass damper can significantly reduce the resonance amplitudes by 50-75% View full abstract»

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  • Dual-stage actuator system for magnetic disk drives using a shear mode piezoelectric microactuator

    Page(s): 988 - 992
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    We developed a novel piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. This microactuator is based on the shear deformation of piezoelectric elements, and drives the head suspension assembly. The actuator is suitable for thin devices, and is easily manufactured because of its simple stack configuration. We installed the microactuator in a 2.5" prototype drive, and evaluated the servo system of the dual-stage actuator. This paper describes the structure of our piezoelectric actuator, its mechanical characteristics, and the evaluation of the dual-stage actuator servo system View full abstract»

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  • Precision positioning using a microfabricated electrostatic actuator

    Page(s): 993 - 999
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    This paper presents a microfabricated actuator designed for high precision servo-positioning in a magnetic hard disk drive. The device is actuated using electrostatic force generated with parallel-plate capacitive electrodes. The displacement of these electrodes is measured using a dedicated capacitive sensing interface, allowing closed-loop control to be used to extend the servo bandwidth. Using the sensing electronics and a simple phase-lead compensator, a prototype device was used to actuate a 1.6 mg ceramic slider over a 1.2 kHz bandwidth. Using optical position measurements, the same actuator was used to achieve a 2.5 kHz bandwidth View full abstract»

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  • Nanosecond and sub-nanosecond writing experiments

    Page(s): 625 - 631
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    This paper explores the high speed and high power aspects of fast writing in magnetic data storage. It describes the experimental methods and instrumentation needed to exercise thin-film write heads at excessively large write currents (<0.5 A), short pulse durations (⩾200 ps) and high frequencies (<1 GHz). The instrumentation used is discussed in detail (avalanche pulse generator, head interconnect circuit). The thermal behavior of the head is investigated to ensure that the temperature of the hottest yoke leg (P2) does not exceed 250°C to avoid thermal degradation of the magnetic performance. The paper describes various pulse write, AC-bias write and AC-burst erase methods. As an example, experimental results obtained for an “industry-typical” head are reported and discussed, viz head footprints, saturation curves, write current needed for media magnetization reversal down to 200 ps, write field gradients, write field growth rates, high-frequency head efficiency, current levels needed for AC erasure versus frequency, and AC-bias writing results View full abstract»

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  • Transition curvature analysis

    Page(s): 619 - 624
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    On-track recording losses associated with transition curvature in a merged magnetoresistive-read/inductive-write recording system were investigated. Variations in write head design resulted in a wide variation of reproduced pulse width. Magnetic force microscope (MFM) observation of written tracks revealed that transition curvature was related to the pulse width variation. The effect of transition curvature is modeled as a separable loss function by convolving a reader cross-track sensitivity function with a cross-track phase delay profile. Curvature loss has a different spectral content than transition broadening, allowing us to separate the two effects by comparing discrete Fourier transforms of isolated pulses. Results of such an analysis agree satisfactorily with MFM measurements. Planarization of mid-shields had minimal impact on the pulse width, but a notched write head design mitigated the effect. Transition curvature must be taken into account during write head design and in decisions regarding relative read and write widths View full abstract»

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  • An explanation of the observed frequency domain behavior of head-disk interface resonances in the proximity recording regime

    Page(s): 933 - 938
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    Magnetic head-disk interfaces (HDI) which are designed so that the mechanical spacing, between the magnetic recording head and spinning disk media, is so small that frequent intermittent contacts occur during normal steady state operation, can be said to be operating in the “proximity” recording regime. Mechanical spacing (“fly height”) modulation, with characteristic frequency well above the estimated air bearing resonance frequencies, but well below slider ringing frequencies, has been observed in the proximity recording regime. In this paper, the effect of slider preload change, and the effect of atmospheric pressure change, on the frequency and amplitude of such fly height modulation, as measured using laser Doppler vibrometry, is reported. A simple analytical model was developed to explain the existence of the modulation and its observed dependence on applied gram load View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology