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Magnetics, IEEE Transactions on

Issue 4 • Date December 1973

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Displaying Results 1 - 25 of 29
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Magnetic domain wall dislocation analogy and intrinsic coercivity

    Page(s): 602 - 606
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    A close analogy is shown to exist between a discrete crystal model of a magnetic domain wall and the Frenkel-Kontorowa model for crystal dislocations. It is used here for a simple calculation of the intrinsic coercivity (that due solely to the discrete character of the crystal lattice) of a 180° wall in an otherwise perfect crystal. On a purely continuum level, the analogy between dislocations and domain walls as two types of mobile crystal defects has been stressed by Akulov [1]. As will be seen in the present paper, the analogy extends to the atomistic level and a simple discrete model of a domain wall leads to difference equations which are similar to those of the Frenkel-Kontorowa model [2] for a dislocation. Some of the analytical experience and physical insight gained in the treatment of the latter problem, therefore, can be transferred to the magnetic case. As an example we reexamine in the light of this analogy the concept recently introduced by van den Broek and Zijlstra [3] of intrinsic coercivity due to the discrete nature of the crystal lattice. To understand the nature of this concept consider the following idealized situation: an infinite crystal contains a single planar 180° magnetic domain wall and no other defects. From a continuum quasi-static viewpoint this wall would be perfectly mobile, moving freely (even in the absence of thermal or zero-point motion) under an arbitrarily small applied magnetic field. However, if one adopts a discrete, atomistic viewpoint, then two equivalent equilibrium domain wall configurations which differ only by the displacement through one lattice parameter will be separated by a small energy barrier and a nonzero applied magnetic field Hcwill be required to move it. This situation is completely analogous in crystal dislocation theory to the concept of the Peierls stress, which is defined as the stress required to move a straight dislocation, quasi-statically, from one equilibrium position to an adjacent equilibrium position in the absence of other defects and without the aid of thermal or zero-point motion. Its calculation also requires a model which includes the discrete character of the crystal; a purely continuum calculation leads to a zero Peierls stress. In - fact, because of the close analogy, it might be desirable to use the term Peierls field for the critical applied field strength Hcsince this term so clearly conveys the concept, at least to those familiar with dislocation theory. The general nature of the model of a 180° domain wall is similar to that employed by van den Broek and Zijlstra [3]. View full abstract»

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  • The magnetostriction of rare-earth garnets containing gallium and europium: Old theory for new problems

    Page(s): 606 - 609
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    A calculation is made of the effect of gallium substitution upon the magnetostriction of rare-earth garnets, a problem of some interest because of the use of gallium substituted garnets as bubble-domain materials. The gallium alters the contribution to magnetostriction of the iron lattices by simple dilution and of the rare-earth lattice by reducing the exchange field acting upon the rare-earth ions. Site preference considerations must be included in the calculation. Expressions are produced for predicting the effect upon the magnetostriction constants of gallium substitution into a typical rare-earth garnet. The special case of EuIG is treated separately. Since the contribution to magnetostriction of the Eu3+ions depends on the square of the exchange field, EuIG is more strongly affected by Ga substitution than most garnets. View full abstract»

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  • Domain wall velocity and interrupted pulse experiments

    Page(s): 609 - 613
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    The velocity of magnetic domain walls in Bloch wall Permalloy thin films excited by interrupted easy axis drive fields is investigated and correlated with the available theory of transient wall contraction. The experimental technique is useful in determining the average wall velocity, and by comparing the velocity-field curves with field duration as a parameter it is possible to infer several features of the transient behavior. It is found that, when the displacement of the wall is of the order of a characteristic distance associated with the wall coercive force interaction, the threshold field for net motion as well as the mobility of the average velocity curves depend on the field duration. The theory together with a breakable-spring model of the coercive force interaction reasonably explain the observed phenomena. View full abstract»

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  • Influence of an in-plane magnetic field on the domain-wall velocity in Ga: YIG films

    Page(s): 614 - 616
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    Results are reported of an investigation on the velocity of a single straight magnetic domain wall in a Ga:YIG film as a function of the drive field and of a static magnetic field applied perpendicular to the wall in the plane of the film. At all drive fields a substantial increase of the wall velocity was observed when the in-plane field was applied. At an in-plane field of about 400 Oe and at a rather low drive field (2.4 Oe above the coercive field) a maximum value in wall velocity of 270 ms-1was observed. At higher drive fields the wall velocity decreased to a constant value of 110 ms-1, independent of the drive field. This behavior can be explained by extending Slonczewski's theory of domain wall motion to the present case. From the observed wall mobility parameter we have calculated the reduced Landau-Lifshitz damping constantlambda/gamma^{2}(3.7 times 10^{-9}Oe2s). This value is near to the value obtained by Spencer and LeCraw from linewidth measurements in FMR on Ga:YIG spheres (5 times 10^{-10}Oe2s). View full abstract»

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  • Domain formation and associated wall states

    Page(s): 617 - 621
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    Generation of Bloch lines in closed domains is examined on the premise that the magnetization remains continuous at all times. The model predicts the creation of two nonunwinding lines during the formation of each domain. Precession of the wall magnetization generates trains of unwinding lines. If such a domain is split while in a comb-like configuration, the resulting walls may contain large numbers of nonunwinding lines. Conclusions are verified experimentally by determining the number and handedness of lines in domains formed under different conditions. View full abstract»

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  • On the radial mode in bubble lattices

    Page(s): 621 - 624
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    The radial mode resonance frequency and quality factor behavior in general bubble lattices is studied. Results of direct calculations for the triangular lattice withl/z = 0.25are given and discussed in connection with the findings of Kaczér and Tomás. An alternative scheme allowing a calculation of the reduced frequency and quality factor on the basis of the static bubble radius field-dependence is also shown. Finally, an estimate is made of the expected frequencies and quality factors in a representative material. View full abstract»

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  • Magnetic properties of cobalt rare-earth thin films

    Page(s): 627 - 631
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    This paper describes the magnetic properties of dc sputtered thin films of Co-Gd and Co-Sm in various compositions. Magnetic moment density, hysteresis loop coercivity and squareness, and rotational hysteresis loss measurements are reported. Crystallite and domain sizes were observed with an electron microscope for a few compositions. A tentative model of magnetization reversal is proposed for some of the compositions. View full abstract»

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  • Hysteresis properties of sintered Sm Co5permanent magnets

    Page(s): 631 - 635
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    The magnetic properties of individual SmCo5particles have been extensively studied in the literature. In the present work, initial magnetization curves and hysteresis loops of sintered SmCo5magnets have been drawn with a hysteresigraph. The observed properties depend on the previous magnetic treatment of the sample. After thermal demagnetization, the initial susceptibility is very high; after dc field demagnetization, it is very weak. The inner hysteresis loops are often unsymmetrical. Results are interpreted by considering the magnets as particle assemblies related together by dipolar interactions. View full abstract»

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  • Magnetic and magnetostrictive properties of cube textured nickel for magnetostrictive transducer applications

    Page(s): 636 - 640
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    Magnetic and magnetostrictive properties of {100} <100> textured, polycrystalline nickel sheet have been measured in the <100> direction and compared with a randomly oriented nickel sheet. The {100} <100> textured nickel produced a 51 percent increase in the available magnetostrictive strain energy along with a 21 percent decrease in sound velocity. These improved characteristics when combined with an equivalent electromechanical coupling coefficient and a nearly linear response of magnetostrictive strain to the applied magnetic field, make "cube" textured nickel sheet an attractive new material for many transducer applications. View full abstract»

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  • Measurements of spectra of clustered Barkhausen transitions in technical steel

    Page(s): 641 - 646
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    Various measurements are performed to investigate the spectra of clustered Barkhausen transitions in technical steel. These spectra are formed by the discontinuous jumps of magnetization in the material, when the external magnetic field is changed with relatively high speed. The methods used include power, amplitude and autocorrelation spectra and their magnetization and temperature dependences. A differential correlation is shown to exist between the optically measured grain size and the different spectra, thus confirming the basic principle of a recently proposed electronic differential grain-size analyzer for technical steel. View full abstract»

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  • Influence of dislocation on magnetic domains in plastically deformed 3% Si-Fe

    Page(s): 647 - 650
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    Characteristic layer-like magnetic domains are observed on many large crystals of a polycrystalline bioriented type View full abstract»

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  • Measurement of rotating flux in silicon iron laminations

    Page(s): 651 - 654
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    A method of calculating the magnitude and direction of the instantaneous flux density in a thin lamination of magnetic material is described. The technique was demonstrated by measuring the rotating flux in samples of mild steel, grain-oriented silicon iron, and at a point in the T-joint of a three-phase, three-limbed transformer core. The flux in the mild steel sample was found to rotate at a constant angular velocity and to be constant in magnitude. In the silicon iron sample, and at a point in the T-joint, the flux density varied both in angular velocity and magnitude. A large 150 Hz component of rotational flux was found to cause high localized power loss in the T-joint. The power loss was measured using the "initial rate of rise of temperature method" and was compared with the predicted rotational hysteresis loss. View full abstract»

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  • The spatial variation of localized power loss in two practical transformer T-joints

    Page(s): 655 - 659
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    The power loss and flux distribution in two commercial T-joints have been compared. The simple 45°-90° T-joint and the slightly more complex 45° offset T-joint were chosen for the investigation, as they are the most common joints currently used in power transformers. The localized and overall power loss of each joint was measured using now-established techniques. Each joint was built in turn into a three-limb, three-phase core, employing 15-cm wide, 0.03-cm-thick 3.2% grain-oriented silicon iron laminations. The cores were magnetized at the same overall flux densities. The localized flux distribution in individual laminations in the joints were related to the localized loss variation. Rotational flux was found to occur in both joints and it caused areas of high localized loss. A combination of normal flux between adjacent layers of laminations, rotating flux, and circulating 3rd-harmonic fluxes caused the localized loss to rise to double the average core loss in some regions of the T-joints. For the 15-cm-wide laminations used, the 45° offset joint was 10% more efficient than the 45°-90° T-joint at a flux density of 1.6 T; the mean loss of both joints was more than 25% higher than the loss in the yokes and limbs. View full abstract»

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  • Stripe-domain dynamics in bubble-domain circuits

    Page(s): 660 - 663
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    It is widely known that bubble domains can exist when the bias field is between the elliptic instability (runout) field Heand the bubble collapse field Hbc. Values for Heand Hbcwere calculated by Thiele. It is not widely recognized that long stripe domains can also exist in the bottom 20% of this range. Stripes are stable up to the "stripe contraction" field, Hsc, which is about 0.02 M/μ0above Hefor thickness over intrinsic length,h/l, values from 4 to 10. (Hbcis about 0.10 M/μ0above He.) Values for Hscwere calculated by Kooy and Enz of Philips Research Labs. in 1960, although the importance of their result to bubble-domain devices was not apparent at the time. The velocity of the domain tip during stripout and contraction such as occurs during domain detection or transfer is important for calculating maximum circuit speeds. This is given byV = cG (H-H_{sc}), whereHis the field (bias field plus local field from currents or Permalloy elements),Gis the wall mobility, andcis a constant approximately equal to 0.5. View full abstract»

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  • Magnetic bubble-domain detection: Review and outlook

    Page(s): 663 - 669
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    This paper reviews the early work on the detection of magnetic bubble domains, as well as summarizing and comparing the most recent results. Topics include InSb sensors, Permalloy sensors (thick-film as well as thin-film), and bubble stretching techniques. The limitations on sensor input power imposed by heat dissipation and other factors are discussed. The relationship between bubble size and sense signal is then examined. Finally, projections are made for the detection of submicron bubble domains. View full abstract»

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  • The propagation of magnetic bubbles on permalloy disks

    Page(s): 670 - 673
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    A magnetic bubble generator consisting of a Permalloy disk and a current conductor loop has been used recently in a mass memory design utilizing magnetic bubble technology. The bias field range in which the disk can hold the seed bubble is measured in this report as a function of of the rotating field frequency. Above a critical frequency fc, the bias field margins begin to decrease. The dependence of fcon disk size is obtained for disks with diameters from 16 μm up to 43 μm at rotating fields of 20 and 30 Oe. The separation between Permalloy disks and the garnet film is kept at 0.8 μm or 1.6 μm. Results show that at a fixed rotating field, a smaller disk is preferable at higher frequency for a magnetic bubble material with a given mobility. The critical frequency fcobtained is in good agreement with a theoretical calculation using the viscous damping model by Rossol et al. For frequencies below fc, the bias field margin on the disk is equal to that of the propagating channel and circuit failure due to the loss of the generator seed bubble can be eliminated. View full abstract»

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  • Techniques for the measurement of air-bearing separation -- A review

    Page(s): 673 - 677
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    Various techniques for the measurement of air-bearing separation are described. Examples are given in the specific area of self-acting air-bearing sliders on rotating disks. The techniques can be categorized as capacitive, inductive and optical. The optical technique lacks frequency response but can provide an accurate and convenient way of calibration for the typically nonlinear but versatile capacitive and inductive gap sensors. View full abstract»

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  • One-sided fluxes -- A magnetic curiosity?

    Page(s): 678 - 682
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    It is shown that a previously unknown class of magnetization patterns exists in planar structures which have the unique property that all the flux escapes from one surface with none leaving the other side. A simple case is a constant amplitude rotating vector magnetization where the sense of rotation dictates which surface has no flux. More complicated magnetization patterns are elucidated. The likelihood that the one-sided flux phenomenon occurs partially in the normal write, the contact-printing and the print-through processes of tape recording is discussed. It is concluded that significant improvements in tape recording performance would ensue if means could be found to enhance the effect. View full abstract»

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  • Experimental and theoretical investigation of head to tape separation in magnetic recordings

    Page(s): 683 - 688
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    Although the mathematical model of a tape traveling over a cylinder (foil bearing) has been shown experimentally to be valid for a closely similar physical model, its application to predict separation between a tape and a magnetic head has shown large discrepancies. In this work, a modified model of a foil bearing, taking into account some details of the particular geometry of magnetic heads, is used to predict separation and to compare it to experimental results. As a result, the gap between theory and experiment is narrowed down considerably. View full abstract»

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  • Fourier synthesis of digital recording waveforms

    Page(s): 689 - 697
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    A digital recording system is modeled by means of a complex Fourier series representation employing transforms of arctangent functions to describe the effects of write field gradient demagnetization and self-demagnetization. Pulse asymmetry and rise time effects are incorporated by means of phase shifts from complex transfer functions used in describing the dependence of head properties on a complex permeability. Experimental measurements on a specific system (Co substituted γ-Fe2O3tape and metal heads) show good correlation with the theory, especially with respect to spectral content, waveform shape, and peak shifts. The model is one-dimensional and limited to recording media initially ac demagnetized and to a write current range in which it is possible to define an effective penetration depth for saturation recording. View full abstract»

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  • The reading characteristics of a finite length pole piece recording head

    Page(s): 698 - 699
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    The frequency response of a finite-length pole piece recording head is calculated numerically for various gap-to-pole-length ratios as well as for differing head-to-medium separations for an idealized sinusoidal magnetization distribution by application of the Cooley-Tukey fast Fourier transform. View full abstract»

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  • Laser recording on MnBi films

    Page(s): 700 - 704
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    The results of laser recording experiments in which a magnetic field controls the magnetization distribution along Curie-point switched micron-wide tracks are described. These experiments showed that analog as well as digital information may be recorded in this manner. 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