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Magnetics, IEEE Transactions on

Issue 4 • Date December 1970

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Displaying Results 1 - 25 of 26
  • [Front cover and table of contents]

    Publication Year: 1970 , Page(s): 0
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    Freely Available from IEEE
  • A model of magnetostriction interaction in thin double-layer magnetic films of Ni-Fe alloy

    Publication Year: 1970 , Page(s): 766 - 768
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    Under the assumption that in a double-layer film both layers are equally deformed, the following formula for the magnetostriction energy E = K_{c} \sin^{2} \alpha has been derived where K_{c} = (9/40)(2U'U is the coupling constant and α is the angle between the magnetization vectors. This formula is valid if we can neglect interaction with the substrate. The sign of the coupling constant is discussed. It turns out that where the composition of the two layers are different, the value of Kccan be, in some special cases, negative. View full abstract»

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  • Electron microscopy on high-coercive-force Co-Cr composite films

    Publication Year: 1970 , Page(s): 768 - 773
    Cited by:  Papers (44)  |  Patents (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1088 KB)  

    Electron microscopy was used to analyze the crystallographic and magnetic structures of high-coercive-force Co-Cr composite films. The chromium sublayer appears to give high coercive forces by causing the growth of cobalt in the hexagonal phase with a relatively narrow distribution of grain sizes. Magnetization reversal was examined by Lorentz microscopy of films with coercive fields up to H_{c} = 900 Oe. It proceeds by nucleation and extension of magnetostatically coupled domains. The progressive limitation of these extensions as the coercive force increases illustrates the connection between the magnetostatic coupling, the coercive force, and the squareness of the hysteresis loop. Lorentz microscopy was also used to investigate a recorded transition between NRZ 1 and 0 states and showed a saw-toothed structure, characteristic of a magnetization in the plane of the film. View full abstract»

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  • 0.25 × 106bit/in2NDRO coupled film memory elements

    Publication Year: 1970 , Page(s): 774 - 778
    Cited by:  Papers (5)
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    The fabrication and operation of high-density (0.25 × 106bit/in2) nondestructive readout (NDRO) memory elements are described. The high density is made possible by coupled films and Permalloy keeper. The NDRO is made possible by multiple-pulse WRITE or hard-direction bias field. Typical performance parameters are I_{w} = 60 mA, I_{b} = 30 mA, and V_{s} = 150 μV/3 ns. The small signal is detectable by multiple-pulse READ. When such memory elements are to be fabricated with peripheral circuits on the same Si chip, a self-contained chip will be obtained. Such chips could enjoy the same advantages as semiconductor memory chips such as few leads, modularity, amenability to bit organization, and possibility for error-correction, but would be capable of higher storage density due to simpler planar configuration. View full abstract»

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  • Signal sensing and magnetic film memory array design

    Publication Year: 1970 , Page(s): 778 - 784
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    A signal-to-noise analysis is presented to show its influence on the design of magnetic film memory arrays. The device geometry and array dimensions are varied independently to find the design limits within which reliable signal detection can be performed, that is, the range within which adequate signal-to-noise ratio is obtained at the sense amplifier. The result is a plot of the required number of READ pulses for any combination of line width and line length in the range of interest. Line widths between 1/2- and 4-Mil and array sizes up to 4096 × 4096 bits were investigated. Multipulse readout is required for line widths less than 1.5-mils. A 256 × 256 array of 1/2-mil lines on 1-mil centers requires 12 signal pulses of 3-ns duration each, whereas a 1024 × 1024 array of 1-mil lines on 2-mil centers requires 7 signal pulses. It should be noted that in addition to adequate signal-to-noise ratio, a minimum of signal is needed (not obtainable through multiple READs) commensurate with the gain of the sense amplifier. These considerations are all combined in a set of design curves which can be used to make design tradeoffs between device size, array size, and cycle time. View full abstract»

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  • Stress relief mechanism of aging in plated-wire memories

    Publication Year: 1970 , Page(s): 785 - 789
    Cited by:  Papers (2)
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    Results are presented which identify a dominant aging mechanism of plated-wire memory elements in the absence of magnetic fields. This mechanism, i.e., stress relief in the Permalloy film, can occur even in elements stabilized against field-induced aging. The evidence for stress relief consists of aging and strain sensitivity measurements on samples of different Permalloy composition. In aging experiments under vacuum at 230°C, Ni-rich films show an increase in anisotropy field Hk, while Fe-rich films show a decrease. A stress relief model is described which relates such aging changes to the initial film stress the cylindrical geometry, and the tension strain sensitivity. Using this model, agreement is found between film stress deduced from the Hkaging changes, and film stress from direct measurements, reported in the literature. Films which are judged to have zeromagnetostrictive composition (ZMC) on the basis of torsion sensitivity are found to show nonzero tension sensitivity. This is satisfactorily accounted for by circumferential composition inhomogeneity, which is shown analytically to explain the observed decrease in anisotropy field with tension. It is concluded that reduction of such inhomogeneity by appropriate deposition techniques is favorable to both smaller strain sensitivity and increased aging stability. View full abstract»

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  • Magnetoelastic effect in thin magnetic films at parametric excitation

    Publication Year: 1970 , Page(s): 789 - 791
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    The bending oscillations of the film-substrate system, explained by magnetostriction interaction, were observed at parametric excitation of thin magnetic films at the frequency 11 MHz. The frequency of the bending oscillations changed from 104to 105Hz. The dependences of the elastic modes on dc and HF magnetic fields affecting the film have been investigated. Some advice for the technical applications of the observed phenomenon is given in this paper. View full abstract»

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  • Core memories: The perennial leader

    Publication Year: 1970 , Page(s): 791 - 795
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    An historical survey of the memory industry is given, and the progress of the ferrite core memory since it was first introduced is examined. It is shown that the computer industry could not have developed without a reliable and relatively cheap storage element capable of being produced in great quantity. The core memory satisfied this requirement but appeared to be vulnerable to competition by technologies more suited to mass production. The reasons why core memories have not been supplanted are examined, and a forecast for the next ten years is presented. The prediction is that core memories will retain the largest share of dollar-volume in on-line memory industry for the duration of this period. View full abstract»

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  • Formation and magnetic properties of ultrafine spinel ferrites

    Publication Year: 1970 , Page(s): 795 - 799
    Cited by:  Papers (2)
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    Investigations of the formation and magnetic properties of MnδCo1-δFe2O4formed in alkaline aqueous solution by the coprecipitation method are covered. The lattice constant of these ferrites apparently reduced with decreasing average particle size below about 500 Å. The coercive force ratio of MnFe2O4and Co-Fe2O4is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K1of sintered ferrites. As the average particle size became larger, the coercive force and the apparent remanence increased linearly, and superparamagnetic critical size was determined. The sizes range, for example, from 50 to 100 Å for CoFe2O4and from 150 to 200 Å. for MnFe2O4. From the correlation between the average particle size and their magnetization, the limit size of ferromagnetic critical particle was also determined. Results obtained in this experiment are approximately in accord with Néel's Version of the theory on thermal fluctuation aftereffect of magnetic fine particles. View full abstract»

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  • Statistical characterization of polycrystalline ferrite media

    Publication Year: 1970 , Page(s): 800 - 803
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    The classical field theory superposition principle, the central limit theorem, and the gyromagnetic equations of motion are invoked as a basis to formulate a quasi-static statistical model for polycrystalline ferrite media with Gaussian statistics. The use of this model to analyze small signal reversible rotational phenomena is illustrated. It is also demonstrated that this model and a previous microwave model given by the authors are maximum entropy models An analogy between the maximum entropy property of these models and the Gibbs thermodynamic equivalence for equilibrium and a state of maximum entropy is noted. View full abstract»

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  • Effect of interaction on magnetic properties of a particulate medium

    Publication Year: 1970 , Page(s): 804 - 808
    Cited by:  Papers (4)
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    Samples of magnetic particles were prepared in dry powder form, as well as in a plastic binder system. Magnetic measurements were made on the samples as function of the volumetric packing factor. Coercive force Hc, squareness, and anhysteretic magnetization measurements are correlated with the uniformity of particle dispersion. It was found that the behavior of Hc, squareness, and the initial anhysteretic susceptibility as a function of the packing factor are good indications of the degree of dispersion of the particles. It is shown that if the particles are well dispersed, Hcincreased with increased dilution, and the initial anhysteretic susceptibility increased at both high and low dilutions. A mathematical model is developed to explain the observed results. The model consists of a double distribution of interaction fields to account for the well-dispersed and the agglomerated particles. View full abstract»

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  • Accidental printing effect of magnetic recording tapes using ultrafine particles of acicular γ-Fe2O3

    Publication Year: 1970 , Page(s): 808 - 811
    Cited by:  Papers (6)
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    Five kinds of acicular γ-Fe2O3powder of which axial length varies from 0.17 to 0.80 μm with almost the same axial ratio are manufactured. The variance of coercive force and printing effect as the average axial length of the particles varies is shown. Coercive force of which particle axial length is about 0.35 μm shows maximum value. The printing effect increases according to the decrease of axial length. The printing effect increases with contacting time. The temperature dependence of coercive force and remanent magnetization are measured from 25 to 200°C. These two properties decrease as the temperature increases, but the decreasing inclination becomes steeper as the axial length is smaller. The relationship between the printing effect and the decreasing inclination of coercive force is nearly linear. From the temperature dependence of the printing effect, the activation energy of the printing effect can be calculated. The activation energy of the smallest particle is about 0.05 eV and the others are about 0.15 eV. This measured activation energy is discussed in connection with the relaxation equation. View full abstract»

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  • Characteristics of the readback signal in digital magnetic recording

    Publication Year: 1970 , Page(s): 811 - 817
    Cited by:  Papers (6)
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    A theoretical treatment for the readback process in digital magnetic recording is presented. Three major factors, namely, the medium constant s which defines the extent of the surface charge density, the head-to-medium spacing d , and the read head gap 2 g, are taken into consideration. A general solution giving the characteristics of pulse readback signal is shown as a function of s,d and g . Both amplitude and pulse width of the readback signal are arranged as a product of the medium loss, spacing loss, and gap loss, making it easy to describe the influence of each factor separately. The final value of the amplitude and the pulse width is proportional to that of the recorded surface charge density. Spacing loss simply depends on the ratio of d/s ; gap loss depends on the ratio of g/(s + d) . Theoretical results are compared with experiments which show good agreement for a wide combination of s,d , and g . View full abstract»

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  • Offset and noise in fluxgate magnetometers

    Publication Year: 1970 , Page(s): 818
    Cited by:  Papers (3)
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    First Page of the Article
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  • Temperature compensation of fluxgate magnetometers

    Publication Year: 1970 , Page(s): 819 - 822
    Cited by:  Papers (1)
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    Based on the finding that the temperature dependence of fluxgate sensors is proportional to the measured field, a temperature compensation circuit is described using the copper resistance of the fluxgate secondary winding as the thermosensitive part of a bridge. The bridge voltage is derived from the magnetometer output so the compensation is only active in high fields. View full abstract»

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  • Pressures on cylindrical magnetic domain walls

    Publication Year: 1970 , Page(s): 822 - 827
    Cited by:  Papers (4)
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    The pressures on cylindrical magnetic domain walls are discussed with particular emphasis on bubbles, that is, near-circular domains. In the case of anisotropic wall energy, bubbles will be slightly elliptical, and a formula is derived relating the ellipticity to the anisotropic wall energy. Various formulations for the average magnetic field at a domain wall are presented. The problem of cutting bubbles off from a strip wall is investigated. It is seen that the field required to cut off a bubble can be up to 40 percent less than the 4πMsrequired to push two parallel walls together for certain geometries View full abstract»

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  • Three-dimensional nonlinear magnetic field boundary value problem and its numerical solution

    Publication Year: 1970 , Page(s): 828 - 833
    Cited by:  Papers (5)
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    An accurate solution to the nonlinear magnetic field boundary value problem which results when ferromagnetic materials are present is generally very difficult to obtain. Several computer codes based on a magnetic vector potential have been published in the literature. While those codes can be used to solve 2-dimensional problems, difficulties arise in their application to 3-dimensional problems. One difficulty is the complexity of the resulting differential equations which must be solved. This paper treats the more complex 3-dimensional solutions as derived from the concept of a scalar magnetic potential. The most desirable feature of this approach is that the magnetic material characteristics are incorporated directly into one second order nonlinear partial differential equation which can be solved on a digital computer using standard finite difference schemes. In order to add credence to the validity of the technique presented, a simple 3-dimensional magnetic field boundary value problem is posed and solved. View full abstract»

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  • AC losses of high-field superconductors

    Publication Year: 1970 , Page(s): 833 - 839
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    The Riemersma critical state model is applied to a long irreversible type-II superconductor carrying ac. Voltage waveforms, energy loss per cycle, and limiting values of effective resistivity are derived. For sinusoidal current of frequency f in 10-mil wire the critical current limit of resistivity is 4.06 × 10-14f (ω.m). An equivalent circuit consisting of a variable inductance is proposed. Ex-perinlents at 4.2°K on bifilar windings of bare and copper-plated single-strand 10-mil nb-25Zr wire at 60, 400, and 800 Hz gave only fair agreement with the model with indications that the model can be improved by including surface hysteresis and eddy-current effects. Experimental values of resistivity agree more with Zar than with Wisseman, leading to the conclusion that continuous ac power applications of superconductivity are not attractive for the sake of efficiency. There remains some promise for dc energy storage for discharge into pulse power devices. View full abstract»

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  • Effect of leakage and source inductances on the switching pattern of a magnetically coupled tunnel diode oscillator

    Publication Year: 1970 , Page(s): 840 - 844
    Cited by:  Papers (1)
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    A magnetically coupled tunnel diode oscillator employing a square-loop core is analyzed. Particular emphasis is given to understanding the effects of small, yet inevitable, leakage inductances and the inductance of the dc source on the switching pattern of the tunnel diodes. The combined size of these inductances is found to be the determining factor that leads to many unusual switching phenomena encountered with the inverter. Included in these phenomena is the delayed switching of the tunnel diodes, which manifests itself in the formation of a quasi-square wave at the inverter output in what can be a serious loss in efficiency. Physical explanations and mathematical analysis which bring into focus the significant effects of these stray elements are presented. View full abstract»

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  • Functional stability conditions for logic devices of K- valued logic

    Publication Year: 1970 , Page(s): 844 - 846
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    For any input signal of logic elements (LE) which realize logical functions of K -valued logic to be converted into any output signal, it has been shown to be sufficient that the LE have 2(K- 1) different input-output characteristics without equal values of the output signal at neighboring discrete values of input signals. Sufficient conditions for stable operation of both long closed and short logical chains of elements with characteristics under consideration are formulated. View full abstract»

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  • A statistical model of core noise in half-wave push-pull magnetic amplifiers

    Publication Year: 1970 , Page(s): 847 - 849
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    The core noise was measured for the half-wave push-pull magnetic amplifiers using various ferromagnetic materials as functions of the number of laminations of a stacked ring core and ac supply frequency. A statistical model of the core noise is proposed. It was deduced that the mean number of magnetic elementary regions associated with the core noise is proportional to values ranging from f to f^{3/5} , where f is the ac frequency. View full abstract»

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  • On the nature of mirror substrates

    Publication Year: 1970 , Page(s): 849 - 850
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    The use of reflecting substrates to enhance the Kerr magnetooptic effect has frequently been discussed. The nature of such a realizable high reflectivity mirror is described in a simple way. View full abstract»

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  • Influence of cobalt on annealing of zero magnetostrictive Ni-Fe-Co films

    Publication Year: 1970 , Page(s): 851 - 853
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    Zero magnetostrictive films about 1000 Å thick with cobalt contents from 0 to approximately 50 percent have been subjected to easy- and hard-axis saturating fields. The changes in characteristics were examined on aging for four hours in 30°C steps up to 240°C. Anisotropy field, dispersion, and coercive force were examined. The anisotropy and dispersion changes on aging indicated somewhat faster aging for samples with increasing cobalt. This is as expected for an M -induced annealing mechanism. However, the differences were small; maximum differences in the parameters, after aging to 150°C, between samples with different cobalt contents were ±10 percent. View full abstract»

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  • Light modified switching properties of garnets and ferrites

    Publication Year: 1970 , Page(s): 853 - 857
    Cited by:  Papers (1)
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    The influence of light on the switching behavior of Si-doped Y3Fe5O12and Co-substituted Ni-Zn ferrites is investigated. After irradiation with light, YIG (Si) has an extremely square hysteresis loop, and the switching transients display anomalous behavior. When a step field is applied, there is a certain period of time during which no flux is switched irreversibly. After this delay, which depends on the amplitude of the applied step field, the material switches in the normal way. At 4.2 and 77°K these changes are permanent; at 200°K the effects disappear after illumination is terminated. The results are discussed in terms of a two-center model, which was proposed earlier to explain results for changes in permeability. Co-substituted Ni-Zn ferrites show similar behavior already in the nonirradiated state. Irradiation increases the coercive force and also the break-free behavior becomes more pronounced. These changes are still permanent at 200°K. View full abstract»

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  • Surface spin pinnning model for magnetic properties of oxidized thin films on substrates

    Publication Year: 1970 , Page(s): 857 - 862
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    A simple model for oxidized thin ferromagnetic film deposited on a substrate based on the concept of surface spin pinning is proposed. A spin wave analysis of the spatial distribution of the magnetization through the film thickness, as well as of the total relative magnetization, is performed. Qualitative results are reported for three different cases: complete pinning of spins on both surfaces, one pinned and one free surface, and two free surfaces. It is shown that an appropriate choice of the surface anisotropy could account for various positions of standing spin wave resonances, even contradictory ones, as reported in the literature. 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