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Magnetics, IEEE Transactions on

Issue 4 • Date Jul 1991

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Displaying Results 1 - 25 of 28
  • Magnetostatic energy calculations

    Publication Year: 1991 , Page(s): 3539 - 3547
    Cited by:  Papers (9)
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    Magnetostatic self-energy can in principle be calculated by evaluating a certain sixfold integral, though this is not practical even for very simple cases. It is pointed out that some analytic transformation of this integral can facilitate computations, especially with an appropriate choice of Ritz models. A review of these is followed by a review of some of the methods that have been used for numerical evaluation of this energy term, in particular Brown's method of approaching the value by calculating rigorous upper and lower bounds. View full abstract»

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  • Magnetization process in Permalloy multilayer films

    Publication Year: 1991 , Page(s): 3579 - 3587
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    The magnetization process in positively coupled double and multilayered systems of Permalloy separated by carbon layers has been investigated. Domain patterns appearing in this process have been observed by both Lorentz electron microscopy and high-resolution Kerr effect. The patterns display a microstructure different from that observed in the single films, e.g., twin walls with crossing points, quasi-walls, superimposed cross and circular Bloch lines, and 360 degrees walls. The origin of the observed structures is analyzed. The effects of magnetic flux closure are shown. View full abstract»

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  • A resistor network theory of the giant magnetoresistance in magnetic superlattices

    Publication Year: 1991 , Page(s): 3548 - 3552
    Cited by:  Papers (3)
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    An explanation of the giant magnetoresistance effect observed in some magnetic superlattices is given in terms of an equivalent network of resistors. The model leads to a simple analytic formula that relates the magnetoresistance to the spin-dependent electron mean-free paths and thickness of the magnetic and nonmagnetic layers in the superlattice. The formula is used to study the giant magnetoresistance of Co/Cu and Fe/Cr superlattices, and is also used to predict the most favorable values of parameters for a large magnetoresistance effect. View full abstract»

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  • A mechanism of magnetic hysteresis in heterogeneous alloys

    Publication Year: 1991 , Page(s): 3475 - 3518
    Cited by:  Papers (207)
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    It is suggested that in many ferromagnetic materials there may occur particles distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible. For such single-domain particles, change of magnetization can take place only by rotation of the magnetization vector. As the field changes continuously, the resolved magnetization may change discontinuously at critical values of the field. The character of the magnetization curves depends on the degree of magnetic anisotropy of the particle and on the orientation of easy axes with respect to the field. The magnetic anisotropy may arise from the shape of the particle, from magnetocrystalline effects, and from strain. A detailed quantitative treatment is given of the effect of shape anisotropy when the particles have the form of ellipsoids of revolution, along with a less detailed treatment for the general ellipsoidal form. View full abstract»

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  • Investigation of coercive squareness in TbFeCo films

    Publication Year: 1991 , Page(s): 3690 - 3696
    Cited by:  Papers (1)
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    TbFeCo is one of the most promising magnetooptical recording media because it shows a high uniaxial anisotropy and a fairly good Kerr effect, and its composition can be tailored to achieve a large room temperature coercivity. A basic study was carried out to determine the factors affecting the mechanisms of magnetization reversal and the regularity of domain growth at room temperature in TbFeCo films. A technique has been established to quantify the regularity of domain growth in terms of coercive squareness. It has been observed that intrinsic magnetization and uniaxial anisotropy are the two most significant parameters to affect coercive squareness. Deposition processes and conditions have a very slight influence on coercive squareness. View full abstract»

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  • Giant magnetooptic rotations: the role of orbital polarization and explicit correlation effects

    Publication Year: 1991 , Page(s): 3648 - 3654
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    An ab initio itinerant-electron calculation for a class of cerium and uranium compounds was performed over the full frequency range studied experimentally. The band structure is obtained from a self-consistent spin-polarized full-potential linearized muffin-tin orbital calculation with a true interstitial. It was found that, for the compounds that display giant Kerr rotations, such a conventional calculation provides magnetooptic behavior very different from that obtained experimentally. This poor agreement was attributed to the presence of a large orbitally driven magnetism totally unlike the magnetism of Ni and Fe, and to the possible importance of explicit correlation effects on approaching heavy fermion behavior. Therefore, explicit orbital polarization was incorporated into the band calculation. This brings about a much better agreement for the ordered magnetic moments but fails to provide adequate agreement for the magnetooptic behavior; furthermore, unlike a calculation including explicit correlation effects, it does not provide agreement with the experimental ordered moment for the incipient heavy fermion CeTe system. View full abstract»

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  • The exchange-spring magnet: a new material principle for permanent magnets

    Publication Year: 1991 , Page(s): 3588 - 3560
    Cited by:  Papers (102)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1584 KB)  

    It is proposed that permanent magnets can be made of composite materials consisting of two suitably dispersed ferromagnetic and mutually exchange-coupled phases, one of which is hard magnetic in order to provide a high coercive field, while the other may be soft magnetic, just providing a high saturation Js, and should envelop the hard phase regions in order to prevent their corrosion. A general theoretical treatment of such systems shows that one may expect, besides a high energy product (BH)max, a reversible demagnetization curve (exchange-spring) and, in certain cases, an unusually high isotropic remanence ratio Br/Js, while the required volume fraction of the hard phase may be very low, on the order of 10%. The technological realization of such materials is shown to be based on the principle that all phases involved must emerge from a common metastable matrix phase in order to be crystallographically coherent and consequently magnetically exchange coupled. View full abstract»

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  • Anisotropy pinning of domain walls in a soft amorphous magnetic material

    Publication Year: 1991 , Page(s): 3678 - 3689
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2248 KB)  

    Ribbons were annealed in the demagnetized state with one wall along the ribbon middle. This wall becomes pinned during the heat treatment. Reentrant reversal occurs when reverse domains are nucleated at the ribbon edge with a threshold field larger than the demagnetizing field; this wall does not annihilate when it meets the pinned wall but leaves a line of reverse domains stabilized by ripple in the anisotropy. These domains permit a regular smooth reversal for the demagnetization process until the ribbon returns to the pinned configuration. The regular loop appears when the ribbon has been completely saturated by a large field. Mobile walls are nucleated on both sides of the pinned wall so that the ribbon does not return to the pinned configuration. Reversal now follows the usual demagnetization curve over the entire cycle. Kerr magnetooptical domain and domain wall observations are used in this investigation. All of the possible wall structures predicted by the model of asymmetric flux closed Bloch walls were identified. View full abstract»

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  • Effect of orienting fields on agglomeration in dilute dispersions of magnetic fine particles

    Publication Year: 1991 , Page(s): 3700 - 3703
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    Static light scattering was used to investigate dilute dispersions of fine gamma -Fe2O3 magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10-4 vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles. View full abstract»

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  • Fine particle high gradient magnetic entrapment

    Publication Year: 1991 , Page(s): 3655 - 3677
    Cited by:  Papers (4)
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    The entrapment of fine colloidal paramagnetic (and diamagnetic) particles at magnetic capture centers in the colloid is reviewed. The effect of thermal diffusion on the entrapment from a static colloid is examined in the 1-D and 2-D cases. The latter case allows prediction of captured volumes of colloidal particles. The interparticle effects due to the Helmholtz double-layer electrical interaction and the magnetic dipole-dipole interaction are introduced, and their effect on the 1-D theory is calculated and shown to be of importance. A theory that incorporates the double-layer effect into the 2-D case is presented, and its predicted effects upon the volume of captured particles is examined. The flow of the colloid is introduced, and a framework that allows fine particle capture to be included as a special case of normal size particle entrapment theory is suggested. A diagrammatic means of assessing the effects of thermal diffusion and interparticle effects on entrapment is described. View full abstract»

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  • Erich Peter Wohlfarth

    Publication Year: 1991 , Page(s): 3469 - 3474
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    First Page of the Article
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  • Existence of magnetization-dependent Preisach models

    Publication Year: 1991 , Page(s): 3697 - 3699
    Cited by:  Papers (18)
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    I. D. Mayergoyz (1986) has shown that the necessary and sufficient conditions for a hysteretic process can be described by a classical Preisach model are that it possesses the wiping-out property and the congruency property. Magnetization-dependent Preisach models also have the wiping-out property but do not possess the congruency property. The necessary and sufficient conditions for a process to be describable by either of two magnetization-dependent models, the product model and the moving model are presented. The identification problem for both of these models is also addressed. Both models require the wiping-out property, but the moving model requires the skew-congruency property, and the product model requires nonlinear congruency. View full abstract»

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  • Feasibility study of an electromagnetic thruster for ship propulsion

    Publication Year: 1991 , Page(s): 3735 - 3742
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    A comprehensive computational feasibility study is presented for an outer-type electromagnetic thruster intended for ship propulsion. A thruster previously presented in the literature is modeled in a way to keep computer power needed in reasonable limits despite wide coverage of the efficiency estimates. For this purpose a two-dimensional approach is adopted. It is also shown how to generalize the results to similar vessels by means of scaling. Water salinity and magnetic flux density generated by the coils are included in the scaling model. The results are presented in a way to make comparison with the conventional ship propeller straightforward. View full abstract»

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  • Quantitative evaluation of coupling factor and its application

    Publication Year: 1991 , Page(s): 3721 - 3730
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    A numerical analysis of the coupling factor k, its applicable examples, and new formulas are described. A formula of 'reflectivity gamma ' of the magnetic flux, i.e., the ratio of the induced flux to the incident flux in a secondary coil whose winding is closed or in a metal conductor, has been derived in the process of theorizing k. In its straightforward application to nondestructive inspection, the varying component K, behaving like a vector, in impedance of a sensor coil resulting from a metal, is analyzed from a somewhat different point of view, and the locus of K, according to the distance from a specimen with eddy currents, is approximately in a straight line. A gamma -diagram due to a superconductor in the intermediate state is presented as an experimental example of K. View full abstract»

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  • Magnetization structures in thin-film recording media

    Publication Year: 1991 , Page(s): 3553 - 3562
    Cited by:  Papers (7)  |  Patents (1)
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    A computer simulation study of magnetization configurations in planar isotropic thin-film recording media and their transient behavior during magnetization reversal is presented. Magnetization structures formed during magnetization reversal are characterized for various medium parameters. It is found that a reversed region nucleates by formation of a magnetization vortex. Multiple vortex formation yields elongated reverse domains in the applied field direction. Randomly oriented crystalline easy axes provide natural sites for vortex formation, which are facilitated by magnetostatic interactions. Intergranular exchange coupling significantly enhances vortex motion through which domains expand. Large-size domains occur in exchange coupled films. During a domain expansion, vortex-crosstie pairs can be generated and annihilated. Annihilation of vortices, vortex-crosstie pairs, or vortex-vortex pairs completes local magnetization reversal. View full abstract»

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  • Electromechanical railgun model

    Publication Year: 1991 , Page(s): 3731 - 3734
    Cited by:  Papers (3)
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    The electromechanical aspects of railgun motion are modeled analytically. A Lagrangian formulation is used to obtain the force and circuit equations, which are then solved for energy conservation and resistive flux decay. The resulting integral equation is solved for the barrel length as a measure of the launcher size and cost. The solution for a lossy railgun with multiple conductors (augmented case) is explained, and energy recovery is discussed. View full abstract»

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  • Dynamics of domains and walls in soft magnetic films

    Publication Year: 1991 , Page(s): 3532 - 3538
    Cited by:  Papers (3)
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    General equations are derived to describe the simultaneous nonuniform planar rotations of the magnetization vector and displacements of curved domain walls and their junctions in soft magnetic films. These equations take into account effects of exchange stiffness, magnetic anisotropy, external and either long- or short-range demagnetizing fields, wall energy, and dissipation. The case of a matched film pair using the capacitor or transmission-surface approximation for its short-range demagnetizing energy is considered. The theory is founded on energy and dissipation functionals including domain and wall terms. The constraint of wall-normal magnetization continuity across a domain wall is handled by a method of implementing d'Alembert's virtual work principle without introducing Lagrange multipliers. The result is a set of coupled equations expressing the dynamic torque balance at points inside domains, the wall-domain constraint due to wall-normal magnetization continuity, an additional boundary condition coupling domain magnetization and wall curves, and the wall velocity. View full abstract»

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  • Spin-glass behavior in a fine particle system

    Publication Year: 1991 , Page(s): 3570 - 3578
    Cited by:  Papers (2)
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    A study of the magnetic behavior characteristic of a spin-glass, which has been examined for systems of ultrafine particles, is reported. The results obtained support the suggestion of E. P. Wohlfarth (1977) that spin-glass effects could arise from the clustering of impurity spins in the host material into ferromagnetic rich clusters. All the results are explained on the basis of the Neel superparamagnetic (blocking) model. The results obtained show that the behavior of fine particle systems is similar to that of certain spin-glass alloys (e.g., Au/Fe alloys). This result supports the idea that spin-glass alloys can be interpreted on the basis of a blocking model. View full abstract»

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  • Recent development of thin film materials for magnetic heads

    Publication Year: 1991 , Page(s): 3640 - 3647
    Cited by:  Papers (7)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    Recent developments of soft magnetic film materials in the past decade are reviewed. Approximately 20 kinds of alloy systems with high saturation induction of more than 10 kG have been reported in the last decade, although there were only three conventional head materials: Mn-Zn ferrite, Permalloy, and Sendust. A particular focus of the review is nanocrystalline films and multilayer films. Also reviewed are improvements in single-layer homogeneous films of Fe, Fe-Si, Sendust, and Fe16N2. Almost all the materials reported are Fe-based alloys, and some alloys are nitrogen related: iron-nitride compounds or nitrogen-containing alpha -Fe or Sendust. View full abstract»

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  • Transient eddy current distribution in the shield of the passively compensated compulsator-air-core machines

    Publication Year: 1991 , Page(s): 3710 - 3720
    Cited by:  Papers (2)
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    The eddy current distribution in the shield of an air-core passively compensated pulsed alternator (compulsator) is discussed. The action of the shield reduces the inductance of the armature winding considerably, thus enabling it to deliver high-power pulse to low-impedance loads. By virtue of its function, the shield is stressed mechanically as well as thermally. An analytical solution of the 2-D diffusion and convective diffusion equations is obtained. The solution is obtained by the extraction of the poles and corresponding residues of the transformed equations. The theory was developed specifically for the shield of an air-core compulsator, which is a single-phase alternator. By using superposition, the results can also be applied to determine the transient eddy current distribution in the shield of superconducting synchronous generators. View full abstract»

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  • An analysis of the magnetic field of a ring head with a highly permeable underlayer

    Publication Year: 1991 , Page(s): 3751 - 3755
    Cited by:  Papers (8)
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    An idealized mathematical model of the magnetic field due to a ring head with a highly permeable underlayer is solved using Fourier analysis. Accurate Fourier coefficients are derived for a range of gap dimensions. The leading term of the resulting exact series is shown to be equivalent to a previously published approximation, but it is demonstrated that this term alone is not normally sufficient to predict the field accurately. View full abstract»

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  • Nonlinear eddy current effects in ferromagnetic materials in the presence of DC magnetic fields

    Publication Year: 1991 , Page(s): 3704 - 3709
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    Eddy current effects in nonlinear ferromagnetic materials in the presence of a supplementary DC magnetic field are analyzed. The analysis is for a one-dimensional configuration, a semi-infinite plate magnetized homogeneously in a direction parallel to its surface. The nonlinear magnetization characteristic of the ferromagnetic plate material is assumed to be of a step-function form. Solutions of the electric field intensity on the plate surface, the penetration depth of eddy currents in the plate, the eddy current losses, and surface impedance in the presence of a DC magnetic field are obtained. A connection is found between the values obtained in simultaneous DC and AC magnetization conditions and the values obtained in the case of only AC magnetic field excitation. View full abstract»

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  • A new theory of recording media noise

    Publication Year: 1991 , Page(s): 3519 - 3531
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1165 KB)  

    Previous investigations of the noise in particulate or grainy recording media have considered statistical variations in the processes by which the particles become magnetized. The theory of noise presented includes also statistical variations in the packing density of the particles. An extremely simple analysis shows that, when both of these phenomena are included properly, the noise power of recording media may always be expected to depend upon the magnetization, or signal level, and the particle packing factor. It is found that the recording media should always provide higher signal-to-noise ratios (SNRs) than was previously supposed. It is pointed out that the signal recovery or detection techniques employed today in magnetic storage devices cannot yield optimum SNRs or bit error rates. Some algebraic and/or conceptual errors in the published literature on noise are discussed. View full abstract»

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  • FMR and EXAFS modeling of heat-treated Fe-rich and Co-rich TM-M thin films

    Publication Year: 1991 , Page(s): 3620 - 3639
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1632 KB)  

    Ion-beam sputter-deposited alloy films of Co74Fe6B15Si5 and Fe75Ni5B15Si5 were examined for their magnetic and structural properties. Films were characterized by ferromagnetic resonance, vibrating sample magnetometry, and extended X-ray absorption fine structure (EXAFS) analysis. Using atomic parameters deduced from EXAFS modeling and fitting procedures, magnetic properties were calculated with no adjustable parameters. Correlation between perpendicular FMR measurements and EXAFS first-shell modeling suggests a low-temperature formation of cobalt-borides in the Co74Fe6B15Si5 alloy. Annealed Fe75Ni5B15Si5 samples did not display evidence of structural and/or magnetic instabilities until the onset of long-range crystallization near Tann=400 degrees C. View full abstract»

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  • Demagnetizing factors for cylinders

    Publication Year: 1991 , Page(s): 3601 - 3619
    Cited by:  Papers (67)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1536 KB)  

    Fluxmetric (ballistic) and magnetometric demagnetizing factors Nf and Nm for cylinders as functions of susceptibility chi and the ratio gamma of length to diameter have been evaluated. Using a one-dimensional model when gamma >or=10, Nf was calculated for -1m was calculated for chi to infinity . Using a two-dimensional model when 0.01m and Nf were calculated for -1f and Nm were computed exactly using inductance formulas. 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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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology