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Magnetics, IEEE Transactions on

Issue 11 • Date Nov. 2006

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Displaying Results 1 - 25 of 33
  • [Front cover]

    Publication Year: 2006 , Page(s): c1
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  • IEEE Transactions on Magnetics publication information

    Publication Year: 2006 , Page(s): c2
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  • Table of contents

    Publication Year: 2006 , Page(s): 3633 - 3634
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  • Complex Permittivity and Permeability of Co _2 U (Ba _4 Co _2 Fe _36 O _60 ) Hexaferrite Bulk and Composite Thick Films at Radio and Microwave Frequencies

    Publication Year: 2006 , Page(s): 3635 - 3640
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1408 KB) |  | HTML iconHTML  

    We measured dielectric, magnetic, and microwave properties of Co 2U hexaferrite (Ba4Co2Fe36O 60) polycrystalline bulk and composite thick film samples, and studied the effect of annealing temperature on phase formation and microstructure. We synthesized the bulk samples from a precursor prepared by the citrate method. The values of dielectric constant at radio frequencies (50 Hz-1 MHz) of the bulk Co2U12 sample sintered at 1200degC are much higher, and the resistivities are lower, compared to M-type barium hexaferrites. Coercivity is also low, having a value of 5 G for the Co2U12 sample, whereas the saturation magnetization value is 59 emu/g, which is comparable to that of M-type hexaferrites. We also measured the complex permittivity and permeability for Co2U12 samples at microwave frequencies and found the values high compared to M-type barium hexaferrite at these frequencies. Thick composite films were prepared from a ferrite-polymer mix, and all the above properties were studied for these films. We observed that these thick films have lower values of dielectric and magnetic parameters both at low and microwave frequencies. We measured microwave-absorbing properties for the ferrite-polymer sample (ferrite to polymer ratio 70/30) which showed a maximum reflection loss of -37.5 dB at 11.5 GHz for the 3.5-mm-thick sample View full abstract»

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  • Flux-Closure Magnetic States in Triangular Cobalt Ring Elements

    Publication Year: 2006 , Page(s): 3641 - 3644
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1326 KB) |  | HTML iconHTML  

    Ferromagnetic ring elements on the micrometer and submicrometer scale exhibit flux-closure magnetic vortex states in an intermediate step of their magnetization reversal. These clockwise or counterclockwise flux-closure states are of interest for applications that encode binary information in magnetic elements. Here, we study the magnetization reversal process of triangular cobalt rings made by e-beam lithography and lift-off. We demonstrate that full control over the direction of flux-closure magnetic states can be achieved solely by homogeneous external magnetic fields applied in particular directions. We have extracted statistical experimental data pertaining to the range of critical field values that trigger magnetization reversal from magnetic force microscopy images, and we explain the results on the basis of micromagnetic simulations View full abstract»

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  • Evaluating the Permeability Distribution of a Layered Conductor by Inductance Spectroscopy

    Publication Year: 2006 , Page(s): 3645 - 3651
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB) |  | HTML iconHTML  

    This paper presents an inverse method for determining the permeability distribution of a flat, layered conductor by using a multifrequency electromagnetic sensor. It discusses the use of spectroscopic techniques to extract depth profiles and examine more fully the internal structure of the test piece. The forward solution for a small right-cylindrical air-cored coil placed next to a layered conductor is based on the analytic solution provided by the transfer matrix approach. For the inverse solution, a modified Newton-Raphson method is used to adjust the permeability profile to fit a set of multifrequency inductances in a least-squared sense. The approximate Jacobian matrix (sensitivity matrix) is obtained by the perturbation method. The paper provides numerical results of the forward solution for cases of step and continuous permeability profiles. Inverse results based on experimental and simulated data verify the accuracy of this method, which yields good estimates for the permeability profile View full abstract»

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  • Magnetization Switching With Nonstandard Dissipation

    Publication Year: 2006 , Page(s): 3652 - 3656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    We report on our study of magnetization switching in a single-domain ellipsoidal particle. Under the assumption of uniaxial anisotropy collinear with the applied field, we derive an explicit formula for the switching time from the Landau-Lifschitz equation for a class of dissipation mechanisms that includes Gilbert's, dry friction, and others. While some dissipation is essential to finite-time switching, we show that too much of it would be detrimental, in that it would lengthen the time required to switch, no matter what mechanism is chosen in the class under study View full abstract»

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  • Bayesian Inference Approach to Particle Size Distribution Estimation in Ferrofluids

    Publication Year: 2006 , Page(s): 3657 - 3660
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (139 KB) |  | HTML iconHTML  

    We present an effective direct extraction method for particle size distribution based on Bayesian inference theory with a free-form model. We give an example of the application to the particle size distribution analysis in ferrofluid consisting of cobalt particles in toluene. The method gives a unique solution to the distribution without assuming the shape of the distribution of the particle size View full abstract»

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  • Time-Domain Dyadic Green's Function for an Electric Source in a Conductive Plate

    Publication Year: 2006 , Page(s): 3661 - 3668
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (617 KB) |  | HTML iconHTML  

    We have determined the quasi-static time-domain dyadic Green's function for an electric source in a conductive plate for use in electric field integral equations. Starting with a frequency-domain representation, we constructed the dyadic kernel from electric and magnetic scalar potentials defined with respect to a preferred direction normal to plate. The final time-domain expression has three parts: a free-space term, multiple image terms, and partial reflection terms. The free-space fundamental solution is expressed in terms of a three-dimensional Gaussian bell curve satisfying the diffusion equation. Similarly, the image terms are expressed in the same form with coordinates shifted so that each Gaussian curve centers on an image point. In order to carry out the inverse Laplace transform from the frequency domain to the time domain, we expand the partial reflection functions as asymptotic series before transforming them analytically. The resulting expression for dyadic Green's kernel can be evaluated efficiently and with well-controlled accuracy View full abstract»

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  • Theoretical Lower Error Bound for Comparative Evaluation of Sensor Arrays in Magnetostatic Linear Inverse Problems

    Publication Year: 2006 , Page(s): 3669 - 3673
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    We introduce a theoretical lower error bound for solutions to magnetostatic linear inverse problems and we propose it as a figure of merit for the comparative evaluation of sensor arrays. With the help of the proposed error bound, we demonstrate the superiority of three-axial biomagnetic sensor arrays applying truncated singular value decomposition analysis to a kernel matrix computed from boundary-element-method (BEM) models of the human torso for a biomagnetic application. In simulations, we found that, for a more complex five-compartment BEM model, the advantage of using three-axial measurements is more pronounced, compared to a three-compartment BEM model View full abstract»

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  • A New Approach for Finite-Element Modeling of Hysteresis and Dynamic Effects

    Publication Year: 2006 , Page(s): 3674 - 3681
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB) |  | HTML iconHTML  

    Macroscopic behavior of ferromagnetic materials can be considered as the resultant of three phenomena: hysteresis, eddy current, and excess loss. Hysteresis is the behavior of the material under quasi-static variation of magnetic field. Eddy-current and excess losses are dependent on the rate of field variation and are evident in the fast variation of the magnetic field, so they are called dynamic effects. This paper presents a simple and practical technique in field analysis of electromagnetic systems having hysteresis and dynamic effects. Based on the Preisach model for hysteresis and existing formulations for eddy currents and excess loss, an equivalent expression for field intensity has been introduced. A new technique has been presented in order to include this expression in the finite-element code. A typical system has been modeled by this code. Effects of relaxation and time step were examined on the stability and the convergence rate of the method. The validity of the proposed model has been checked by comparing its results with experimental measurements View full abstract»

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  • Calculation and Analysis of the Magnetic Force Acting on a Particle in the Magnetic Field of Separator. Analysis of the Equations Used in the Magnetic Methods of Separation

    Publication Year: 2006 , Page(s): 3682 - 3693
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1296 KB) |  | HTML iconHTML  

    This paper presents the derivation of equation for calculating the magnetic force acting on a paramagnetic ball situated in a region of a nonuniform magnetic field. We suggest the method of its extrapolation to the case of a nonlinear medium-the case of a ferromagnetic ball found under the influence of the magnetic field which is varying in a certain properly defined range. An experimental setting intended for the measurement of the magnetic force is described as well. For the first time a rigorous proof of the isodynamic magnetic field inexistence, that is a field which generates a magnetic force having the same constant direction and the same constant magnitude at each space point, is given. Moreover, using the method of conformal mappings we derive the analytic expressions for the magnetic field strength calculation in the case of a multipole system. With their help, different important features of the magnetic field behavior in this case are elucidated. The latter is done in a wide region of the geometric parameter space of the magnetic system. The interpretations of different issues discussed in the paper are compared to those that seems to be widely accepted in the magnetic methods of separation branch View full abstract»

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  • Recurrent Radial Basis Function Network-Based Fuzzy Neural Network Control for Permanent-Magnet Linear Synchronous Motor Servo Drive

    Publication Year: 2006 , Page(s): 3694 - 3705
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB) |  | HTML iconHTML  

    We propose a recurrent radial basis function network-based (RBFN-based) fuzzy neural network (FNN) to control the position of the mover of a field-oriented control permanent-magnet linear synchronous motor (PMLSM) to track periodic reference trajectories. The proposed recurrent RBFN-based FNN combines the merits of self-constructing fuzzy neural network (SCFNN), recurrent neural network (RNN), and RBFN. Moreover, it performs the structureand parameter-learning phases concurrently. The structure learning is based on the partition of input space, and the parameter learning is based on the supervised gradient descent method, using a delta adaptation law. Furthermore, all the control algorithms are implemented in a TMS320C32 DSP-based control computer. The simulated and experimental results due to periodic reference trajectories show that the dynamic behaviors of the proposed recurrent RBFN-based FNN control system are robust with regard to uncertainties View full abstract»

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  • Mitigation of Torque Ripple in Interior Permanent Magnet Motors by Optimal Shape Design

    Publication Year: 2006 , Page(s): 3706 - 3711
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB) |  | HTML iconHTML  

    Optimal shape design of an interior permanent-magnet (IPM) synchronous motor can substantially reduce its torque pulsation. However, the shape design variations should be feasible and practical. We report on an optimal shape design obtained by drilling small circular holes in the rotor. We found that an optimal location and radius of the holes effectively suppresses the torque pulsation of the IPM drive for various loads under steady-state conditions. The optimal design at rated load is considered as the final design. We use a transient finite-element analysis that is coupled with motion and adequate electric excitation for optimization purposes. An evaluation of the optimal design at various operating conditions showed torque ripple reduction and average torque improvement under all load conditions. The optimal design also shows improvement in the field-weakening region for high-speed operation View full abstract»

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  • A Comparative Analysis of Two Test Methods of Measuring d - and q -Axes Inductances of Interior Permanent-Magnet Machine

    Publication Year: 2006 , Page(s): 3712 - 3718
    Cited by:  Papers (37)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1307 KB) |  | HTML iconHTML  

    The interior permanent-magnet (IPM) machine is used in many industrial drives. In order to analyze performance and to design efficient and fast controllers, accurate knowledge of machine parameters such as d- and q-axes inductances is essential. Although there are a number of methods available to calculate these inductances, none of them is considered standard. Accuracy levels of all these methods are also not consistent, and some of the measurement methods require complicated arrangements. Among these test methods, the ac standstill test and a newly developed test method that uses vector current control technique are ideal for a laboratory environment. In this paper, these two methods are compared by applying them to a prototype IPM machine. The paper analyzes the test results of the methods and their differences in detail with the help of finite-element analysis View full abstract»

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  • Modeling of Planar Spiral Inductors Between Two Multilayer Media for Induction Heating Applications

    Publication Year: 2006 , Page(s): 3719 - 3729
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1146 KB)  

    We present an analytical model of the equivalent impedance of an n-turn planar winding sandwiched between top and bottom multilayer media. Although the model's general and compact notation is valid for all systems involving magnetic dipoles and stratified media, perhaps its main application is domestic induction heating systems. The proposed model is based on the vector potential solution of a single-turn coil located between two multilayer media, and this result is extended to n-turn coils. We demonstrate the applicability of the model by a variety of examples. We present experimental results to justify the theoretical model View full abstract»

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  • Fast Calculation of Field Currents and Reactances for Doubly Fed Generators With Rotor Duct Pieces

    Publication Year: 2006 , Page(s): 3730 - 3736
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1330 KB) |  | HTML iconHTML  

    Doubly fed generators have been used as adjustable-speed pumped-storage generator motors and wind turbine generators. Accurate determination of field currents and reactances is important for the design of these machines. We propose a calculation method to obtain the field currents and reactances of machines with rotor duct pieces under any steady-state balanced load condition. The method links two-dimensional static finite-element analysis (FEA) with an approximate calculation to consider three-dimensional (3-D) skin effect in the duct pieces. Its advantage is that the computational time is much smaller than 3-D transient FEA when the slip frequency is not zero. The method will contribute to improvement of the design of doubly fed generators with rotor duct pieces. It was applied to a 395 MVA machine, and the calculated field currents agreed well with the measurements. Variation in the reactances due to saturation is also discussed View full abstract»

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  • A Parametric Study of Magneto-Optic Imaging Using Finite-Element Analysis Applied to Aircraft Rivet Site Inspection

    Publication Year: 2006 , Page(s): 3737 - 3744
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1028 KB) |  | HTML iconHTML  

    Magneto-optic/eddy current imaging (MOI) has become increasingly popular for inspecting aging aluminum airframes for cracks and corrosion due to its accuracy, reliability, and ease of use. As inspection requirements change, modifications to the MOI system must be made to improve sensitivity and resolution to reliably detect smaller and/or deeper defects in the aircraft structure. Incorporating such improvements by "cut and try" methods is time-consuming and expensive. Therefore, a numerical simulation model that produces quantitative values of the magnetic fields associated with induced eddy currents interacting with structural defects is an essential complement to the instrument development process. Such a model provides a convenient tool for parametrically evaluating the effectiveness of the MOI for detecting various structural defects. This paper presents a three-dimensional finite-element model of Maxwell's equations, utilizing the A-V formulation for numerical simulation of the MOI operation. The model is used to predict quantitative values of field distributions that produce the binary magneto-optic images of subsurface fatigue cracks at rivet sites in an aluminum airframe structure. A parametric study is performed to determine the effects of MOI operational parameters on the binary images. A skewness parameter based on the binary images is established to provide a measure of defect size. This parameter will prove useful for automatic detection and classification of defects. The model-generated images show good agreement with experimentally derived MOI images View full abstract»

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  • Optimal Narrow-Band Disturbance Filter for PZT-Actuated Head Positioning Control on a Spinstand

    Publication Year: 2006 , Page(s): 3745 - 3751
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (601 KB) |  | HTML iconHTML  

    Narrow-band position error at midfrequencies around the open-loop crossover frequency cannot be effectively reduced by using a conventional peak filter, because the attenuation of sensitivity gains has to be traded off with the associated decrease of phase margin. This paper presents a general second-order filter that can reject narrow-band disturbances at any frequency range. The filter zero is designed to minimally degrade the closed-loop system stability and obtain a smooth sensitivity curve around the disturbance frequency. The paper presents a nonlinear optimization procedure for selecting the filter parameters so that the statistical position error is minimized. Experimental results of a piezoelectrically actuated head positioning control system on a spinstand demonstrate that the add-on filter can further reduce the midfrequency nonrepeatable runout of the position error signal by 8% and preserve the stability margin of the original feedback control system View full abstract»

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  • Data-Aided Timing Recovery for Recording Channels With Data-Dependent Noise

    Publication Year: 2006 , Page(s): 3752 - 3759
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    In high-density data storage systems, noise becomes highly correlated and data dependent as a result of media noise, channel nonlinearities, and front-end filters. In such environments, conventional timing recovery schemes will exhibit large residual timing jitter and, especially, data-dependent timing jitter. This paper presents a new data-aided timing recovery algorithm for data storage systems with data-dependent noise. We derive a maximum-likelihood timing recovery scheme based on a data-dependent Gauss-Markov model of the noise. The timing recovery algorithm incorporates data-dependent noise prediction parameters in the form of linear prediction filters and prediction error variances. Moreover, because noise can be nonstationary in practice, we propose an adaptive algorithm to estimate and track the noise prediction parameters. Simulation results, for an idealized optical storage channel incorporating a simple model of media noise, illustrate the merits of our algorithm View full abstract»

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  • Switched Reluctance Machines as Three-Phase AC Autonomous Generator

    Publication Year: 2006 , Page(s): 3760 - 3764
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (387 KB)  

    The operation of the switched reluctance machine as an autonomous three-phase ac generator is considered. Two circuits are proposed. The generator circuit consists of only capacitors and load supplementary to the generator, but does not contain any power supply. Theoretical approaches for simulation of the three-phase autonomous switched reluctance generator are presented. The influence of the high harmonics in the phase current on the power output is discussed. Experimental and simulation results are presented View full abstract»

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  • A Note on “Signal-to-Noise Ratio Mismatch for Low-Density Parity-Check Coded Magnetic Recording Channels” by W. Tan and J. R. Cruz

    Publication Year: 2006 , Page(s): 3765 - 3766
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (59 KB) |  | HTML iconHTML  

    In this letter, we prove that the minimum signal-to-noise ratio (SNR) threshold of the iterative belief propagation algorithm for a low-density parity-check (LDPC) coded magnetic recording channel is obtained when the SNR mismatch factor is half the ratio of variance to mean for the Gaussian distribution at the channel output. This result was first observed by Tan and Cruz empirically View full abstract»

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  • Structural and Magnetic Properties of Sm _3 (Fe _1-\rm x Co \rm _ x ) _27.7 Ti _1.3

    Publication Year: 2006 , Page(s): 3767 - 3769
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (147 KB) |  | HTML iconHTML  

    The structure and magnetic properties of Sm3(Fe1-x Cox)27.7Ti1.3 compounds, with x ranging from 0 to 0.4, have been investigated by means of X-ray powder diffraction and magnetic measurements. The main phase formed was that of Nd3(Fe, Ti)29-type structure (3:29) with a relatively small amount of the ThMn12-type structure (1:12) as a secondary phase (7-13 wt.%). The lattice parameters and the unit-cell volume decrease with increasing Co content x. It is found that substitution of Co for Fe leads to a significant increase in the Curie temperature from 488 K for x=0 to 941 K for x=0.4. Saturation magnetization gradually increases with increasing Co. All compounds show easy cone-type anisotropy View full abstract»

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  • The (SmZr)Co _3 Phase in Sm(CoFeCuZr) \rm _ z Magnets

    Publication Year: 2006 , Page(s): 3770 - 3772
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (527 KB) |  | HTML iconHTML  

    Detailed microstructural characterization of magnets and homogenized as-cast alloys, which included X-ray diffraction Rietveld analysis, has indicated that the so-called platelet or lamellae phase is (SmZr)1(CoFeCu)3 with the PuNi3 structure and lattice parameters a~0.5 nm and c~2.4 nm. The structural and magnetic properties of the (SmZr)Co3 phase were investigated. The microstructure shows two phases differing in their Zr/Sm ratio. Magnetization curves for the samples (Sm0.33Zr 0.67)Co3, (Sm0.33Zr0.67)Co 2.97Fe0.03, and (Sm0.67Zr0.33)Co3 are consistent with the two-phase microstructure observed. Room temperature coercivity values of these samples are low (ap1 kOe.) View full abstract»

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  • Stress Induced Enhancement of Magnetization Reversal Process of DyFeCo Films With Perpendicular Magnetization

    Publication Year: 2006 , Page(s): 3773 - 3775
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (207 KB) |  | HTML iconHTML  

    A method to control magnetization reversal in magnetic films with perpendicular magnetic anisotropy was demonstrated in this study. Alloys of rare earth-transition metals (RE-TM) with their extremely large anomalous Hall coefficient and relatively large magnetostriction constants were suitable to observe the stress induced anisotropy using anomalous Hall effect. Stress applied to the RE-TM thin films significantly reduced the perpendicular coercivity and nucleation field of the film in comparison with that of the film in stress-free condition. Dyx(Fe90Co10)1-x thin films revealed large Hall voltage and remarkable change in the coercivity under the mechanical tensile stress 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