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Magnetics, IEEE Transactions on

Issue 12 • Date Dec. 2006

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Displaying Results 1 - 25 of 25
  • [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): 3793 - 3794
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  • IEEE Magnetics Society Distinguished Lecturers for 2007

    Page(s): 3795 - 3798
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  • Sintering Effect of Annealed FePt Nanocrystal Films Observed by Magnetic Force Microscopy

    Page(s): 3799 - 3802
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3473 KB) |  | HTML iconHTML  

    Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500degC. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605degC-630degC. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing View full abstract»

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  • Computer-Aided Performance Evaluation of a Multichannel Transcranial Magnetic Stimulation System

    Page(s): 3803 - 3808
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3660 KB) |  | HTML iconHTML  

    We have evaluated a multichannel transcranial magnetic stimulation (TMS) system using realistic simulations based on the boundary element method (BEM). We investigated various configurations and types of stimulation coils by means of quantitative measures such as targeting accuracy and field concentration. The simulation studies applied to four different head-brain models suggest improved coil types yielding enhanced targeting accuracy and concentrated evoked electric field distribution View full abstract»

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  • Generalized Constructive Model of Hysteresis

    Page(s): 3809 - 3817
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    We describe a generalized constructive model of rate independent scalar hysteresis. It consists of an algorithm that uses a set of experimental hysteresis minor loop vertical chords. The introduced model requires new, less constraining properties than the congruency and equal vertical chords properties required by the classical and the generalized Preisach models. Our model allows for fitting transition curves of order greater than two, despite its simple mathematical notation. Further, we describe interesting performance of the model in numerical evaluation and inversion View full abstract»

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  • A Method for Optimal Identification of a Stop Model With Input-Dependent Shape Function

    Page(s): 3818 - 3824
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (482 KB) |  | HTML iconHTML  

    An optimal identification method is developed for an efficient hysteresis model: a stop model having an input-dependent shape function. To simplify the identification procedure, the input-dependent shape function is given by the product of a weighting function and an input-independent shape function. The optimal weighting function is determined using the least-squares method. To obtain an optimal weighting function, two methods are proposed: one uses the property of equal vertical chords, the other is based on a symmetry condition. Both methods effectively improve the representation accuracy of B--H loops of silicon steel sheets using the stop model. The representation capability of the stop model is compared with that of the play model View full abstract»

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  • Constriction and Corner Permeances for Finite Domains

    Page(s): 3825 - 3831
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    The known formulas for two-dimensional "corner" and "constriction" permeances, which were derived by using conformal mappings for infinite domains, can be applied only for large enough domains. In this paper, we analytically solve the problem for finite domains and propose new exact and approximate formulas. We show that, for finite domains, the corner and constriction permeances can be much smaller than for infinite dimensions, and we determine the limits of applicability of simple exact formulas. This offers the possibility to make more accurate analytical calculations of magnetic devices and better evaluate acting magnetic forces View full abstract»

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  • A Three-Dimensional Semi-Analytical Study of the Magnetic Field Excitation in a Radial Surface Permanent-Magnet Synchronous Motor

    Page(s): 3832 - 3841
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    This paper presents a three-dimensional analytic study of some radial surface permanent-magnet machines, these machines being slotless and without polar pieces. The permanent magnets are represented by Coulomb's model. The sources are developed into a Fourier series. The method of separation of variables in Laplace's equations is used to calculate the magnetic scalar potentials, which lead directly to the flux density. The study yielded a new three-dimensional analytical formulation of such synchronous machines. The results are constituted by analytical expressions of magnetic scalar potentials, the flux densities, and some of their graphs View full abstract»

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  • Simplified Design Methodology for a Slotless Brushless DC Motor

    Page(s): 3842 - 3846
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (354 KB) |  | HTML iconHTML  

    The paper presents a simplified analytical method to design a small two-pole slotless brushless dc motor. Using only a few approximations, the motor analytical model is formulated to generate a system of equations. The system can be solved analytically, producing a motor design for given specifications. The method is used to design a motor with the specifications 150 W, 10 000 rpm, and 18 V View full abstract»

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  • Optimal Design of Multi-Airgap Electrical Machines: An Unknown Size Mixed-Constrained Global Optimization Formulation

    Page(s): 3847 - 3853
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    This paper solves, in a rational way, more sophisticated electrical machine design problems by extending the work done by Fitan et al. It addresses the special case of multi-airgap cylindrical concentric machines. The solution requires a reformulation of the inverse problem associated with the design of electrical machines. Thus, a new mixed-constrained global optimization problem has to be solved. From a mathematical point of view, a major difficulty is that the number of variables and constraints varies during the resolution, depending on the number of considered airgaps. Moreover, this involves extensions of analytical models used for permanent-magnet machines. The paper uses numerical tests for concentric rotor machines with one, two, and three (in one case) mechanical airgaps to validate this methodology of design View full abstract»

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  • Active-Passive Shielding for MRI Acoustic Noise Reduction: Network Analysis

    Page(s): 3854 - 3860
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    We have modeled the effect of passive copper shielding applied to the outside of an actively shielded, axisymmetric z-gradient coil assembly, with the aim of substantially reducing induced eddy currents in the cryostat inner bore that create acoustic noise. For the purpose of calculation, the cylindrical cryostat inner bore and the passive copper shielding are coaxial and are imagined to be sliced into thin ring sections. Each ring section has a finite thickness and is further divided into several concentric layers. The thin cylindrical sections become elements in an electrical network that includes the actively shielded gradient coil. We calculate eddy currents both for single frequency excitations and for time-dependent excitations by modeling a series of trapezoidal pulses. Our results take into account time dependence, diffusion of eddy currents among cylindrical sections and skin depth effects. Two configurations are analyzed. The first is a thin copper layer wrapped around the outer diameter of the gradient assembly, and the second extends the copper over the ends of the gradient assembly. A 2-mm-thick copper layer around the gradient assembly reduces power deposited in the cryostat inner bore by 13.5 dB for a 1 kHz gradient excitation. Extending the passive shield, for the same 2 mm thickness, to cover the ends of the gradient reduces cryostat inner bore power deposition, by 26.7 dB for the same frequency View full abstract»

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  • Coil and Magnet Design for Nuclear Magnetic Resonance in Inhomogeneous Field

    Page(s): 3861 - 3867
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1863 KB) |  | HTML iconHTML  

    High-resolution nuclear magnetic resonance (NMR) spectrometry is possible in nonhomogeneous magnetic fields-such as those in portable equipment-if the static and the radio-frequency (RF) magnetic fields are perpendicular and correlated in the measurement volume. From the easy-axis rotation theorem and the Amperian currents model, it is possible to exactly match two magnetic fields in two-dimensional systems. We derive a basic probe element that fulfills these conditions. Then we present a portable NMR probe design. The static and RF magnetic fields of the probe are matched on a large volume View full abstract»

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  • A Fast and Accurate Method for Measuring Adjacent-Track Erasure

    Page(s): 3868 - 3873
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (779 KB) |  | HTML iconHTML  

    This paper reports on a novel spin-stand method to measure adjacent-track erasure (ATE). The method divides a track into multiple sectors and makes use of the built-in servo system to ensure a highly accurate, amplitude-based measurement. By arranging subtracks uniformly across the range of interest around a center track, a quasi-continuous, detailed ATE profile can be obtained. We discuss the various features of this profile and how they depend on such parameters as skew angle, write current, frequency, and flying height. We then compare the ATE performance of state-of-the-art longitudinal and perpendicular recording components under realistic test conditions, such as may be used for a 250 GB/platter 95 mm desktop drive. We show that the perpendicular head and media compare favorably to longitudinal ones even though the track width is much narrower View full abstract»

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  • Side-Track Erasure Processes in Perpendicular Recording

    Page(s): 3874 - 3879
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    In perpendicular recording, substantial erasure of the stored data patterns can occur during the writing process. Among all those erasure processes, side-track erasure (STE) is one of the critical issues in drive head/media integration. Unlike the adjacent track erasure (ATE) process, the locations of the STE affected areas are often many tens of tracks away from the central writing track location. In this work, we report on an experimental investigation and quantification of the general attributes and the origins of the STE processes in various situations. Particularly, we thoroughly characterize some distinctive signatures and behaviors of STE processes by employing both the amplitude- and bit-error-rate-based STE measurement methods in combination with a novel magnetic force microscope characterization technique View full abstract»

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  • Effects of the Disproportionation Stage of the HDDR Process on Magnetic Properties and Microstructure of Pr $_13$Fe $_80$B $_7$ Alloys

    Page(s): 3880 - 3882
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    Effects of the heat treatment conditions of the disproportionation stage on magnetic properties of hydrogenation disproportionation desorption recombination (HDDR) Pr13Fe80B7 material are investigated. The results show that the HDDR Pr13Fe80B7 material disproportionated by heating from room temperature under hydrogen (C-HD), has high coercivities and low remanences while that heated up to 800degC under vacuum, and then disproprotionated by exposing to hydrogen (V-HD), show high remanences with low coercivities. Further investigations show that this difference of magnetic properties of HDDR Pr13Fe80 B7 materials, which is caused by the C-HD and V-HD treatment, might be related to the disproportionation at low temperature (650degC) in the C-HD treatment. At the same time, it is also found that the microstructure of the Pr13Fe80B7 alloys disproportionated by C-HD treatment is mainly spherical while that of the alloys disproportionated by V-HD treatment is mainly rod-like View full abstract»

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  • Pt Content Dependence of Magnetic Properties of CoPt/Ru Patterned Films

    Page(s): 3883 - 3885
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    The magnetic properties of dot arrays made of CoPt/Ru perpendicular films (20 nm thickness) were examined as a function of Pt content. The CoPt dot arrays with a dot size D of 140 nm showed a single domain state, after removal of the applied field equal to Hr. Hr decreased from 5.2 kOe to 3.0 kOe as the Pt content decreased from 20 at% to 14 at%. The angular dependence of Hr for these dot arrays indicated coherent rotation of the magnetization during nucleation. The effective magnetic anisotropy, including the demagnetizing energy due to the dot shape, Ku eff, decreased as the Pt content decreased, resulting in the Hr reduction. The values of the switching volume for nucleation, Vsw , evaluated from the stabilizing energy barrier E0, were a few percent of the dot volume. The switching diameter for nucleation, Dsw, increased slightly as the Pt content decreased, which was qualitatively in good agreement with the increase in the exchange length of magnetization. The value of E0/k BT (kB is the Boltzmann constant and T is the absolute temperature) reduced as the Pt content decreased; however, E 0/kBT still had a high of 440 even at 14 at% Pt content. We successfully demonstrated the reduction of Hr for CoPt/Ru patterned films on reducing the Pt content, while simultaneously maintaining a high thermal stability. A calculation based on the experimental results suggested the potential recording density of CoPt/Ru dot arrays used for patterned media to be over 1 Tb/in2 View full abstract»

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  • Magnetostriction Versus Magnetization of Hiperco 50 From 20 $^circ$C to 700 $^circ$C

    Page(s): 3886 - 3888
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    We report simultaneous measurement of magnetostriction and magnetization on strip samples of polycrystalline Hiperco 50 (49Fe 49Ni 2V, wt%) in fields of more than 300 Oe and over the temperature range from room temperature to 700degC. As a physical process, magnetostriction is clearly dependent on the state of magnetization of the sample, not on the applied magnetic field. From room temperature to about 500degC the magnetostrictive strain in Hiperco 50 is a quadratic function of the sample magnetization, and is only weakly dependent on temperature. Above 500degC, the maximum magnetostrictive strain drops fairly abruptly (as previously reported) from about 80 muepsiv to less than 30 muepsiv, and the shape of the strain versus magnetization plots changes shape, so that almost all the strain occurs near saturation magnetization View full abstract»

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  • Surface and Bulk Magnetic Hysteresis Loops of Co-Rich Glass Covered Microwires

    Page(s): 3889 - 3892
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    The magnetization reversal process in the surface and volume areas of Co-rich glass covered microwires has been investigated. The value of the helical anisotropy has been determined in two wires with different thickness of glass covering. The dependence of the coercive field on the frequency of the external axial magnetic field was studied in the surface and volume of the microwires View full abstract»

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  • Hall Biosensor With Integrated Current Microstrips for Control of Magnetic Beads

    Page(s): 3893 - 3895
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    Magnetic labeling of biomolecules shows potential as an alternative to fluorescence for monitoring molecular interactions associated with DNA hybridization and antibody-antigen analysis. Current carrying microstrips were integrated with micro-Hall biosensors to manipulate and collect superparamagnetic beads by field gradients generated due to direct currents passed through the strips. Magnetic beads with 2.8-mum diameters were collected over the active regions of AlGaAs/InGaAs heterostructure micro-Hall biosensors and detected in real time. The integration of current-carrying microstrips with Hall biosensors will decrease the time required for detecting biomolecular recognition processes in Hall sensor-based bioscreening platforms View full abstract»

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  • 2006 Index

    Page(s): 3897 - 4000
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  • IEEE Magnetics Society Information

    Page(s): c3
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  • IEEE Transactions on Magnetics institutional listings

    Page(s): c4
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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