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Magnetics, IEEE Transactions on

Issue 4 • Date April 2012

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Displaying Results 1 - 25 of 116
  • [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): 1253 - 1261
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  • Soft Magnetic Materials 20 Conference Chair's Foreword

    Page(s): 1262
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  • Publication Chair's Preface

    Page(s): 1263 - 1264
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  • Soft Magnetic Materials 20 Conference

    Page(s): 1265
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  • Controlling the Domain Wall Dynamics by Induced Anisotropies

    Page(s): 1266 - 1268
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    Amorphous glass-coated microwires are magnetic materials well-known by very high domain wall velocities reaching up to 15 km/s. In the previous works was shown, that domain wall dynamics in microwires could be effectively tuned by biasing of additional anisotropies. Here we show the possibility of inducing anisotropy to the microwires. Thermal annealing at 300°C in perpendicular field speeds-up domain wall velocity from 1 km/s (as-cast state) to 6 km/s. On the other side, thermal annealing at the same temperature but without perpendicular field leads to the maximum domain wall velocity of about 4 km/s only. This underlines the importance of two perpendicular anisotropies on fast domain wall velocities in microwires. View full abstract»

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  • Magnetization Configurations in NiFe Slotted Rings Studied by Magneto-Optical Kerr Effect and Magnetic Force Microscopy

    Page(s): 1269 - 1272
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    The magnetization states and the reversal mechanisms of 30 nm thick NiFe full and slotted rings, with outer and inner diameter of 1400 nm and 600 nm, respectively, are analysed by magneto-optical Kerr effect and in-field magnetic force microscopy. The evolution of the magnetization configuration is investigated as a function of the applied field intensity. Both the measured hysteresis loops and the MFM images are satisfactorily reproduced by a combined micromagnetic and analytical approach, showing that the presence of the slot in one arm of the ring forces the system to undergo a transition into a flux closure vortex state of well defined chirality. Both the reversal mechanism and the field range where the vortex exists are influenced by the aperture angle of the slot. View full abstract»

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  • Influence of Plasticity on Magnetic and Magnetostrictive Behaviors of Dual-Phase Steel

    Page(s): 1273 - 1276
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    Magnetic and magnetostrictive behaviors of magnetic materials are very sensitive to mechanical stress and especially to plastic deformation. A model based on the decomposition of a plastified material into mechanically hard and soft phases has been proposed. An appropriate experimental procedure is presented in order to validate the model. The magnetic and magnetostrictive behaviors of a dual-phase steel are carried out. Measurements are made at unloaded stress and under various applied stress to observe a recovery phenomenon predicted by the modeling. Experiments and modeling are compared. View full abstract»

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  • Multidomain Modeling of the Influence of Plastic Deformation on the Magnetic Behavior

    Page(s): 1277 - 1280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (645 KB) |  | HTML iconHTML  

    Magnetic non destructive methods are frequently used in the industries of steel since magnetic behavior demonstrates a good sensitivity to the microstructural and/or mechanical changes. Magnetic behavior is especially sensitive to plastic straining that occurs for example with the manufacturing of materials (cutting, punching). Evaluating the state of a material from a measurement requires a modeling of the behaviors of the material (local constitutive laws) involved that must on the other hand demonstrate low computation time. Such magneto-mechanical modeling is proposed, based on the so-called multidomain model. View full abstract»

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  • Identification of Soft Magnetic B-H Characteristics Using Discrete Dynamic Preisach Model and Single Measured Hysteresis Loop

    Page(s): 1281 - 1284
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (279 KB) |  | HTML iconHTML  

    In this paper, the identification of soft magnetic B - H characteristics when using the single measured hysteresis loop and fitting the discrete dynamic Preisach (DDP) model is addressed. The magnetic measurements with primary and secondary windings are performed to obtain the magnetostatic system response. The constrained least-squares estimation of the Preisach density function yields the global solution even for limited hysteresis data. The uncertainties detected during the measurement and computation of B and H values are discussed. View full abstract»

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  • Nitrogen Vacancy and Magnetic Property in Cu-Doped AlN From First-Principles Calculations

    Page(s): 1285 - 1288
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    The effects on the ferromagnetism of a nitrogen defect in Cu-doped AlN with a Cu concentration of 2.77-8.33% have been investigated by first-principles. For AI0.9723Cu0.0277N, a global magnetic moment of 1.46 μB/cell with a localized magnetic moment of 0.75 μB/Cu is found. The formation of Cu-Cu in AlN with the N vacancy (VN) is more energetically favorable than that without the VN. Hence, the Cu + VN state is produced easily. The Cu magnetic moment of Cu-Cu pair becomes very low by the weak 3d-3d spin coupling due to the spin-exchange interaction between Cu-3d and N defect states. View full abstract»

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  • Fast Switching in Magnetic Tunnel Junctions With Two Pinned Layers: Micromagnetic Modeling

    Page(s): 1289 - 1292
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (727 KB) |  | HTML iconHTML  

    Spin transfer torque random access memory is one of the promising candidates for future universal memory. The reduction of the current density required for switching and the increase of the switching speed are the most important challenges in this area. In this paper, a penta-layer structure with two pinned magnetic layers is studied by means of extensive micromagnetic calculations. By numerically investigating the dynamics of the switching process, a methodology of how to achieve fast and symmetric switching without a compensating magnetic field is presented. Our simulations also highlight the importance of the field acting perpendicular to the plane, which facilitates switching. View full abstract»

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  • Effects of the Cu Doping on Critical Behavior of {\rm La}_{0.7}{\rm Ca}_{0.3}{\rm MnO}_{3}

    Page(s): 1293 - 1296
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    We have studied the influence of the Cu-doping on the critical properties of a polycrystalline sample of La0.7Ca0.3Mn0.95Cu0.05O3 prepared by solid-state reaction. Analyses of static magnetization data in the vicinity of the ferromagnetic-paramagnetic phase transition based on the modified Arrott plot reveal critical parameters of TC ≈ 197.3 K, β = 0.49 ± 0.03 and γ = 1.04 ± 0.04. These parameters are in good agreement with a magnetic equation of state M(H, ε) = εβf±(H/εβ+γ), where ε = (T - TC)/TC (the reduced temperature), f+ for T >; TC and f_ for T <; TC. Comparing with theoretical models, the critical exponents in our case are close to those expected for the mean-field theory. This reflects that the Cu doping leads to the second-order phase transition in La0.7Ca0.3Mn0.95Cu0.05O3 while the parent compound of La0.7Ca0.3MnO exhibits the first-order phase transition. Such the phenomenon is assigned to changes in structural parameters, Mn3+/Mn4+ ratio, and magnetic interaction mechanisms caused by Cu dopants. View full abstract»

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  • Vortex Induced by DC Current in a Circular Magnetic Spin Valve Nanopillar

    Page(s): 1297 - 1300
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    We investigate the characteristic of vortex states induced by a dc current in trilayer circular magnetic nanopillars experimentally. Our samples are designed such that both the soft and hard layers can contain a magnetic vortex and the interlayer is thick enough such that only dipolar interaction is important. The relative chiralities between the two layers' vortex configurations as functions of external field and current are studied with various diameters. We also perform micromagnetic simulation on the magnetization reversals to compare with the magnetoresistance (MR) curves measured at low current and with current induced magnetization states. The current induced magnetization behaviors due to the spin transfer torque effect and the additional Oersted field are clearly identified on the resistance behavior. View full abstract»

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  • Spin-Disorder and Non-Degenerate Energy States in Geometrically Frustrated Materials

    Page(s): 1301 - 1304
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    We have studied chalcogenide Ni1-xFexGa2S4, showing geometrical frustration effect. M-H curves at 4.2 K reveal that the disordered spins cannot be rotated completely along the direction of high external field of 5 T, since these spins are strongly constrained in the triangular lattice. HC increases with increasing Fe concentration, being consistent with the enhanced antiferromagnetic (AFM) spin-spin interactions and the suppressed spin-fluctuation due to the increase in freezing temperature Tf. The specific heat (CP/T) measurement do not show any phase transformation between 2 and 160 K and there is no clear indication of gap in the temperature dependent CP curve between 0 and 7 T, because the atomic short-range ordering of the strained spin in the geometrically frustrated triangular lattice exists at low temperature. Though typical geometrically frustrated magnet shows degeneracy, Mossbauer analysis at 4.2 K shows that 5D of 3d orbit in the samples studied here is splitted into 5T2g and 5E2g, and 5T2g is further splitted into singlet and doublet by large electric quadrupole splitting. This suggests that Fe2+ ionic state has no absolute degenerate energy states in all samples due to Jahn-Teller effect. View full abstract»

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  • Memory Effects in Ultra-Small CoFe _{2} O _{4} Nanoparticles

    Page(s): 1305 - 1308
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    We have employed the Monte Carlo (MC) simulation technique to study the aging effect on the Zero-Field-Cooled (ZFC) magnetization curves of ultra-small CoFe2O4 nanoparticles (mean size ~3 nm) embedded in a Si matrix. We consider spherical nanoparticles consisting of an ordered ferrimagnetic core and a ferrimagnetic disordered surface. The spins in the particles interact with nearest neighbors Heisenberg exchange interaction. Our simulations show that the spin-glass like disorder at the surface affects the magnetic properties to the extent that they exhibit aging effect: the low temperature ZFC magnetization depends on the time (waiting time, tW) spent before applying the magnetic field at a temperature at which most of the surface moments are frozen. The results of our MC simulations are in good agreement with the experimental findings confirming that the random freezing of surface spins is responsible for the aging effect. View full abstract»

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  • Magnetic After-Effect Analysis of Dislocation Relaxations in Thermally Aged and Neutron Irradiated Fe-Cu Alloys

    Page(s): 1309 - 1312
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (382 KB) |  | HTML iconHTML  

    Magnetic after-effect measurements of thermally aged and neutron irradiated, cold-worked Fe-Cu model alloys are performed in the temperature range between 100 K and 500 K in order to study the effects of copper precipitates and the irradiation induced defects on dislocation relaxation processes. For these two conditions, by increasing the level of plastic deformation, we show the clear difference in the behavior of dislocation related peaks. The effect of irradiation induced defects on dislocations is clearly pronounced by the increased number of relaxed dislocations compared to the number in the thermally aged samples. Furthermore, we observe a non-monotonic change in the behavior of the intensities of dislocation-related peaks in neutron irradiated samples, which occurs due to dislocation annihilation of the irradiation induced defects. View full abstract»

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  • Advancements in Magnetic Nanoparticle Reconstruction Using Sequential Activation of Excitation Coil Arrays Using Magnetorelaxometry

    Page(s): 1313 - 1316
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (921 KB) |  | HTML iconHTML  

    Magnetic nanoparticles can be employed for a broad range of biomedical applications where the knowledge of the distribution of the magnetic nanoparticles is of importance for efficacy, patient's safety, etc. The need exists to have an as accurate as possible quantification of the unknown particles distribution. Magnetorelaxometry (MRX) measurements are able to measure the magnetic induction originating from a certain distribution of magnetically activated nanoparticles. Starting from these measurements it is possible to determine the distribution using a minimum norm estimation technique. This approach is however ill-posed. We sequentially activate the magnetic nanoparticles through the use of excitation coil arrays with the aim to reduce the ill-posedness. This paper presents some advancements in magnetic nanoparticle reconstruction in terms of reconstruction quality using numerical simulations. The results show that inhomogeneous sequential activation is a proper alternative to homogeneous activation with Helmholtz coils since an increase in accuracy with a factor ranging from 1.5 until 2 is obtained. The presented numerical techniques coupled to MRX measurements can be of significant aid so to have more quantitative knowledge of the biodistribution. View full abstract»

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  • Suppression of Environmental Noise in Magnetopneumography by the Use of Higher Order Gradients

    Page(s): 1317 - 1319
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (510 KB) |  | HTML iconHTML  

    Magnetopneumography is a noninvasive method for examining contamination of metal workers' lungs by ferromagnetic dusts. Our aim is to estimate not only total amount but also spatial distribution of the dust. We use fluxgate magnetometer for measuring remanent field of contaminated volume (current experiments are mostly on phantoms). For earlier experiments we used a simple 6-channel magnetometer with improvised probe holder and we used multiple first order gradients. However, geometrical and other instabilities forced us to upgrade both the mechanical assembly and the fluxgate electronics. The environmental noise from relatively close sources is apparent even in first order gradients and thus - now with more stable electronics - we evaluated second order gradients in order to obtain a better signal. View full abstract»

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  • Size-Dependent Mechanisms in AC Magnetic Hyperthermia Response of Iron-Oxide Nanoparticles

    Page(s): 1320 - 1323
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB) |  | HTML iconHTML  

    This paper correlates the magnetic properties of iron-oxide nanoparticles in the size range 5-18 nm with the occurring heating loss mechanisms when magnetic nanoparticle colloidal suspensions are subjected to high-frequency ac magnetic fields. The narrow size distribution of the nanoparticles enabled their clear classification into: 1) the superparamagnetic region (as large as 10 nm) where heating is mainly attributed to Neel relaxation; 2) the intermediate superparamagnetic-ferromagnetic transition region (10-13 nm); and 3) the ferromagnetic region (above 13 nm) where hysteresis losses dominate. The results from specific loss power measurements suggest that for size and concentration optimization, superparamagnetic nanoparticles may release significant amounts of heat to the surroundings, while the hysteresis losses mechanism appears to be much more efficient and the heat transfer provided through may be easier tuned for magnetically driven hyperthermia applications. View full abstract»

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  • Magnetoelastic Effects and Distribution of Defects in Micrometric Amorphous Wires

    Page(s): 1324 - 1326
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    The influence of defects and the magnetoelastic anisotropy term on the domain wall dynamics of glass-coated amorphous microwires is investigated. Using modified Sixtus-Tonks set-up, we have determined the position of the domain nucleation and measured the magnetic field dependence of the domain wall velocity. We found that both internal and applied stresses significantly affect the domain wall dynamics especially for wires with reduced magnetostriction. Particularly, we conclude that the non-linear relationship between the do- main wall velocity and magnetic field is correlated with the existence of defects which act as nucleation centers of additional domains. View full abstract»

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  • Optimum Regime of Heat Treatment of Soft Magnetic Amorphous Materials

    Page(s): 1327 - 1330
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    The influence of Fe72.5Cu1Nb2Mo1.5Si14B9 nanocrystalline alloy annealing temperature on the structure and magnetic properties has been investigated. The heat treatment temperature of nanocrystalline soft magnetic alloy Fer2.5Cu1Nb2 Mo1.5Si14B9, which allows reaching the maximum value of the initial magnetic permeability, was found to be 15-20° higher than that ensuring the minimum coercive force. The relation between the numerical values of the coercive force, the initial magnetic permeability and the magnetic hysteresis loop rectangularity factor allows optimizing the mode of nanocrystalline alloy heat treatment. View full abstract»

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  • Nanocrystalline Soft Magnetic Fe-Si-B-P-Cu Alloys With High B of 1.8–1.9T Contributable to Energy Saving

    Page(s): 1331 - 1335
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1302 KB) |  | HTML iconHTML  

    Melt-spun Fe85Si1-2B8-11P1-4Cu1 alloys have unusual hetro-amorphous structures which can transform to nanocrystalline structures composed of α-Fe grains with less than about 25 nm in size with crystallization. Especially, Fe85Si1-2B8-11P1-4Cu1 nanocrystalline soft magnetic alloys prepared by crystallizing an as-quenched nanohetero-amorphous phase including a large amount of extremely small α-Fe grains (less than 2-3 nm in size) exhibit high-B800 of 1.8-1.9 T (at 800 A/m) almost comparable to those of commercial oriented silicon steels and significantly higher than those of non-oriented silicon steels, along with extremely low core loss (W) which is 1/2-1/3 smaller than that of the highest-grade oriented silicon steel and about one-order smaller than those of non-oriented silicon steels at maximum flux density of 1.7 T. The nanocrystalline alloys with lower materials cost due to absence of rare-metals are expected to not only contribute to significant energy-saving and reduction of CO2 emission through reduction in W but also be useful to conserve the earth's resources and environment. View full abstract»

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  • Structural and Magnetic Properties of FeCuNbSiB Thin Films Deposited by HiPIMS

    Page(s): 1336 - 1339
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    Using high-power impulse magnetron sputtering (HiPIMS) technique, Fe73.5Cu1Nb3Si15.5B7 thin films with thickness between 40 and 700 nm were deposited. The influence of deposition conditions (deposition time and argon pressure) and of the annealing temperature on the structure and coercive magnetic field of the magnetic films was analyzed. In the as-deposited state, the coercive magnetic field presents a minimum at about 10 mtorr argon pressure. The X-ray diffraction studies show that in the as-deposited state, the samples are amorphous, while after annealing at temperatures between 400°C to 525°C, α-Fe(Si) grains start to nucleate, the grain size varying from 2 to 18 nm. The Curie temperature of as-deposited amorphous phase and the onset of the primary crystallization are 355°C and 460°C, respectively. The lowest coercive magnetic field was obtained after annealing at 475°C. 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