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Magnetics, IEEE Transactions on

Issue 1 • Date Jan. 2004

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Displaying Results 1 - 25 of 29
  • [Front cover]

    Page(s): 1
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  • IEEE Transactions on Magnetics Publication Information

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  • Table of contents

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  • Classical model of extrinsic ferromagnetic resonance linewidth in ultrathin films

    Page(s): 2 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB) |  | HTML iconHTML  

    This paper describes a classical version of the two-magnon model of ferromagnetic resonance linewidth in inhomogeneous magnetic thin films. The ferromagnetic resonance line broadening due to inhomogeneity is described in terms of film properties and the statistical properties of the inhomogeneity. Analytical results for the case of ultrathin films in the limit of zero damping are compared with numerical results computed with finite damping. View full abstract»

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  • Element-free Galerkin method for static and quasi-static electromagnetic field computation

    Page(s): 12 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1064 KB) |  | HTML iconHTML  

    Conventional finite-element methods (FEMs) rely on an underlying tessellation to describe the geometry and the basis functions that are used to represent the unknown quantity. Alternatively, however, it is possible to represent both the geometry and basis as a set of points. This alternative scheme has been used extensively in solid mechanics to compute stress and strain distributions. This paper presents an adaptation of the scheme to the analysis of electromagnetic problems in both the static and quasi-static regimes. It validates the proposed model against both analytical solutions and benchmarked FEMs. The paper demonstrates the efficacy of the proposed method by applying it to a range of problems. View full abstract»

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  • Novel modeling and solution approach for repeated finite-element analysis of eddy-current systems

    Page(s): 21 - 28
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    In this paper, we present an efficient modeling and computational scheme for a repeated solution of an eddy-current system with different values of the supply frequency as well as of the permeability and conductivity of the eddy-current region. The scheme is based on a general parametric expression obtained for the finite-element (FE) solution with the supply frequency, permeability, and conductivity as parameters. The algorithm allows for numerically efficient updating of the solution for different values of the parameters through the solution of a much smaller sparse linear system, instead of a repeated solution of the entire FE model. Moreover, if required, the solution can be computed only over a small region of interest, making the scheme ideally suited to many coupled-field problems. As an application, the scheme is applied to a typical bar-plate eddy-current system, excited by nonsinusoidal currents. The time variations of the magnetic field are computed as a superposition of responses computed for a number of harmonics. An a priori estimate for the difference between responses to two harmonics has been obtained, which can be used as a frequency-sensitivity measure to avoid computation of responses to all individual harmonics. The applicability of the approach to general transient excitations and further possible developments are identified. View full abstract»

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  • Three-dimensional integral method for modeling electromagnetic inductive processes

    Page(s): 29 - 36
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    This paper describes a three-dimensional integral method that models electromagnetic phenomena taking place during inductive melting. The method is well suited to inductive systems undergoing sinusoidal excitation at midrange or high frequencies. Under these conditions, only the surfaces of the conductors need to be meshed. The unknowns of the model are current density and scalar electrical potential. Power density, electromagnetic forces, and electrical impedance can easily be derived. Comparisons between numerical results and measurements confirm the accuracy of the model. View full abstract»

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  • Mathematical design of an electromagnetic separation sensor in molten aluminum

    Page(s): 37 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    This paper describes an investigation of an electromagnetic separation approach for separating inclusions in molten aluminum. The separation is effected by a magnetic field generated by a direct current, resulting in a Lorentz force. On the basis of this magnetic separation method, we constructed a sensor probe and rigorously analyzed it from a mathematical point of view. Specifically, we calculated the magnetic field inside the probe and showed that a nonuniform body force density is established throughout the melt volume, resulting in a decrease in probe efficiency. Moreover, we analyzed the rotational motion of the melt under the influence of the spatially dependent body force, and reasoned that this rotational motion also adversely affects the probe performance. To overcome these two drawbacks, we propose a new probe design. The goal of the new design is to increase strength and uniformity of the body force distribution within the aluminum melt. View full abstract»

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  • Mechanical damage detection with magnetic flux leakage tools: modeling the effect of localized residual stresses

    Page(s): 43 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3504 KB) |  | HTML iconHTML  

    We used three-dimensional (3-D) magnetic finite-element analysis (FEA) to simulate the effect of localized residual stresses on magnetic flux leakage (MFL) signals from a steel plate in the absence of a geometrical defect. We derived the local residual stress patterns from finite-element structural modeling of simulated dents. The magnetic FEA model simulates these localized residual stresses by assigning appropriate directional permeability values to the magnetically anisotropic materials. Considering the necessary simplifications required for magnetic FEA modeling, the simulated MFL patterns are in good agreement with the experimentally observed patterns associated with the stresses around a dent. View full abstract»

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  • Analytical method for predicting the air-gap flux of interior-type permanent-magnet machines

    Page(s): 50 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB) |  | HTML iconHTML  

    This paper presents an analytical method to calculate the air-gap magnetic flux of interior-type permanent-magnet (IPM) machines taking into account the assembly gap and saturation in stator and rotor. Special considerations are given to the calculation of leakage flux in the nonlinear magnetic short circuit or the "magnetic bridges." An equivalent magnetic circuit was developed, and a computer-aided graphic analysis program calculated the magnet operating point. The Norton equivalent of flux concentration structures was studied. Agreements have been obtained between the results of the analytical model, finite-element analysis, and test results on prototype motors. View full abstract»

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  • Modeling maglev passenger compartment static magnetic fields from linear Halbach permanent-magnet arrays

    Page(s): 59 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    Passenger compartment magnetic field levels in a low-speed magnetic levitation (maglev) vehicle that uses linear Halbach permanent-magnet arrays for both levitation and propulsion are computed through superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. End effects due to the finite lengths of the arrays lead to fields that decay much less rapidly with distance from the arrays than the near-field exponential decay based on array wavelength, and do not have the strong side/weak side character of the near fields. End effects dominate the maglev passenger compartment fields. Contour plots of computed fields due to the magnet arrays for a specific maglev design show field magnitudes of about 1.5 G at floor level, 0.5 G at seat level, and 0.2 G at head level. View full abstract»

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  • Microfabrication and characteristics of low-power high-performance magnetic thin-film transformers

    Page(s): 65 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    We investigated low-power (1.5-W), solenoid-type magnetic thin-film transformers with a Ni81Fe19 core for a 5-MHz drive dc-dc converter application. We used 2-μm-thick Ni81Fe19 films covered by 20-μm-thick copper coils as the core materials. The transformers fabricated in this study range in size from 3.08 mm × 25.5 mm to 6.15 mm × 12.75 mm. The design of the transformers was optimized by utilizing the conventional equations, a Maxwell three-dimensional field simulator, and parameters obtained from the magnetic properties of NiFe magnetic core materials. The 6.15 mm × 12.75 mm transformers exhibit inductance (L) of 0.83 μH, dc resistance of 2.3 Ω, coupling factor of 0.91, and gain of -1 dB at 5 MHz. These results are comparable to those reported in recent literature for various types of transformers sandwiched by more complex magnetic core materials. The calculated data obtained by using the well-known equation of L and the equivalent circuit agreed well with the high-frequency data for L and gain of the transformers. View full abstract»

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  • Dynamic magnetomechanical behavior of terfenol-D/epoxy 1-3 particulate composites

    Page(s): 71 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    We investigated the dynamic behavior of 1-3 type magnetostrictive particulate composites as a function of both bias field (5-140 kA/m) and frequency (1-100 kHz). The composites consist of approximately 0.5 volume-fraction Terfenol-D particles embedded and magnetically aligned in a passive epoxy matrix. The measured properties include elastic moduli (E3H and E3B), dynamic relative permeability (μr33), dynamic strain coefficient (d33), magnetomechanical coupling coefficient (k33), and the ratio of the dynamic strain coefficient to the dynamic susceptibility (d3333). We observed the dependence of these properties on bias field and explain it here in terms of domain-wall motion followed by saturation near 40 kA/m. The spectra of μr33, d33, and d3333 indicate that the magnetization process is independent of frequency and that the effect of eddy-current losses is insignificant up to 100 kHz. The observations agree with predictions made by classical eddy-current theory and suggest that the composites can be operated at significantly higher frequencies than monolithic Terfenol-D. View full abstract»

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  • Applied time-domain network characterization and simulation

    Page(s): 78 - 84
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    Characterizations or models of electrical networks assist designers in predicting how a network will perform in a proposed system without physically constructing the complete system. This allows engineers to quickly test, by simulation, various options and thereby reduce design costs and schedules. For linear networks, characterizations may be obtained from measurements made at the network ports. These models are commonly developed in the frequency domain; such models can be applied directly in frequency-domain simulation and indirectly in time-domain simulation. Alternatively, measurements taken at the ports can also be used to develop time-domain models that are directly applicable for time-domain simulation. This alternate approach has the advantages of avoiding sometimes-difficult transformations and requiring only time-domain instrumentation. View full abstract»

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  • Shaped time-optimal feedback control for disk-drive systems with back-electromotive force

    Page(s): 85 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    In this paper, we describe the design of closed-loop control laws for disk-drive systems that account for back-electromotive force (back-EMF) by using a phase-plane approach. The time-optimal control law for a rigid body is shaped by using input shaping ideas to address the flexible mode, and then the altered rigid body phase-plane trajectories resulting from this shaping are calculated and used to determine a closed-loop controller. Extensions are made to account for damping and slew rate limits. Simulation results show that this control approach leads to near-time-optimal performance without unwanted residual vibrations, good robustness to modeling errors, and faster time response than the previously developed extended proximate time-optimal servomechanism (XPTOS) control, especially when the flexible dynamics are dominant. View full abstract»

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  • Response function study of a new kind of multilayer-coated tip for magnetic force microscopy

    Page(s): 97 - 100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1080 KB) |  | HTML iconHTML  

    We studied the spatial frequency response of a multilayer-coated tip for magnetic force microscopy both theoretically and experimentally. The tip coating is a multilayer structure, with two ferromagnetic layers coupled in antiparallel via an ultrathin nonmagnetic layer. We simulated the magnetic response of this kind of tip for longitudinal magnetic transitions. The results showed that the multilayer tip has a higher resolution than a single-layer tip. View full abstract»

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  • Angular sensor using tunneling magnetoresistive junctions with an artificial antiferromagnet reference electrode and improved thermal stability

    Page(s): 101 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    Magnetic tunneling junctions (MTJs) are fabricated using CoFe-Ru-CoFe artificial antiferromagnet (AAF) sandwiches as a hard-magnetic reference layer and plasma-oxidized aluminum as a tunnel barrier. Tailoring the magnetic properties of the artificial antiferromagnet reference layer allows an on-chip magnetization (initialization) of individual junctions, which makes it possible to build monolithic bridges in a Wheatstone arrangement without multiple mask process steps or on-chip heating elements. The functionality of an angular field sensor based on this concept is demonstrated in detail. The thermal stability of such a sensor is investigated and the limitations of the concept are discussed. View full abstract»

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  • Theoretical limit to domain position detection magnetic amplifying magnetooptical system

    Page(s): 105 - 111
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    We developed a model that was used to evaluate the performance of a domain position detection magnetic amplifying magnetooptical system (DPD-MAMMOS). Through the use of the model, we explain the operation of DPD-MAMMOS and demonstrate its advantages. Next, we evaluated the performance of DPD-MAMMOS under the influences of position noise from a theoretical point of view. From this analysis, we estimate that a MAMMOS system will need to attain 30 nm or less of position noise to show a density advantage when used with DPD-MAMMOS. View full abstract»

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  • Readback responses for complex recording media configurations

    Page(s): 112 - 128
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    This paper describes a relatively simple approach to calculating the frequency response for a two-dimensional (2-D) magnetic recording system with a medium that can include an arbitrary number of layers. Each layer may have an arbitrary magnetization direction, anisotropic permeability, and exchange coupling. The approach relies on an initial transformation into the spatial frequency domain and then the use of transmission matrices to relate the fields in the different layers. The approach is general in that it provides a method for finding the field configuration for any set of 2-D magnetic sources embedded in a layered magnetic medium with a linear B--H relationship. Here, we focus on calculating the readback response for a variety of longitudinal and perpendicular recording configurations. Since the permeability may have any wavelength dependence, we can easily include the effect of exchange coupling in the underlayer. View full abstract»

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  • Correlation of DC noise and transition noise in magnetic recording

    Page(s): 129 - 136
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1152 KB) |  | HTML iconHTML  

    We studied a correlation between the local transition noise and the dc noise at the same location of magnetic medium. We describe experimental techniques for local dc noise and transition noise analysis and demonstrate that the local fluctuations of the dc saturated magnetization become enhanced when a transition is written at this location. This enhanced local dc noise is a very significant contributor to the total noise power of a transition. View full abstract»

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  • Thermal Williams-Comstock model for predicting transition lengths in a heat-assisted magnetic recording system

    Page(s): 137 - 147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB) |  | HTML iconHTML  

    A thermal Williams-Comstock recording model was developed to predict the transition length in a longitudinal heat-assisted magnetic recording system. In this paper, we compare the results from the model to experimentally determined transition lengths from a dual-sided heat-assisted magnetic recording spin stand. We found both experimentally and theoretically that there exists an optimal alignment between the thermal profile and the magnetic head, which minimizes the transition length. By properly optimizing the write current and laser power, it was possible to record transitions shorter then those attainable with conventional longitudinal recording. View full abstract»

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  • Approximate three-dimensional head fields for perpendicular magnetic recording

    Page(s): 148 - 156
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1152 KB) |  | HTML iconHTML  

    This paper proposes a method for obtaining approximate, but very accurate, three-dimensional (3-D) head fields for perpendicular magnetic recording heads. The method uses an assumed form for the scalar magnetic potential variation between a pole or shield and the underlayer to give the potential in the head/shields-face plane. It then uses this approximate air-bearing surface potential to find the potential or field components at any other position of interest. The approach is illustrated here by applying it to a symmetric double-shielded single-pole head with an underlayer and with side shields. View full abstract»

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  • Effect of pole-tip geometry on the flux rise time of write heads

    Page(s): 157 - 160
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB) |  | HTML iconHTML  

    With magnetic recording data transfer rates now in the gigabit-per-second regime, understanding and controlling all of the major write transducer characteristics governing magnetic flux rise time has become imperative. In this paper, we study dependence of the flux rise time on the front-end pole-tip geometry. We examined a set of recording heads differing only in pole-tip shape; the yoke length and width, number of coil turns, and pitch are the same for all designs. We measured the flux rise time by laser-based time-resolved scanning Kerr microscopy and observed that the front-end pole-tip geometry has a strong effect on flux rise time. View full abstract»

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  • Frequency-modulation-type MI sensor using amorphous wire and CMOS inverter multivibrator

    Page(s): 161 - 163
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    A new frequency-modulation-type magnetoimpedance (MI) sensor using amorphous wire and a complimentary metal-oxide-semiconductor (CMOS) multivibrator is presented. The normal switching mode (mode I) with the alternative saturation and off states in the p-MOSFET and n-MOSFET maintains a stable multivibrator oscillation and simultaneous CMOS unsaturation state mode (mode II) generates a sensitive MI effect. A 50%/Oe change in the oscillation frequency versus external dc magnetic field was obtained. A linear sensor characteristic is obtained using a negative feedback through a frequency-voltage converter. View full abstract»

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  • Enhancement of grain isolation by interlayer diffusion in AFC media with CrMo spacer layer

    Page(s): 164 - 166
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1336 KB) |  | HTML iconHTML  

    It was found that a reduction in Mrt can be obtained in the new antiferromagnetically coupled (AFC) medium with a CrMo spacer layer due to antiferromagnetic (AF) coupling, which is similar to the conventional AFC medium with a Ru spacer layer. From the results of ΔM and magnetic force microscopy (MFM), it was found that the intergranular exchange coupling decreases when CrMo is used as a spacer layer. Micromagnetic simulations of ΔM and MFM analyses gave consistent results with experiment, i.e., 1) AFC media with higher intergranular exchange coupling constant have larger magnetic cluster and higher ΔM peak and 2) the media with higher AF coupling constant have smaller magnetic cluster and smaller ΔM. In this paper, we propose that the media noise of the AFC media with a CrMo spacer layer may be improved by a reduction in the magnetic cluster size, due to the decrease of the intergranular exchange coupling between magnetic grains. 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