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Magnetics, IEEE Transactions on

Issue 4 • Date December 1972

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Displaying Results 1 - 16 of 16
  • [Front cover and table of contents]

    Page(s): 0
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  • A transient solution for domain wall motion

    Page(s): 741 - 743
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    Approximate analytic solutions of transient wall motion in a bulk ferromagnetic material are obtained from the dynamic torque equations with a Gilbert damping term. These transient solutions reduce to previously obtained well-known solutions under steady-state velocity conditions. View full abstract»

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  • Wall contraction in Bloch wall films

    Page(s): 743 - 746
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    The phenomenon of wall contraction characterized by a peak in the velocity-field relationship and a region of negative differential mobility is observed in uniaxial magnetic thin films of various magnetic properties by careful interrupted-pulse experiments. The observed results agree quite well with the theory for bulk samples when the extensive flux closure of thin film walls is accounted for by a suitable empirical scaling factor. View full abstract»

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  • Cylindrical-domain propagation by Permalloy bar stray fields

    Page(s): 746 - 753
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    The field gradients of magnetic stray fields which affect the propagation of cylindrical domains in a T-bar pattern are investigated. The magnetization of the Permalloy bars which gives rise to the propagating field gradient is found to be influenced by the stray field of the cylindrical domain itself. Considering this interaction, the propagating field gradients are calculated first for single bars and then for a geometric arrangement as it occurs in a T-bar pattern. Those forces leading to a forward propagation and those leading to a trapping of the domain are studied. Useful relations for the distance between the adjacent bars are deduced. The calculated propagating field gradient is found to have considerable local variations. This causes corresponding velocity variations of the domain. The marked velocity minima which occur along the domain path represent a strong restriction to high data rates in domain memory devices. Average propagation fields for the different propagation steps are shown as a function of the bar width. View full abstract»

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  • The effects of spacing between garnet film and Permalloy overlay circuit in magnetic bubble devices

    Page(s): 754 - 758
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    An experimental test set for magnetic bubble devices has been constructed in which the spacing between the garnet film and the Permalloy overlay is variable. The experimental uncertainty in spacing is approximatelypm.15mum, and spacings as small as.5mum have been attained. Bias margin data are presented which were taken at 1 Hz on a 20 micron period chevron circuit as a function of spacing. The collapse and strip-out fields begin to be affected when the spacing is comparable to the garnet film thickness, increasing as the spacing decreases. At larger spacing the high-bias failure mode changes from collapse to uncorrelated bubble motion. A theoretical model which accounts for some aspects of the spacing dependence of the strip-out and collapse fields is described. This model approximates the circuit by a continuous Permalloy sheet. At the low spacing required for efficient use of the rotating field, the model indicates that ±10% nonuniformity in a 2 micron spacing over the device area results in a degradation of the bias field operating range by about 12%. View full abstract»

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  • Magnetic materials for integrated cores

    Page(s): 759 - 764
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    Magnetic materials for an integrated magnetic core memory have been developed. The materials are for a storage layer about 1 μm thick and a low reluctance keeper layer. Materials investigated were Co-Ni-Fe for the storage layer and Cr-Ni-Fe for the keeper. Measurements were made ofH_{c}, B_{s}, B_{r}, lambda_{s}, S_{w}, H_{0}, and Hdisturb. Layer stress and adhesion were also measured. Special apparatus, which is described, has been developed to perform some of the measurements. Variation of properties with substrate surface, substrate temperature, and oxygen pressure during evaporation are reported. View full abstract»

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  • Memory-core characteristics of cobalt substituted lithium ferrite

    Page(s): 765 - 769
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    The memory-core characteristics of compositions in the system Li0.47-1/2x-1/2yCoxZnyNi0.06Fe2.47-1/2x-1/2yO4have been studied. The cobalt and zinc contents have been varied from zero to 0.02 and from zero to 0.12, respectively. It is demonstrated that small amounts of cobalt decrease the temperature coefficient of the coercive force and, in the zinc-containing materials, produce improved square-loop properties. These materials demonstrate improved pulse response properties when compared with unsubstituted lithium ferrite. View full abstract»

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  • Influence of extreme dilutions on the magnetic properties of single-domain particle aggregates

    Page(s): 770 - 772
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    Various magnetic properties of samples of single-domain particles dispersed in a nonmagnetic matrix are examined as functions of the packing fractionp. The range of variability ofpis from 0.0003 to 0.20. The squareness ratio and the rotational and alternating hysteresis integrals change withp, while the coercive field, the initial anhysteretic susceptibility, and the areas between the remanence curves are not dependent onp. These results are interpretated as a consequence of the formation of agglomerates interacting with each other, rather than as a consequence of analogous interactions among the single-domain particles which are in the aggregate. View full abstract»

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  • Investigation of the inverted state of nuclear magnetic levels in Co59films

    Page(s): 773 - 774
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    Experiments that yield inversion of the Co59thin film nuclear system were carried out. For nanosecond magnetization reversal by a field with a growth rate greater than5 cdot 10^{11}Oe/s, 85% inversion was obtained. The investigation of the inverted state at frequencies corresponding to hexagonal (α) and f.c.c. (β) phases revealed that Co59-β switches 1.3 times faster than Co59-α. This is explained by the large contribution of rotational processes for Co59in β phase. Longitudinal relaxation time T1is measured by the method of pulse inversion. View full abstract»

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  • Transient eddy currents in thin metal sheets

    Page(s): 775 - 779
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    In the present paper, an approach is outlined to the solution of the transient eddy currents produced upon field switching in a thin nonmagnetic metal layer. The results may be used in evaluating the distribution of the transient volume force densities acting on the metal. Some of the fields in which problems of this kind arise are power equipment shielding, nondestructive eddy current test instrumentation, and magnetic levitation. View full abstract»

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  • The magnetic mixing amplifier

    Page(s): 780 - 785
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    A new type of magnetic signal mixing amplifier is introduced which is useful for the treatment of multisignals biased with different levels of potential. A saturable core and transistors are its basic components. This mixing amplifier is excellent in linearity, has push-pull with an inherently single core, has a quick response, and is operated with a dc source. Decoupling of the input and output is made possible by use of the three-core configuration. An arrangement is also presented in which the isolation of the output from the dc source can be attained by the use of other windings. View full abstract»

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  • Power loss and flux density distributions in the T-joint of a three phase transformer core

    Page(s): 785 - 790
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    A three phase transformer test facility has been used for measuring the localized power loss and flux distribution within the core. The flux and loss distributions in the T-joint of a core with simple double overlap joints have been investigated. The flux density distribution was measured by an array of search coils wound on individual laminations, and the localized power loss was found by measuring the initial rate of temperature rise using miniature thermocouples. For measurements made in the range of flux densities from 1.1 to 1.6 T, the inner edges of the yoke and limb laminations were the highest loss areas, up to 30% higher than the mean core loss. These regions of high power loss were found to be due to a high third harmonic flux density component being present. The fundamental component of flux density tended to follow the rolling direction of both yoke and limb laminations; however, some deviation from the rolling direction was present in the case of other harmonics. View full abstract»

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  • The theoretical output of a ring core fluxgate sensor

    Page(s): 791 - 796
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    This article proves that the output from a ring core sensor is directly proportional to the first time derivative of the product of dynamic permeability and magnetic intensity perturbation within the core caused by an external, uniform magnetic field. (Dynamic permeability is defined to be the slope of the hysteresis loop at a given point in time.) Assuming that ellipsoidal shells can approximate the core, the demagnetization factor can be "estimated" in the first order to be proportional to the first power of the quantity tape thickness (or number of wraps) divided by the core diameter. The constant of proportionality is determined from laboratory data. When an additional scale adjustment is applied to the resulting sensor output formula, the computed output tracks laboratory data for a range of sensor geometries. View full abstract»

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  • [Back cover]

    Page(s): 0
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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