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Magnetics, IEEE Transactions on

Issue 3  Part 2 • Date March 2010

 This issue contains several parts.Go to:  Part 1 

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  • [Front cover]

    Publication Year: 2010 , Page(s): C1
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  • IEEE Transactions on Magnetics publication information

    Publication Year: 2010 , Page(s): C2
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  • Table of contents

    Publication Year: 2010 , Page(s): 845 - 846
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  • Nanocrystalline Spinel Mn _{x} Cu _{1 - x} Fe _{2} O _{4} Ferrites—Synthesis and Structural Elucidation Using X-Ray Diffraction and Positron Annihilation Techniques

    Publication Year: 2010 , Page(s): 847 - 851
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (165 KB) |  | HTML iconHTML  

    We have synthesized a series of nanocrystalline ferrite samples with the composition MnxCu1-xFe2O4 (x=0.2, 0.4, 0.6, 0.8) by an advanced sol-gel auto-combustion method. The X-ray diffraction patterns confirm the existence of single-phase cubic spinel crystal structure of ferrites with lattice parameter ranges from 8.395 ?? to 8.45 ??. We report the equilibrium radii for tetrahedral and octahedral sites in the unit cells and the estimated cation distribution over the two sites of nanocrystalline MnxCu1-xFe2O4. We also estimate the oxygen positional parameter as 0.389. The positron annihilation life time spectroscopic studies were carried out for all the samples and analyzed the variation of life time parameters ??1; I1, ??2; I2 and the mean life time ??m to elucidate the defect structure of the nanocrystalline MnxCu1-xFe2O4. We found that the overall vacant type defects fill up as the Mn2+ ion concentration, x, increases. The value of ??1 varies from 150 ps to 170 ps and that of ??2 varies from 295 ps to 335 ps, which are the characteristic values for nanocrystalline samples, indicating the presence of intergranular as well as surface-diffused vacancies in the crystal structure. View full abstract»

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  • Effect of Sample Concentration on the Determination of the Anisotropy Constant of Magnetic Nanoparticles

    Publication Year: 2010 , Page(s): 852 - 859
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (561 KB) |  | HTML iconHTML  

    Techniques such as equilibrium (DC) and dynamic (AC) magnetic measurements have been used to determine the anisotropy constant of a variety of magnetic nanoparticles, obtaining values that are often an order of magnitude higher than the corresponding bulk material. Unfortunately, the effect of particle-particle interactions is often neglected, hence the reported values are an effective collective parameter , rather than an intrinsic property. In this study we used DC and AC magnetic measurements to determine the anisotropy constant of magnetic nanoparticles fixed in a cross-linked polymer matrix. We used nanoparticle concentrations of 0.1%, 1%, 6%, and 33%(w/w) in order to determine the effect of concentration, and hence interactions, on the value determined for the anisotropy constant. The effect of interaction on determining the magnetocrystalline anisotropy constant was accounted for by using the Ne?el and Vogel-Fulcher relaxation models, the latter with an effective interaction temperature determined from independent measurements. A decrease in the anisotropy constant determined from these measurements was observed with decreasing particle concentration from ~ 6100 kerg/cm3 to ~ 500 kerg/cm3 using the Vogel-Fulcher model and from ~ 9100 kerg/cm3 to ~ 1100 kerg/cm3 using the Ne?el model. The values obtained for the most dilute samples using the Vogel-Fulcher model are of comparable magnitude to bulk values for magnetite. More importantly, the value of ?0 obtained from AC susceptibility decreased from 10-32 to 10-9 s with decreasing particle concentration. As ?0 is expected to be of the order of 10-9 s, these results indicate that the value of magnetic anisotropy determined for the dilute sample represents an intrinsic rather than effective property. These measurements and analysis illustrate the importance of particle concentration/interactions in determining the in- - trinsic magnetic properties of nanoparticles, particularly the anisotropy constant . View full abstract»

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  • Spin Transfer Torque Memory With Thermal Assist Mechanism: A Case Study

    Publication Year: 2010 , Page(s): 860 - 865
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    We have investigated spin transfer torque random access memory (STT-RAM) with a thermal-assist programming scheme using finite-element thermal simulation. We conducted the study on a specific memory element design to analyze the thermal dynamics and thermal programming mechanism. We paid particular attention to the scalability and design potential of the thermal-assist programming scheme by varying the memory element dimension and resistance-area product. In addition we systematically analyzed and compared thermal-assisted STT-RAM and standard STT-RAM based on these results. Finally, we provide a summary of the programming scheme and some recommendations for improving writeability and scalability of this technology. View full abstract»

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  • Measuring Entropy Generated by Spin-Transfer

    Publication Year: 2010 , Page(s): 866 - 874
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (755 KB) |  | HTML iconHTML  

    We present an experimental protocol that allows the entropy generated by spin-transfer to be measured. We investigate the effect of strong spin injection on a ferromagnetic nanostructure, focusing on the quasi-static equilibrium states of a single magnetic domain. We measure the response of the magnetoresistance to a temperature excitation as a function of the magnetic field for different values of the injected current. This quantity is related to the thermal susceptibility of the ferromagnetic wire through the anisotropic magnetoresistance. We deduce the ferromagnetic entropy generated by spin injection by a thermodynamic Maxwell relation. We applied this protocol to single contacted Ni nanowires obtained by electrodeposition in a nanoporous template. We observe that the entropy produced by the spin injection is a linear function of the current and reaches 60% of the initial entropy of the system for 5 ?? 107 A/cm2. This study shows that the effect of the spin-transfer in these samples results in the generation of incoherent excitations instead of rotation of the magnetization. View full abstract»

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  • Using the Newton–Raphson Method in the Polarization Technique to Solve Nonlinear Static Magnetic Field Problems

    Publication Year: 2010 , Page(s): 875 - 879
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    The paper presents and compares three potential formulations to solve nonlinear static magnetic field problems by applying the fixed point technique and the Newton-Raphson scheme. Nonlinear characteristics are handled by the polarization method in both algorithms. The proposed combination of the Newton-Raphson scheme and the polarization formulation results in a very effective nonlinear solver, because only the derivate of the characteristics, i.e., only the permeability or the reluctivity has to be used. Therefore, this method can be used to solve nonlinear problems with hysteresis, and it is faster than the classical fixed point method. View full abstract»

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  • Bulletpack: A Fast, Flexible Packing Algorithm for Particulate Media

    Publication Year: 2010 , Page(s): 880 - 885
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1293 KB) |  | HTML iconHTML  

    We introduce a new particle packing code that mimics the process used to fabricate particulate media. It achieves realistic packing fractions, with values well above 40%, and high computational efficiency for nearly arbitrary particle shapes and distributions of geometric and magnetic properties. We perform recording simulations in combination with a modified version of the Magpar micromagnetic code to illustrate the importance of realistic packing. We find for the case of non-oriented platelets that the broadband signal-to-noise ratio drops by 1 dB when the packing fraction is reduced from 43% to 30%; this result is in agreement with scaling models. View full abstract»

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  • A New Shorted Microstrip Method to Determine the Complex Permeability of Thin Films

    Publication Year: 2010 , Page(s): 886 - 888
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (193 KB) |  | HTML iconHTML  

    A new method is proposed to determine the complex permeability of ferromagnetic thin films from 100 MHz to 15 GHz. In this method, shorted microstrip transmission-line perturbation combined with the conformal mapping method is used. In contrast with previous methods to measure the thin films deposited on rigid substrates, this method neither requires any reference sample for calibration, nor requires the additional measurement to determine saturation magnetization. To assess the validity of this new method, three samples with different thicknesses are measured; comparisons are performed between the theoretical and experimental results, and the repeatability of this method is studied by measuring the samples five times. The results show that the complex permeability of ferromagnetic thin films can be measured within 10% errors. View full abstract»

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  • Nonferromagnetic Open Shields at Industrial Frequency Rate

    Publication Year: 2010 , Page(s): 889 - 898
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1395 KB) |  | HTML iconHTML  

    We have investigated some innovative geometric configurations for shielding extremely low-frequency (ELF) magnetic fields through nonferromagnetic materials. We define proper 2-D and 3-D finite-element (FE) models for the numerical computation of the shielding effectiveness of open conducting shields, in order to assess the mitigation of the magnetic field generated by a single-wire transmission line, two-wire t.l., or three-phase current excitation at industrial frequency rates. For the case of current conductors in air (i.e., in absence of the metallic shield) we validate our numerical model using the Biot-Savart law, while for the case of an infinite plane shield we exploit an analytical validation by means of a direct solution of the Maxwell's equations, with properly defined boundary conditions. We compare our experimental results with those found in literature and prove the accuracy of the computed shielding efficiency. After this preliminary validation of the numerical tool, we study the behavior of several nonplane open shields, characterized by different transversal profiles: by means of the FE model, we directly compare these innovative configurations to the plane one, thus showing that they can guarantee an increase of the shielding effectiveness at constant weight of the shield just by a simultaneous mitigation of both the two components of the magnetic field in the transversal plane. This feature is verified by means of experimental results, in which we have considered a finite shield with a current source constituted by a single long wire. View full abstract»

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  • Determination of Hardness and Residual-Stress Variations in Hardened Surface Layers With Magnetic Barkhausen Noise

    Publication Year: 2010 , Page(s): 899 - 904
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (557 KB) |  | HTML iconHTML  

    We use magnetic Barkhausen noise to assess the microstructure, hardness, and residual stresses in hardened surface layers. We performed measurements on induction surface-hardened specimens, the thickness of hardened layers being different in each case. A change in the microstructure of the hardened surface layer produces changes in specific electric conductivity ?? and relative permeability ??r . The two parameters and chosen analyzing frequencies influence the depth sensing of micromagnetic changes. The most commonly chosen characteristic of Barkhausen noise is the V2 RMS value of a captured signal. The choice of frequency determines the depth at which the Barkhausen noise will be analyzed to determine microhardness or residual stresses. View full abstract»

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  • Finite-Element Model for Simulation of Ferrite-Core Eddy-Current Probe

    Publication Year: 2010 , Page(s): 905 - 909
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (341 KB) |  | HTML iconHTML  

    The finite-element method is widely used in modeling eddy-current phenomena. However, its application in eddy-current nondestructive testing involving probe motion requires remeshing for each coil position. Remeshing is not only cumbersome but also a major source of computational noise. We have used the reduced magnetic vector potential formulation to model an air-core probe scan without remeshing the coil in different positions. In this paper, we present a method to model the scanning of ferrite-core probe. With this method, finite-element meshes for the test sample and the ferrite core are generated separately. The coil is not meshed. The magnetic field and magnetic vector potential due to the coil are evaluated analytically. An iterative but fast procedure is used to update the total field. The method is simple, flexible, accurate, and efficient. View full abstract»

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  • Pulsed Eddy-Current Based Giant Magnetoresistive System for the Inspection of Aircraft Structures

    Publication Year: 2010 , Page(s): 910 - 917
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1099 KB) |  | HTML iconHTML  

    Research in nondestructive evaluation is constantly increasing the sensitivity of detection of small cracks embedded deep in layered aircraft structures. Pulsed eddy-current (PEC) techniques using coil probes have shown considerable promise in detection and characterization of buried cracks in multilayered structures. In this paper, we describe the design and development of a nondestructive inspection system that uses pulse excitation of a planar multiline coil to generate a transient field that is detected via a giant magnetoresistive (GMR) field sensor. An analysis algorithm using features in time and frequency domain processes the experimentally measured signals for automatic detection of small cracks under fasteners in multilayered structures at a depth of up to 10 mm. View full abstract»

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  • Improving Loss Properties of the Mayergoyz Vector Hysteresis Model

    Publication Year: 2010 , Page(s): 918 - 924
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    We present a new method for improving the magnetic loss properties of a certain class of isotropic vector hysteresis models based on the Mayergoyz model. We show that the Mayergoyz model possesses the necessary features for representing vector hysteresis but falls short of satisfying the loss property under rotating magnetic fields with magnitudes close to saturation. Therefore, we propose a new simple method to improve the loss property of the Mayergoyz model while keeping the essential features of the model. The method is based on removing the irreversible process persisting at saturation and hence correcting the magnetization behavior of the Mayergoyz model. We present thorough discussions about the properties of the new model as well as numerical results supported by experiments. View full abstract»

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  • Observing the Magnetization Distribution in the Pseudo Soft Underlayer of Perpendicular Magnetic Recording Media by Electron Holography

    Publication Year: 2010 , Page(s): 925 - 927
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (661 KB) |  | HTML iconHTML  

    We visualized the magnetic flux density of the cross track direction in the pseudo soft underlayer (SUL) of perpendicular magnetic recording media. We deposited a pseudo-SUL on the fabricated slider of a perpendicular magnetic recording head, and used electron holography to visualize and quantify the magnetic flux magnitude and distribution in the pseudo-SUL. We observed the pseudo-SUL magnetized by the write field from the writer pole tip. The magnetic flux magnitude and full width at half maximum increased with an increasing write field. We observed a correspondence between an actual recording situation and the electron holography observation. View full abstract»

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  • Flying-Height Measurement With a Symmetrical Common-Path Heterodyne Interferometry Method

    Publication Year: 2010 , Page(s): 928 - 932
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (282 KB) |  | HTML iconHTML  

    To enhance the magnetic storage capacity of hard disk drives, the areal density of recording has to be increased continuously. But as the areal density of recording increases to over 100 Gb/in2, the head-disk physical gap, also called flying height (FH), decreases to less than 10 nm. Measurement of FH becomes a significant challenge. In this paper, we propose a symmetrical common-path heterodyne interferometry method to measure FH, utilizing a transverse mode Zeeman laser and a high-speed phase measurement technology, which has the sampling frequency of 100 kHz. We have developed a prototype FH tester based on the method. To effectively compensate influences of the tilt of the rotating disk, vibration of the optical system, and other environmental disturbances on measurement accuracy, we introduced a tri-spot distribution compensation method. Theoretical analysis indicates that the resolution of the FH measurement method reaches 0.1 nm. We carried out a series of experiments of FH measurement with this system, and the results indicate that the measurement system is sensitive enough to FH variation and can measure FH with a high precision and high response. We compared the experimental results with the predictions of FH by numerical simulation of thin-film gas lubrication of sliders, with good agreement. View full abstract»

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  • Improving Burst Error Tolerance of LDPC-Centric Coding Systems in Read Channel

    Publication Year: 2010 , Page(s): 933 - 941
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1093 KB) |  | HTML iconHTML  

    We report on the use of low-density parity check (LDPC)-centric error correction coding (ECC) for magnetic recording read channel in the presence of significant burst errors. Since an LDPC code by itself is severely vulnerable to burst errors due to its soft-decision probability-based decoding, we focus on LDPC-centric concatenated coding in which LDPC code is used as inner code. To improve the burst error tolerance, we propose a hybrid LDPC-centric concatenated coding strategy in which one inner LDPC codeword is replaced by another codeword with much stronger burst error correction capability. This special inner codeword reveals the burst error location information, which can be leveraged by the inner LDPC code decoding to largely improve the overall robustness to burst errors. Using a hybrid BCH-LDPC/RS concatenated coding system as a test vehicle, we demonstrate a significant performance advantage over its RS-only and LDPC-only counterparts in the presence of three different types of burst errors. View full abstract»

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  • Analysis of Eddy-Current Loss in End Shield and Frame of a Large Induction Machine

    Publication Year: 2010 , Page(s): 942 - 948
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (879 KB) |  | HTML iconHTML  

    This paper proposes an effective method of analyzing the eddy-current loss within the end shield and frame of an electric machine. The standard impedance boundary condition is applied to the conducting surfaces of complete 3-D models, and the models are solved by time-harmonic finite-element analyses. Measurement of the temperature rise is completed as a validation of the proposed method. The effect of the distances between the conducting surfaces and coil ends is studied by computing the eddy-current loss for a series of 3-D models having different distances. In addition, simplified 2-D models are used to study the influence of material nonlinearity. In brief, the proposed method is feasible in computing the eddy-current loss. The eddy-current loss within the regions close to the coil ends is larger than the other regions in the end shield and frame, but the total loss is quite small, compared, for instance, with the copper loss within the stator winding. Furthermore, the farther the end shield and frame are from the coil ends, the smaller the eddy-current loss is. Finally, it is found that the eddy-current loss is larger in the nonlinear case than in the linear case. View full abstract»

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  • Interdependence of Demagnetization, Loading, and Temperature Rise in a Permanent-Magnet Synchronous Motor

    Publication Year: 2010 , Page(s): 949 - 953
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    The demagnetization of permanent magnets in permanent-magnet machines has been under discussion in many publications lately. Demagnetization models have been used, for example, to optimize the machine structures but there have been no studies on how the demagnetization is coupled with the loading and temperature-rise of the machine and how this coupling should be modeled. In this paper, we model the dynamics of the demagnetization of a dovetail machine under a constant load torque. We show that the thermal model should be included in the demagnetization calculations. The demagnetization will cause an increase of the copper losses, which will increase the temperatures of the machine. This will cause more demagnetization and might lead even to a stall in a situation in which a model neglecting the thermal effects predicts stable operation without additional demagnetization. View full abstract»

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  • A Vector Control Method of LPMBDCM Considering Effects of PM Flux Linkage Harmonic and Cogging Force

    Publication Year: 2010 , Page(s): 954 - 959
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (570 KB) |  | HTML iconHTML  

    This paper presents a general vector control principle of surface-mounted permanent magnet (SPM) motors with arbitrary back-electromotive-force (back-EMF) waveform, then applies it to minimize the force pulsation of three-phase linear permanent magnet brushless dc motors (LPMBDCMs). The principle is derived from the force equation in the dot product form of the current vector and the permanent magnet (PM) flux linkage derivative vector. It indicates that the mutual force is proportional to the amplitude of current vector, and the ohmic loss is at the minimum when the current vector is aligned with the PM flux linkage derivative vector. Based on a d'q' asynchronously rotating reference frame considering the effects of PM flux linkage harmonic, a new id' = 0 vector control method with the cogging force compensation is proposed according to the principle. From the results of simulation with an accurate finite element (FE) based phase variable model, the validity of the proposed control method is verified compared with the conventional PWM current control for a LPMBDCM. View full abstract»

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  • Why we joined ... [advertisement]

    Publication Year: 2010 , Page(s): 960
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    Freely Available from IEEE
  • IEEE Magnetics Society Information

    Publication Year: 2010 , Page(s): C3
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    Freely Available from IEEE
  • IEEE Transactions on Magnetics institutional listings

    Publication Year: 2010 , 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