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Magnetics, IEEE Transactions on

Issue 9  Part 2 • Date Sept. 2007

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Displaying Results 1 - 25 of 31
  • [Front cover]

    Page(s): C1
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    Freely Available from IEEE
  • IEEE Transactions on Magnetics publication information

    Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 3673 - 3674
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    Freely Available from IEEE
  • Message from the Conference Chair

    Page(s): 3675
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    The 22 invited papers were originally presented at the Asia Pacific Magnetic Recording Conference (APMRC) 2006, which took place from November 29 to December 1 in Singapore. View full abstract»

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  • Hard Disk Drive Reliability Modeling and Failure Prediction

    Page(s): 3676 - 3684
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    A reliability model for the hard disk drive (HDD) is developed, focusing on head-disk separation as the primary independent variable. The model is structured to incorporate the theoretical effects of environmental factors, plus empirical dependence on the product operating mode. An experimental method based on magnetic spacing loss theory is used to characterize the head-media separation as a function of temperature, altitude, humidity, and HDD operating mode. A statistical model based on these empirical data is developed to predict HDD reliability for various operating conditions. The predictions of the model are verified experimentally through comparison with HDD product reliability test data. View full abstract»

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  • Recent Progress of Patterned Media

    Page(s): 3685 - 3688
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    Recent progress in the development of patterned magnetic recording media is presented, focusing on the results of patterned media fabricated by a self-assembled mask process. Several issues such as fabrication process, flyability, and signal processing have been discussed so far. However, recent progress seems to resolve these problems. A fabrication process using nano-imprint lithography is a possible solution in terms of productivity. Good results for flyability have been reported for discrete track recording media. Certain advantages with respect to signal processing have been reported. Although problems remain to be resolved, patterned media is expected to be commercialized following the introduction of the discrete track media, as a high density perpendicular magnetic recording media. View full abstract»

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  • Write Fault Protection Against Shock Disturbance in Hard Disk Drives Without a Shock Sensor

    Page(s): 3689 - 3693
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (251 KB) |  | HTML iconHTML  

    Write fault protection performance determines the data integrity performance in hard disk drives (HDDs). It is also a critical factor in projection of new HDD products to determine the adequate servo sector number. For HDDs with a shock sensor, the write fault protection performance is rather uniform with respect to different shock disturbance. However, this is not the case when shock sensors are not available and only off-track thresholds are used to detect external shock loads. The write fault protection performance may be dependent on many factors, such as shock form and amplitude, the timing of the shock, the sampling frequency, etc. This paper studied the relationship between the write fault protection performance and shock disturbance in HDDs without shock sensors. Simulations showed that when the shock timing is random, the write fault protection performance is inversely proportional to the shock amplitude. View full abstract»

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  • Lubricant Dynamics in the Sub-Nanometer Clearance Regime

    Page(s): 3694 - 3698
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1165 KB) |  | HTML iconHTML  

    This paper reviews the present state of understanding of lubricant-slider interactions in a rigid disk drive. As slider flying heights are rapidly approaching the intrinsic limit of a disk topography (1-3 nm), it has become apparent that disk-slider clearance of less than a nanometer can be achieved, at least on a laboratory setup. We will discuss the implication of such low spacing on the lubricant film behavior, and provide general physical arguments that attempt to highlight lubricant attributes that are relevant under those clearance conditions. View full abstract»

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  • Direct Visualization of Molecularly Thin Lubricant Films Using Low-Coherence Phase-Shifting Interferometry

    Page(s): 3699 - 3704
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1510 KB) |  | HTML iconHTML  

    We have developed a method utilizing low-coherence phase-shifting interferometry (LCPSI) to directly visualize molecularly thin lubricant films coated on diamond-like carbon (DLC) surfaces. The measurement accuracy is guaranteed by the use of a low-coherence light source, a feedback-controlled phase-shifting system, and an image subtraction method. By measuring nanometer-thick perfluoropolyether films coated on DLC surfaces, we demonstrated that the LCPSI is capable of providing real-time three-dimensional measurements at a sub-nanometer thickness resolution and a spatial resolution of several micrometers. View full abstract»

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  • Effects of End Groups on the Spreading Characteristics of Molecularly Thin Liquid Lubricant Films in Hard Disk Drives

    Page(s): 3705 - 3709
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (531 KB) |  | HTML iconHTML  

    The spreading characteristics of novel alkanolamine-terminated perfluoropolyether (PFPE) films on carbon surfaces were investigated experimentally by using a scanning micro-ellipsometer. The apparent diffusion coefficients of the novel lubricants were studied in order to evaluate the spreading speed and they were compared with the conventional Z-dol, Z-tetraol, and A20H lubricants. It was found that the mobility of a lubricant is lower when the number of OH end groups is higher. It was also found that the mobility of the alkanolamine-terminated PFPE films was lower than that of conventional lubricants with the same number of OH end groups as that of the alkanolamine-terminated lubricants and that the mobility tendency of the lubricants has a good correlation with their viscosity tendency. In addition, the mobility of ZDPA with a dipropylamine end group (no OH end group) has peculiar characteristics. Its mobility is higher than that of Z-dol when the film thickness of the lubricant exceeds that of one monolayer. However, it is lower than that of Z-dol when the film thickness of the lubricant is less than that of one monolayer. This may be due to the unique interaction between the ZDPA amine group and the carbon overcoat. View full abstract»

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  • Lubricant Migration Simulations on the Flying Head Slider Air-Bearing Surface in a Hard Disk Drive

    Page(s): 3710 - 3715
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2579 KB) |  | HTML iconHTML  

    In this paper, we numerically study the lubricant migration on a flying slider air-bearing surface in a hard disk drive. The lubricant dynamics is based on a continuum thin film lubrication theory with inter-molecular forces and a precursor film model. It includes air-bearing pressure, air-bearing shear stress, the Laplace pressure, the disjoining pressure, and the shear stress caused by the surface free energy gradient. Using this model we investigate the lubricant migration behavior on a modern negative pressure type slider surface. We also reveal the correlation between the lubricant migration behavior and the air-bearing shear stress. We further perform the lubricant migration analysis for various different slider designs, radii, and skew angles. View full abstract»

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  • Vibration of 1.8-in Hard Disk Drive Spindle Motors at Various Ambient Temperatures

    Page(s): 3716 - 3720
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (737 KB) |  | HTML iconHTML  

    In this paper, vibration of 1.8-in hard disk drive (HDD) spindle motors is studied experimentally and theoretically. In the experimental study, vibration of 1.8-in HDD motors is measured at 5degC, 25degC, and 70degC in a thermal chamber. Experimental results reveal two important phenomena. First, vibration of 1.8-in HDD spindle motors is dominated by a (0,0) unbalanced mode that has a significant bending deformation of the base plate. Second, the natural frequency of the (0,0) unbalanced mode and the static gain of the frequency response function change significantly as the ambient temperature varies. To explain these experimental observations, we apply a mathematical model developed at the University of Washington to analyze the vibration of the 1.8-in HDD spindle motors. The analysis shows that (0,0) unbalanced mode shifts its natural frequency because membrane stresses are developed in the base plate during temperature changes as a result of a significant mismatch of coefficients of thermal expansion between the base plate and the fixture. Moreover, the change of the static gain results from reduction of fluid-dynamic bearing coefficients as the temperature varies. View full abstract»

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  • Design of Hydrodynamic Bearing for Miniature Hard Disk Drives

    Page(s): 3721 - 3726
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1098 KB) |  | HTML iconHTML  

    This paper has two specific goals to achieve. The first goal is to address major challenges encountered in design and development of miniature hydrodynamic bearings for small form factor hard disk drive spindle motors. These challenges include extremely small thickness of the spindle motors, mass productivity of tiny bearing parts, and bearing reliability and performance in relation to changes in atmospheric pressure. To overcome these challenges, we have developed a prototype hydrodynamic bearing that is resistant to environmental changes, free from oil film disruption, and tolerant of variations in processing precision. The prototype hydrodynamic bearing has two special features: an oil circulation function and a gas/liquid separation function. The oil circulation function is achieved by using asymmetric hydrodynamic grooves together with circulation passages. The gas/liquid separation function is achieved by using tapered capillary seals in the circulation passages. As a result of these two special features, the prototype hydrodynamic bearing can successfully expel air bubbles out of the bearing, thus enhancing the performance and reliability of the hydrodynamic bearing. The second goal is to evaluate the prototype hydrodynamic bearing in a miniature spindle motor for small form factor hard disk drives. Two specific bearing designs are evaluated. The first bearing design is a pushing type that generates no low-pressure area. However, the flow rate increases at high temperature. The second design is just the opposite. It is a pulling type design that generates a low-pressure area. But the flow rate is constant and is independent of temperature changes. To accommodate manufacturing tolerances, a parametric study is conducted to identify the effects of manufacturing tolerance on bearing performance. View full abstract»

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  • A Comparative Study of Turning and Stationary Groove Journal Bearings for HDD Spindle Motors Under Transient Contact Conditions

    Page(s): 3727 - 3733
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    This paper compares the turning and stationary groove configurations of oil lubricated journal bearings used in hard disk drive (HDD) spindle motors under transient contact conditions, such as at startup and shutdown. With rapidly expanding applications for HDDs, spindle motors are required to have lower friction and wear while driving more disks, and be downsized at the same time. It has been known for some time that the turning groove bearing outperforms the stationary groove bearing with regard to friction torque in steady-state operations. However, the friction and wear of the two configurations under the transient contact conditions are still not well understood. To clarify this, we used a model previously proposed and validated experimentally to determine the motion of the turning member in the bearing by simultaneously solving the nonlinear differential equations of motion, the pressure-compliance relationship of elastic-plastic roughness contact, and the average flow Reynolds equation. The different characteristics of the turning and stationary groove configurations are then discussed for both herringbone groove and multi-taper bearings. View full abstract»

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  • Analysis of Three Synchronous Drive Modes for the Starting Performance of Spindle Motors

    Page(s): 3734 - 3737
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (775 KB) |  | HTML iconHTML  

    In sensorless operation of spindle motors in hard disk drives (HDD), open-looped starting is used to spin up the motor from standstill to a speed that is high enough to reliably detect back-electromotive force (back-EMF) generated in the armature windings. Then the back-EMF zero-crossing points (ZCP) will be used to detect speed and position for closed-looped control. This paper studies three open-looped starting modes for spindle motor. Six-step, which is currently used in HDD, twelve-step, and sine wave starting are illustrated and compared. The simulation results show that twelve-step and sine wave starting can obtain much better starting performance for spindle motors. View full abstract»

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  • Finite-Element Shock Analysis of an Operating Hard Disk Drive Considering the Flexibility of a Spinning Disk-Spindle, a Head-Suspension-Actuator, and a Supporting Structure

    Page(s): 3738 - 3743
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1097 KB) |  | HTML iconHTML  

    This paper proposes a finite-element method (FEM) with mode superposition to analyze the shock response of a flexible hard disk drive (HDD) composed of a spinning disk-spindle system with fluid dynamic bearings (FDBs), a head-suspension-actuator with pivot bearings and air bearings, and a base plate with complicated geometry. The proposed method is applied to a 2.5-in HDD. The displacements of the head, spinning disk, and arm are calculated, and they are also measured by experiments. This research shows that the numerical results match well with the experimental ones. It also investigates the head-disk motion due to operational shock. View full abstract»

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  • Design and Analysis of Disk Bump to Improve the Unloading Performance in Hard Disk Drives

    Page(s): 3744 - 3749
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    Most hard disk drives that apply the ramp load/unload technology unload the heads at the outer edge of the disk while the disk is rotating. During the unloading process, slider-disk contacts may occur by lift-off force and rebound of the slider. The main issue of this paper is to prevent the slider-disk contact by rebound, and we apply a disk bump to the unloading process. To do so, first, the ranges of bump dimension are determined. Second, the stability of each bump is checked by dynamic simulation. Finally, unload analyses are performed for stable bump designs. As a result of these analyses, we investigate proper bump design and position for the unloading process. Through this research, we propose the optimal bump design to improve the unloading performance. We can also identify to remove rebound contact by applying a bump on disk to the unloading process. View full abstract»

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  • A Study on Positioning Error Caused by Flow Induced Vibration Using Helium-Filled Hard Disk Drives

    Page(s): 3750 - 3755
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    In this paper, we compare the positioning accuracy of helium- and air-filled drives. We report the PES spectra of the both drives and calculate the mechanical disturbance. The results reveal that almost all disturbances in higher rpm drives are flow induced vibrations and that disturbances in helium-filled drives are dramatically smaller. The experimental positioning error of helium-filled drives is less than half of that of air-filled drives. The static and dynamic fluid computations explaine these experimental results. View full abstract»

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  • Compensation of Dominant Frequency Components of Nonrepeatable Disturbance in Hard Disk Drives

    Page(s): 3756 - 3762
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    This paper is concerned with the nonrepeatable runout (NRRO) compensation problem for hard disk drives. After standard servo control, several visible frequency components remain in the spectrum of nonrepeatable position error signal (NRPES). The dominant ones among these frequency components contribute a lot to the track mis-registration (TMR). In this paper, we propose an adaptive compensation scheme for the time-varying dominant frequency component of NRRO. The frequency of the dominant component is estimated online by the least mean squares (LMS) algorithm within a short time window. Based on the frequency estimate, the basis function algorithm is applied to adaptively identify the time-varying magnitude and phase of the dominant component. With the identified frequency, magnitude, and phase, an estimate of the dominant component is constructed and then canceled by the control signal. This scheme is further extended to compensating for multiple frequency components. The performance of this compensation scheme is demonstrated by simulation on a realistic hard disk drive model. View full abstract»

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  • Model Reduction and Parametric Uncertainty Identification for Robust H2 Control Synthesis for Dual-Stage Hard Disk Drives

    Page(s): 3763 - 3768
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (319 KB) |  | HTML iconHTML  

    This paper presents a systematic, semi-automated method for identifying parameters and parametric uncertainty for a set of dual-stage hard disk drives. A modal analysis technique is selected to extract parameters from a batch of frequency response data. In order to avoid redundancy in modal parameters, two methods are presented to reduce model order. One method combines experimental data to directly extract fewer parameters. The second method uses an optimized model truncation methodology. Finally, convex optimization and singular value decomposition are employed to obtain a minimally conservative, lower-order approximation of uncertain parameters. The result is a reduced-order state space model with parametric uncertainty to be used in robust H2 control synthesis for a track-following hard disk drive servo. View full abstract»

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  • Timing Jitter Modeling and Minimization for a Servo Track Writer

    Page(s): 3769 - 3773
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB) |  | HTML iconHTML  

    During servo track writing (STW), the timing jitter in clocking process can induce significant errors on servo pattern, which is known as phase-in error. In this paper, we measured the timing jitter on our STW setup and modeled the jitter sources in frequency domain. With the timing jitter models, the typical phase-locked loop system is taken as a typical closed-loop control system and loop shaping and control method are used to design the loop filter with objective to minimize the timing jitter. It is shown that timing jitter can be significantly reduced with loop filter designed with the H2 method. View full abstract»

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  • Rejection of Unknown Periodic Disturbances in Magnetic Hard Disk Drives

    Page(s): 3774 - 3778
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (567 KB) |  | HTML iconHTML  

    The magnetic hard disk drive (HDD) has become a cost-effective means to meet the expanding demands for large data storage capacities in portable electronic devices. A particular problem an HDD faces in such applications is periodic disturbances caused by different kinds of external forces. In this paper, an adaptive controller based on an algorithm proposed by Brown has been developed and applied to identify and reject unknown periodic disturbances in a mobile HDD. Numerical simulations and experiments are conducted and superior convergence properties of the proposed method are shown compared with a method taken from the literature called frequency chasing peak filter. It is found that the convergence rate of the proposed method is less susceptive to the error in the initial frequency estimate in the frequency range of interest. The effect of unaddressed frequency components on the convergence and performance of the controller is also discussed. View full abstract»

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  • Servo Signal Quality for Perpendicular Recording in Servo Write Process

    Page(s): 3779 - 3784
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1509 KB) |  | HTML iconHTML  

    In regards to servo-writing with perpendicular recording, we investigated servo-write quality and servo performance, and found that the premagnetization conditions, the magnetic-flux flow mechanism, and head structure strongly affect the servo-write quality. In response to these findings, we clarified that the flux flows through the writer to the reader are one of the root causes of servo-signal deterioration. In addition, we found that the flux amount is related to the magnetization switching ratio (MSR) - a one sided magnetization pole per writer-pole area. On the other hand, the reader can absorb flux even if it is far from the flux source. This means that not only the reader element but also the adjacent structure can absorb flux from the flux source. View full abstract»

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  • Theoretical Study of Self-Excited and Forced Vibrations of Flying Head Slider in Near-Contact Region

    Page(s): 3785 - 3790
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (454 KB) |  | HTML iconHTML  

    After introducing our previous study of bouncing instability of a flying head slider, we numerically investigated slider dynamics in the near-contact region taking the root-mean-square value and frequency roll-off factor of the micro-waviness as parameters by using 2-degrees-of-freedom slider model, random micro-waviness model and lubricated rough-surface-contact characteristics model. We found that the slider exhibits self-excited bouncing vibration with a frequency close to the lower pitch frequency under small microwaviness but tends to exhibit forced vibration with a resonant frequency in the upper pitch mode as the amplitude of microwaviness increases. If the amount of microwaviness and destabilized sources are reduced sufficiently, there is a contact sliding condition without self-excited and forced bouncing vibration. View full abstract»

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  • Designing, Modeling, and Testing Particle Robust Air Bearings for Perpendicular Recording Media

    Page(s): 3791 - 3795
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1501 KB) |  | HTML iconHTML  

    Particle-induced damage on perpendicular recording media can be categorized as physical damage to the media and magnetic erasures with limited physical damage. Component-level tests were developed in order to measure particle robustness of air bearing designs for these two failure modes. A published model for air bearing interactions with a particle was extended to include the full slider surface and allow particles to slide along the slider air bearing features. The model and test results correlate for hard particle scratching. Specific air bearing features and properties can be modified in order to improve dramatically the air bearing particle robustness for hard particle scratches and particle-induced magnetic erasures. 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