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Magnetics, IEEE Transactions on

Issue 1 • Date Jan. 2006

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  • [Front cover]

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

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  • Table of contents

    Page(s): 1
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  • Effect of nitrogen incorporation to oxidation process on the reliability of magnetic tunnel junctions

    Page(s): 2 - 4
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    Magnetic tunnel junctions (MTJs) were fabricated using nitrogen-mixed oxygen plasma (O2:N2=10:1). From the measurements of time-dependent dielectric breakdown (TDDB) under a constant voltage stress, the reliability of MTJs with an oxy-nitride barrier was investigated and compared with that of MTJs fabricated using pure oxygen plasma. The reliability of MTJs with an oxy-nitride barrier is much improved with the incorporation of nitrogen to oxidation process. In addition, the reliability of the oxy-nitride barrier is gradually enhanced with increasing oxy-nitridation time even after the time exceeds the optimal value. It is believed that the enhancement is due to the bonding of nitrogen to electron traps both in the oxide barriers and at the bottom interface. The characteristics of the bonding were examined by XPS measurements, which reveal a nitrogen 1s peak in Al-N bond. The lifetime of the two barriers was also estimated for comparison. View full abstract»

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  • Effects of Ti on N distribution and diffusion in FeTiN thin films

    Page(s): 5 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    We studied the distribution and diffusion of N atoms in FeTiN single-layer and bilayer thin films by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We found that in as-deposited films N atoms are first absorbed by Ti atoms, the rest being dissolved into FeTi lattices. Ti not only directly absorbs N by chemical bonding, but also decreases the energy of the N atoms that are dissolved into FeTi lattices. The diffusion study of N atoms in single layer and bilayer films showed that although the presence of Ti stabilized the α phase of FeTi lattices during 200°C annealing, the diffusion length of dissolved N in FeTi (Ti≤8 at.%) lattices was still comparable to the diffusion length of N in pure Fe. Thus, the addition of a small amount of Ti in α-Fe lattice can not completely stabilize N atoms in the film, and the induced magnetic anisotropy of the films can still be unstable, although the α phase of FeTiN is stabilized by the addition of Ti. The distribution of N atoms in bilayer films can be fitted by a simple enthalpy model. View full abstract»

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  • A new class of magnetic fluids: bmim[FeCl4] and nbmim[FeCl4] ionic liquids

    Page(s): 12 - 14
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB) |  | HTML iconHTML  

    The responses to a magnet of two room-temperature ionic liquids containing tetrachloroferrate(III) ions, 1-butyl-3-methylimidazolium tetrachloroferrate (bmim[FeCl4]) and 1-butyronitrile-3-methylimidazolium tetrachloroferrate (nbmim[FeCl4]) are compared. Although their magnetic susceptibilities are similar, the observed responses are distinct from each other, suggesting that the response is determined not only by the magnetic susceptibility but also by the other factors including density, viscosity, and surface tension. The two magnetic ionic liquids constitute a new class of magnetic fluids that hold many attractive physical properties for practical applications. View full abstract»

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  • A quasi-static magnetic hysteresis loop measurement system with drift correction

    Page(s): 15 - 17
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    A method to overcome the residual drift problem inherent to M-H quasi-static hysteresis loop measurements is described. The solution is based on the magnetic hysteresis symmetry properties and was implemented in a computer-controlled inductive measurement system with frequency range 3-100 MHz for straight and circular samples particularly of soft amorphous and nanocrystalline alloys. Results obtained for several samples are presented showing the ability of the method to remove the residual drift. View full abstract»

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  • Analytic treatment of field diffusion into hysteretic magnetic materials

    Page(s): 18 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    This paper reapproaches the very classic problem of the analytic study of nonlinear diffusion of electromagnetic fields in conducting media. Significant contributions that appeared in the literature on this topic are cited in order to highlight the interest and the efforts provided by the scientific community on this topic as well as the aim and the main results of this work. The capabilities of two analytic procedures for estimating the energy losses in magnetic materials with hysteresis are shown and discussed. One formulation reduces the full nonlinear diffusion problem to a linear problem through an optimization procedure and is suited for thick cores. A second formulation approximates the magnetic field behavior by means of polynomials and provides good results for thin laminations. Energy losses are evaluated for magnetic materials with different B-H relations operating in wide frequency intervals. A scalar Preisach model, numerically treated, is used as a benchmark and, finally, calculations are compared with experimental data provided by other authors. View full abstract»

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  • Verification of high-order mixed finite-element solution of transient magnetic diffusion problems

    Page(s): 25 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1768 KB) |  | HTML iconHTML  

    We develop and present high-order mixed finite-element discretizations of the time-dependent electromagnetic diffusion equations for solving eddy-current problems on three-dimensional unstructured grids. The discretizations are based on high-order H(Grad), H(Curl), and H(Div) conforming finite-element spaces combined with an implicit and unconditionally stable generalized Crank-Nicholson time differencing method. We develop three separate electromagnetic diffusion formulations, namely the E (electric field), H(magnetic field), and the A-φ (potential) formulations. For each formulation, we also provide a consistent procedure for computing the secondary variables J(current flux density) and B(magnetic flux density), as these fields are required for the computation of electromagnetic force and heating terms. We verify the error convergence properties of each formulation via a series of numerical experiments on canonical problems with known analytic solutions. The key result is that the different formulations are equally accurate, even for the secondary variables J and B, and hence the choice of which formulation to use depends mostly on relevance of the natural and essential boundary conditions to the problem of interest. In addition, we highlight issues with numerical verification of finite-element methods that can lead to false conclusions on the accuracy of the methods. View full abstract»

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  • Accurately modeling EI core inductors using a high-fidelity magnetic equivalent circuit approach

    Page(s): 40 - 46
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    We present a high-fidelity magnetic equivalent circuit (HFMEC) inductor model that reduces the inaccuracies associated with a traditional MEC approach. The model can accurately predict the flux linkage versus current characteristic in a fraction of the time needed for finite-element analysis. The accuracy, computational efficiency, and simple inputs (consisting of only geometry and material specifications) make the model ideal for automated inductor design. View full abstract»

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  • A 64-kHz sandwich transducer fabricated using pseudo 1-3 magnetostrictive composite

    Page(s): 47 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB) |  | HTML iconHTML  

    A 64-kHz sandwich transducer employing a tube-shaped Terfenol-D/epoxy pseudo 1-3 magnetostrictive composite with 0.61 Terfenol-D volume fraction was developed to alleviate the intrinsic eddy-current losses in magnetostrictive alloy-based transducers. The transducer was designed to operate as a half-wave, longitudinal, mass-spring-mass, linear vibrator. It had a length of 15.7 mm and consisted of a magnetic circuit and a prestress mechanism. The magnetic circuit was composed of the composite tube, a pair of ring-shaped NdFeB permanent magnets, a drive solenoid, and a Ni-based magnetic flux guide. The distributions of the dc magnetic flux lines and magnetic field strength of the transducer were determined using an ANSYS finite-element model. The dynamic performance of the transducer was evaluated by measuring its electrical and vibrational characteristics. The results revealed that the transducer resonates at a frequency of 64.3 kHz with a strain coefficient of 39.2 nm/A, a mechanical quality factor of 39.6, and an effective coupling coefficient of 0.21. Eddy-current losses in the transducer were insignificant in the measured frequency range of 40 Hz-100 kHz. The good transducer performance indicated that Terfenol-D/epoxy pseudo 1-3 composites would be a promising magnetostrictive material for ultrasonic applications. View full abstract»

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  • Low-stress permalloy for magnetic MEMS switches

    Page(s): 51 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB) |  | HTML iconHTML  

    The residual stress in the electroplated magnetic films is an important factor that limits the functionality of many micromagnetic devices. We have investigated the stress in electroplated Ni-Fe alloy for MEMS as a function of bath concentration, utilizing the wafer-bending method. Our investigation demonstrated that a low-concentration plating solution decreases the residual stress in the electrodeposits, and the stress is further decreased by increasing the saccharin additive content. We obtained the low-stress Permalloy Ni81Fe19 in our experimental conditions. We fabricated a bistable electromagnetic RF MEMS switch with deformation-free cantilever beam using the electroplated Permalloy. View full abstract»

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  • A new approach to micromagnetic simulation of thermal magnetic fluctuation noise in magnetoresistive read sensors

    Page(s): 56 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1176 KB) |  | HTML iconHTML  

    Thermal magnetic fluctuation noise forms the ultimate application limit of small magnetoresistive devices for magnetic data storage. The noise analysis of these devices becomes increasingly important for high-density recording. Such noise analyses by micromagnetic simulation are, however, computationally very intensive and require enormous amounts of simulation time. This paper presents a faster micromagnetic method to arrive at the noise and small signal dynamics of these sensors. It uses, for every cell in the simulation, a behavioral analog (i.e., an "analog computer" model) described by the same equations as the basic magnetic simulation cell (the Landau-Lifshitz-Gilbert equation, Slonczewski's spin torque addition and the equipartition principle). The sensor, as a network of exchange and demagnetization coupled cells, is then solved with a network simulator (such as PSpice). This process gives a drastic reduction in computing time and yet leads to high resolution spectra with very little residual uncertainty. The paper further presents a large number of simulation results for uniform sensors as well as for sensors with a nonuniform magnetic bias and a nonuniform electrical bias. It addresses the spatial distribution of the noise (standing spin waves in the noise) and the correlation of the noise in various parts of the sensors. Finally, as a further example of this method, the paper shows the effect of spin torque transfer on the noise and the small signal dynamics of a current perpendicular to plane giant magnetoresistive (CPP GMR) sensor. View full abstract»

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  • Joint design of optimum partial response target and equalizer for recording channels with jitter noise

    Page(s): 70 - 77
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    We address joint design of optimum generalized partial response (GPR) target and equalizer for perpendicular recording channels with jitter noise. We develop a new cost function which accounts for the data-dependent nature of jitter noise based on the minimum mean square error (MMSE) criterion. Using the step-response-based channel model, we derive expressions for the statistics required to compute the optimum equalizer and target in the presence of jitter noise. We also derive a bit-response-based model for the jitter noise channel. We present an approach for doing simulations as well as analytical computations for the jitter noise channel without resorting to the widely used Taylor series approximations. Our computational and simulation results show that, while the targets designed without accounting for the jitter lead to error-floor effect in the bit-error-rate performance, the targets designed by our approach give significant performance improvement under high jitter conditions, with no sign of error-floor effect for the range of signal-to-noise ratios considered. View full abstract»

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  • Magnetic and magnetoelastic properties of melt-spun Ni-Mn-Ga

    Page(s): 78 - 80
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    We have fabricated single roller melt-spun ribbons of the ferromagnetic shape memory alloy NiMnGa. The ribbons' magnetic and magnetoelastic responses and corresponding microstructure in the as-spun and annealed states were analyzed by a combination of vibrating sample magnetometry, X-ray diffraction, differential scanning calorimetery, capacitance dilatometry, and optical microscopy. The transformation strain in the annealed ribbons showed a dependence on the applied field of 600 ppm, whereas the as-spun samples did not display any field-induced strain. View full abstract»

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  • X-ray diffraction technique to observe magnetostriction and magnetization at coextensive volumes of iron

    Page(s): 81 - 83
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    We present a new technique for observing both magnetostriction and magnetization as a function of applied magnetic field strength. They are simultaneously measured by the same X-ray probes with a goniometer at exactly coextensive specimen volumes. The measurements yield experimental magnetostriction curves during a cyclic magnetization process in iron (100) single-crystal specimen at room temperature. The technique is a new tool to investigate magnetic properties within X-ray extinction depth from the surface. View full abstract»

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  • Analytical equivalent impedance for a planar circular induction heating system

    Page(s): 84 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    A set of analytical expressions is derived for the equivalent impedance in a planar circular induction heating system, used for example in home appliances. The induction system consists of an n-turn planar winding loaded by a conductive material. Expressions that describe the frequency dependence of impedance are provided. The influence of load conductivity, load permeability, and geometrical dimensions is also considered. Validation of the proposed model is carried out through experimental measurements. View full abstract»

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  • IEEE Magnetics Society & The IEEE Press call for books

    Page(s): 87
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    Page(s): 88
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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