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Magnetics, IEEE Transactions on

Issue 12 • Date Dec. 2005

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Displaying Results 1 - 19 of 19
  • [Front cover]

    Page(s): c1
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  • IEEE Transactions on Magnetics publication information

    Page(s): c2
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  • Table of contents

    Page(s): 4373
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  • First principles calculations of FePt, CoPt, Co3Pt, and Fe3Pt alloys

    Page(s): 4374 - 4379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    First principles calculations based upon density functional theory have been used to investigate the magnetic properties of various Fe-Pt and Co-Pt alloys. At the 50:50 composition, the technologically important L10 alloys CoPt and FePt show large magnetocrystalline anisotropies consistent with the natural layering of the crystal structure. Calculated values for the magnetocrystalline anisotropy and magnetizations are found to be in close agreement with measured values. Since the L10 phase forms over a range of compositions, the influence of composition on magnetic properties has also been examined. A simple expression, derived from the Ne´el model, relates the anisotropy to the composition, or degree of disorder in the structure, and is found to be of value for understanding anisotropy in imperfect structures. At greater Fe of Co compositions there are several interesting crystal structures including the metastable pmm2 phase that is composed of alternating pure and mixed planes. Again, fairly large anisotropies are seen as a consequence of layering and symmetry. Growing Fe3Pt pmm2 films seems less promising than Co3Pt pmm2 films given the larger energy difference between the pmm2 and cubic L12 phases. View full abstract»

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  • Electroplated hard magnetic material and its application in microelectromechanical systems

    Page(s): 4380 - 4383
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1160 KB) |  | HTML iconHTML  

    We describe the preparation of CoNiMnP-based permanent-magnet material using several sulfate and chloride solutions. We studied eight samples, and all the samples show vertical magnetic anisotropy. Sample8, which was electroplated from a low-concentration chloride solution and under external magnetic field, demonstrates the best magnetic properties with coercivity 2632 Oe, remanence 0.20 T, and maximum magnetic energy 10.185 kJ/m3. An array structure can avoid the stress between the electroplated layer and the seed layer. The electroplated Co0.8Ni0.1174Mn0.0062P0.0762 permanent magnet has potential for bidirectional actuators in micro-electromechanical systems. View full abstract»

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  • Magnetic properties of biosynthesized magnetite nanoparticles

    Page(s): 4384 - 4389
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    Magnetic nanoparticles, which are unique because of both structural and functional elements, have various novel applications. The popularity and practicality of nanoparticle materials create a need for a synthesis method that produces quality particles in sizable quantities. This paper describes such a method, one that uses bacterial synthesis to create nanoparticles of magnetite. The thermophilic bacterial strain Thermoanaerobacter ethanolicus TOR-39 was incubated under anaerobic conditions at 65°C for two weeks in aqueous solution containing Fe ions from a magnetite precursor (akaganeite). Magnetite particles formed outside of bacterial cells. We verified particle size and morphology by using dynamic light scattering, X-ray diffraction, and transmission electron microscopy. Average crystallite size was 45 nm. We characterized the magnetic properties by using a superconducting quantum interference device magnetometer; a saturation magnetization of 77 emu/g was observed at 5 K. These results are comparable to those for chemically synthesized magnetite nanoparticles. View full abstract»

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  • Magnetization reversal simulation of diamond-shaped NiFe nanofilm elements

    Page(s): 4390 - 4393
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    We have studied magnetization reversal behaviors of diamond-shaped NiFe nanofilm elements with different length-to-width ratios (LWRs) between long and short diagonals by micromagnetic simulation. The results show that the reversal process of the diamond-shaped element strongly depends on the LWR. If the LWR is smaller than 2, the reversal starts at the element edge, but it starts from the center of the element with larger LWR. With a bias field and when the LWR is larger than 2, all the elements experience a similar reversal process, which is simple and unique. In addition, the switching field becomes stable and nearly constant. These results suggest that the diamond-shaped NiFe nanofilm element can be potentially used in magnetic random access memory. View full abstract»

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  • Low-noise magnetic force microscopy with high resolution by tip cooling

    Page(s): 4394 - 4396
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    Low-noise magnetic force microscopy (MFM) was realized by using a conventional high-vacuum MFM with homemade tip-cooling equipment. The noise level of the MFM at a tip temperature of 130 K was estimated at μN/m order. High spatial resolution of 10 nm was obtained for observing high-density recording media with recording density of 1000 kfci. The improvement of resolution by tip cooling was a result of the reduction of thermodynamic noise of a cantilever and the effective reduction of tip-sample distance due to the magnetic hardening of a tip. View full abstract»

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  • Fabrication of ultralow-profile micromachined inductor with magnetic core material

    Page(s): 4397 - 4400
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    We have fabricated a microinductor with an ultralow profile by a microelectromechanical systems (MEMS) technique. The fabrication process uses UV-LIGA, dry etching, fine polishing, and electroplating to achieve high performance. The dimensions of the inductor are 1500 μm×900 μm×100 μm. It has 41 turns, with coil width of 20 μm, space of 20 μm, and a high aspect ratio of 5 : 1. The inductance is 0.424 μH and the quality factor (Q factor) is about 1.7 at a frequency of 1 MHz. The stray capacitance is approximately zero over the frequency range measured. View full abstract»

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  • Adaptive wavelet neural network control for linear synchronous motor servo drive

    Page(s): 4401 - 4412
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB) |  | HTML iconHTML  

    We propose an adaptive wavelet neural network (AWNN) control system to control the position of the mover of a permanent-magnet linear synchronous motor (PMLSM) servo drive system to track periodic reference trajectories. The AWNN control system, uses a wavelet neural network (WNN) with accurate approximation capability to represent the unknown dynamics of the PMLSM. It also uses a robust term to confront the inevitable approximation errors due to the finite number of wavelet basis functions and to disturbances, including the friction force. An adaptive learning algorithm that learns the parameters of weight, dilation, and translation of the WNN on line is based on the Lyapunov stability theorem. To relax the requirement for the bound of uncertainty in the robust term, which comprises a minimum approximation error, optimal parameter vectors, higher order terms in Taylor series, and friction force, an adaptive bound estimation law is used; in the estimation, a simple adaptive algorithm estimates the bound of uncertainty. Our simulated and experimental results for periodic reference trajectories show that the dynamic behavior of the proposed control system is robust with regard to uncertainties. An adaptive wavelet neural network (AWNN) control system is proposed to control the position of the mover of a permanent magnet linear synchronous motor (PMLSM) servo drive system to track periodic reference trajectories in this study. In the proposed AWNN control system, a WNN with accurate approximation capability is employed to approximate the unknown dynamics of the PMLSM, and a robust term is proposed to confront the inevitable approximation errors due to finite number of wavelet basis functions and disturbances including the friction force. The adaptive learning algorithm that can learn the parameters of weight, dilation and translation of the WNN on line is derived using Lyapunov stability theorem. Moreover, to relax the requirement for the bound of uncertainty in robust term, which comprises a minimum approximation error, optimal parameter vectors, higher-order terms in Taylor series and friction force, an adaptive bound estimation law is investigated where a simple adaptive algorithm is utilized to estimate the bound of uncertainty. Furthermore, the simu- lated and experimental results due to periodic reference trajectories show that the dynamic behaviors of the proposed control systems are robust with regard to uncertainties. View full abstract»

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  • A novel switched reluctance motor with C-core stators

    Page(s): 4413 - 4420
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB) |  | HTML iconHTML  

    This paper presents a novel switched reluctance motor (SRM) design in which the stator is simply formed from C-cores. Unlike conventional SRMs, the windings of the new motor can be individually wound into the stator cores without complex winding equipment. Because of the inherent axial field distribution, this type of SRM requires a three-dimensional (3-D) finite-element analysis (FEA) model for detailed flux analysis. This paper proposes an approximated two-dimensional FEA model to speed up computational time. In addition, since the proper current that ensures operation in the saturated region (to maximize torque and efficiency) is often hard to determine systemically, the paper proposes a simple method to determine the optimum operating current so that one can easily decide the rated current and also obtain the maximum motor efficiency. Finally, the paper compares some characteristics of a traditional SRM with those of the proposed SRM. The comparison shows that the proposed SRM performs well in terms of torque and efficiency, and provides a higher degree of flexibility in winding design. View full abstract»

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  • Determination of tooth cogging force in a hard-disk brushless DC motor

    Page(s): 4421 - 4426
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    The paper proposes a new method to determine the tooth cogging force in a brushless DC (BLDC) motor which is used in a hard-disk application. This force might be a source of tooth vibrations and motor noise. In the new method, the permanent-magnet (PM) poles are substituted with their equivalent currents. Then, the conformal mapping (CM) method is applied to determine the PM magnetic field. Finally, the cogging force is determined by integrating the magnetic field pressure over the tooth surface. The paper also analyzes the harmonic content of both radial and tangential force components. View full abstract»

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  • Noise predictive belief propagation

    Page(s): 4427 - 4434
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    We introduce iterative noise whitening for belief-propagation-based channel detectors over intersymbol interference channels with correlated additive noise. In particular, we consider longitudinal magnetic recording systems. The proposed "noise predictive belief propagation" (NPBP) detector iteratively whitens the noise samples by modifying the edge probability computation. NPBP detectors based on finite impulse response and infinite impulse response prediction filters are developed. In addition, we introduce a novel prediction filter optimization method leading to a better noise whitening performance. Simulation results for both coded and uncoded systems show that significant improvements can be obtained. View full abstract»

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  • Improvements in SOVA-based decoding for turbo-coded storage channels

    Page(s): 4435 - 4442
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (SOVA). We first identify the reason behind these exaggerated values and then propose a simple remedy for it. We argue that what leads to this optimistic extrinsic information is the inherent strong correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA). Our proposed remedy is based on mathematical analysis, and it involves using two attenuators, one applied to the immediate output of the SOVA and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). We examine the modified SOVA (MSOVA) on idealized partial response (PR) channels and the Lorentzian channel equalized to a PR target. We consider both parallel concatenated codes (PCCs) and serial concatenated codes (SCCs). We show that the MSOVA provides substantial performance improvements over both channels. For example, it provides improvements of about 0.8 to 1.6 dB at Pb=10-5. Finally, we note that the proposed modifications, while they provide considerable performance improvements, introduce only two additional multipliers to the complexity of the SOVA algorithm, which is remarkable. View full abstract»

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  • Self-heating in thin-film magnetic recording heads due to write currents

    Page(s): 4443 - 4448
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    Self-heating due to write currents is a critical concern in thin-film magnetic recording heads; the reliability of the head-media interface and magnetoresistive sensors can be degraded by excessive temperature rise during writing operations. A combined experimental and theoretical study shows that the magnetic saturation of yoke structures and the heat transfer across the air bearing strongly influence the magnitude and spatial distribution of the temperature rise. This paper describes three-dimensional numerical heat transfer simulations that can accurately model self-heating as a function of the amplitude and frequency of write current pulses. View full abstract»

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  • Effect of pole-tip size on perpendicular recording head remanence

    Page(s): 4449 - 4453
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    To aid understanding the physical mechanisms responsible for the perpendicular write head remanent field and thereby improve the write head design, we studied the remanence of single-pole perpendicular recording heads with trailing shield by using a contact scanning recording tester. We used two different pole-tip size heads in the study. We found that the remanence areas of the heads tested usually locate at the trailing edge corners of the pole tip. We also found that the remanence areas of both types of heads are also the head field easy-rising areas when the heads are driven by low write currents. Additionally, the current level that leads to remanence is the same for both types of heads. However, the remanence of the small pole-tip heads can be demagnetized by a much lower amplitude reverse current than that of the large pole-tip heads. View full abstract»

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  • Voltage pulsing for localized clearance measurement

    Page(s): 4454 - 4456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    Mechanical clearance is a critical parameter of the head/disk interface (HDI) for sliders flying in close proximity in hard disk drives. It depends on a variety of HDI parameters, such as the air-bearing design, disk roughness, and the disk lubricant. An experimental setup was developed to determine the mechanical clearance locally at any location on the disk. Voltage pulsing is used to add an additional force component to the complex HDI equilibrium. The applied force is attractive in character and therefore reduces the mechanical spacing between the slider and the disk. If the magnitude of the applied voltage is changed, a slight contact between the slider and the disk can be realized. Simultaneous measurement of the induced slider displacement using a laser vibrometer allows the quantification of the mechanical clearance. The effect of disk roughness and microwaviness on the mechanical clearance is investigated. View full abstract»

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  • 2005 Index

    Page(s): 4457 - 4584
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  • IEEE Magnetics Society Information

    Page(s): c3
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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