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Magnetics, IEEE Transactions on

Issue 3 • Date September 1965

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Displaying Results 1 - 14 of 14
  • [Front cover and table of contents]

    Page(s): 0
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  • Potential applications of magnetic rare earth compunds

    Page(s): 144 - 155
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    Chemistry and physics of the rare earth elements and their compounds are in a rapidly expanding state of development. Many new materials with interesting magnetic properties have recently become available. The potential of lanthanon compounds as magnetic materials in electrical engineering is evaluated by comparing the basic properties of lanthanons and transition metals. The lanthanides show certain unique properties resulting from the localization of their magnetic4flevels. Unfortunately, their Curie temperatures are relatively low. The probability of finding ferromagnetic lanthanide compounds with high Curie temperatures is explored. A survey of magnetic properties of metallic and nonmetallic lanthanide materials indicates possible applications for which they can compete favorably with other materials. View full abstract»

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  • Magnetic measurements with Lorentz microscopy

    Page(s): 156 - 167
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    The electron microscope may be operated in a mode which permits the exploration of the magnetization configurations in thin magnetic films. This mode of operation, known as Lorentz microscopy, is a powerful technique for investigating thin NiFe films because it offers high resolution, because it provides an unequivocal identification of the local magnetization direction, and because it permits correlations to be made between the magnetic structure and the underlying physical (crystallographic) structure of the film. In the past, Lorentz microscopy has found fruitful employment in the analysis of the magnetization configurations of domain walls, in studies of various magnetization reversal processes, and in specialized investigations of unusual magnetic structure. Besides these primarily qualitative investigations, however, some quantitative measurements may be made with this instrument. Such measurements are useful not only because they permit direct evaluation of basic magnetic parameters of films being studied by Lorentz microscopy, but because they afford insight into the fundamental processes which occur in the standard macroscopic magnetic measurements of NiFe films deposited on glass substrates. The following measurements are discussed: 1) determination of the Curie temperature; 2) measurement of the anisotropy field Hkby the standard hysteresigraph and the Feldtkeller techniques; 3) quantitative studies of wall motion by labyrinth propagation and by wall creep; 4) the investigation of anisotropy dispersion by the Crowther and Torok techniques. The accuracy of these measurements is, in general, lower than that of the analogous measurements made by macroscopic methods on films deposited on glass substrates. Nevertheless, macroscopic measurements performed on a film on a glass substrate showed good agreement with Lorentz measurements performed on a simultaneously-deposited film which was suitable for Lorentz microscopy. View full abstract»

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  • Ultimate performance limitations of high-power ferrite circulators and phase shifters

    Page(s): 168 - 174
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    The power-handling capability of circulators and phase shifters in rectangular waveguide is analyzed. It is shown that an appropriate measure of the suitability of microwave ferrites for high-power applications is given by the "high-power figure of merit"F_{hp}* = 4piMgamma^{2}h_{crit}/omega^{2}mu''. Here γ is the gyromagnetic ratio, hcritthe critical RF field, ω the (angular) frequency,mu"the imaginary part of the diagonal component of the permeability tensor. In applications to nonlatching devices,Mis the saturation magnetization; in applications to latching devices it is the remanent magnetization. The figures of merit of various rare-earth substituted garnets are reported. The figures of merit obtained to date are approximately 2. Theoretical analysis indicates that significantly larger figures of merit can be Obtained only at the cost of reducing the saturation magnetization. It is concluded that for circulators using theH-plane configuration and having an insertion loss of 0.5 dB the maximum attainable peak power level is of the order of 50 MW. For latching twin slab phase shifters (E-plane configuration) having an insertion loss of 1 dB the maximum attainable peak power level is estimated to be 80 kW. View full abstract»

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  • Indirectly coupled films

    Page(s): 174 - 180
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    A positive coupling has been observed between magnetic films separated by a thin metallic layer. Five methods which have been developed for measuring this coupling and the variation of the coupling with evaporation temperature, measuring temperature, and thickness of the intermediate layer are described. Three mechanisms are proposed for the observed coupling : bulk diffusion of ferromagnetic atoms into the intermediate layer, diffusion of magnetic atoms along grain boundaries, and polarization of conduction electrons. The effect of this coupling on slow switching, pulse switching, and creep is discussed. View full abstract»

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  • Comparison of magnetic behavior of cylindrical and flat films from Kerr effect probe measurements

    Page(s): 180 - 185
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    The magnetic characteristics of flat and cylindrical permalloy films are compared. 1000 Å-flat films and 10 000-Å cylindrical films electrodeposited onto 5-mil-diameter wires show very similar magnetic properties. Geometrical differences arise largely in the relative ease or difficulty with which fields may be applied to the films and signals extracted. The greater thickness of the cylindrical films described gives rise to enhanced magnetostatic effects apparent in the Kerr effect probe measurements and to strong self-shielding against nonaxial external fields. View full abstract»

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  • Engineering aspects of magnetic film memories

    Page(s): 185 - 192
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    Some of the more pertinent engineering aspects relating to the design of magnetic film destructive readout (DRO) memories are given, together with a brief reference to nondestructive readout memories. The technical discussion centers primarily on three major areas: 1) storage element characteristics such as skew, dispersion, disturb threshold, and magnetostriction, and how these relate to element fabrication and memory design; 2) memory plane design, with reference to primary effects of eddy currents, fringing fields, and sense line arrangements; 3) special circuit considerations as they relate to film memories. Much of the information presented is general enough to apply to various design approaches. However, specific examples and results obtained with production models of the FFM-202 memory system are used for purposes of illustration. A number of these 300-ns memories are now operating in the field, and current margins obtainable have been superior to those of coincident current core memories. DRO magnetic film memories are presently used in data processing equipment mainly as scratchpads, either as internal stores or as high-speed input/output buffers. However, the real impact of thin film units will be felt when they are commercially available as relatively large building-block modules in the range of 4096 words of 74 bits, at speeds of 200 to 400 ns and at costs competitive with one μs coincident current core memories. The present low costs of semiconductors have alleviated most of the disadvantages of word organization, particularly in magnetic films where only a relatively low-power, unipolar word pulse is needed. Also, the associated low drive power reduces heat dissipation and makes simpler a more compact modular design. This is needed to reduce logic delays in large capacity, high-speed systems. In order to obtain a large capacity, low-cost film memory, primary engineering problems involving the memory stack must be solved. As an example of one desirable approach, a plane design with increased bit density (which results in reduced costs per bit and shorter delays) is described, together with some preliminary results obtained. View full abstract»

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  • Thin metallic films for high-density digital recording

    Page(s): 193 - 205
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    Three different methods, electrodeposition, autocatalytic deposition, and vacuum deposition, by which thin metal films may be made are described. They have a combination of magnetic characteristics which should make them well suited to the purpose of high density recording. It is concluded that the factors which are primarily responsible for the superior recording performance of these films when compared with the conventional particulate coatings are their thinness and their high coercivity. View full abstract»

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  • Storage systems--Present status and anticipated development

    Page(s): 206 - 211
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    The state of the art of computer memories is discussed with respect to the increasing variety of memory systems and functions. Present speed and capacity limits will be given. New technologies and concepts will be reviewed and fundamental barriers are identified. Their review leads to an estimate of the progress to be expected in the next few years. View full abstract»

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  • Basic deposited integrated magnetic circuit element for fast computer circuitry

    Page(s): 211 - 217
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    A deposited configuration, consisting of a magnetic thin film and coupling loop, was studied with a view to the future development of integrated magnetic circuitry. A line charge model, predicting flux linkages of coupling loops to an accuracy of about one percent was established. The almost complete linkage of the film flux with a deposited loop, due to the very close coupling, was verified. A decrease of about 20 percent in film flux at both ends of the easy axis was noted for the experimental assemblies used. Circulating loop currents were shown to be the chief parasitic factor which modified the switching of the magnetic film. The change in switching time due to eddy currents was small when the loop conductor size was of the same order as the magnetic film. For resistive loop loading, the average field during switching is a good measure of the slowing due to the loading. The film-loop assembly has good potentialities as a circuit element, with good transmission of both read-out and control signals occurring in the loop. The field calibration for these control signals was shown to be the same for both bias and drive field applications. View full abstract»

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  • Computation of flux switching in magnetic circuits

    Page(s): 222 - 234
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    A number of physical and semiempirical flux-switching models that have appeared in the literature are reviewed briefly and classified. A thin ferrite core is switched by essentially a step mmf (with short rise time Tr). Three components of the totaldot{phi}(t)are distinguished and semiempirical models are proposed for each : 1) an initial elasticdot{phi}spike during the rise time ofF, dot{phi}_{epsilon} = epsilondot{F}, where ε is constant in time; 2) a decaying inelasticdot{phi}starting att cong T_{r},dot{phi}_{rho i} = rho_{i}(F - F_{d}^{min}) exp [-(t - T_{r})(F - F_{d}^{min})/C_{i}], where ρiand Ciare constants in time andF_{d}^{min}is the static mmf threshold; and 3) the bell-shaped, main inelasticdot{phi}, dot{phi} = dot{phi}_{p}{1 - [(2phi + phi_{s} - phi_{d})/(phi_{s} + phi_{d})]^{2}}, where, for givenF , phi_{p}is the peak ofdot{phi}, phi_{d}is the φ value on the staticphi(F)curve, and φsis saturation flux. Expressions involving switching parameters are given forepsilon, dot{phi}_{p}, and φd. The agreement between these models andphi(t)of a thin core is satisfactory. The main-dot{phi}model is applied in a numerical analysis of three magnetic circuits: an unloaded core, a core loaded byR, L, C, and a diode, and a core-diode shift register. The agreement between computed and experimental results is satisfactory, especially if different parameters are used for computing step-Fand ramp-Fswitching. View full abstract»

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  • [Back cover]

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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