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Magnetics, IEEE Transactions on

Issue 2 • Date June 1967

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

    Page(s): 0
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  • Magnetic scan head for high-frequency recording

    Page(s): 96 - 100
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    A stationary magnetic head scans the width of a record magnetically, enabling successive lines of video information to be recorded on a slowly moving tape. The head contains a large number of laminations. All except one of these are blocked from transducing action with the tape by currents through sweep windings. As the sweep currents are changed, every lamination becomes active in succession. For playback, such a head operates on a magnetic-modulator principle which is sensitive to flux rather than to its rate-of-change. View full abstract»

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  • On the dynamic properties of cascaded self-saturating magnetic amplifiers

    Page(s): 100 - 107
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    The influence of some parameters of the 2-stage self-saturating magnetic amplifier on its steady-state and transient properties is described. It is shown that applying anR,Cfilter between both stages ensures proper operation of the amplifier. On the basis of the difference equations describing the single stage self-saturating magnetic amplifier, the discrete transmittance of the circuit can be derived. It is pointed out that the back reaction of the second stage on the first appears in cascade. The time constants of the cascade are not equal to the time constants of stages working separately. The influence of the electric and magnetic feedback loop over both stages on the stability of the circuit is considered. There are given conditions under which, when the transient state is caused by a jump change of control voltage, the cascade output voltage appears as an exponential function with two time constants, damped oscillations, or self-sustained oscillations. Characteristic parameters of the cascaded magnetic amplifier are determined. Theoretical results were compared with laboratory investigations. View full abstract»

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  • Stability analyses of self-saturating magnetic amplifiers with capactive load

    Page(s): 108 - 116
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    Analyses of the self-saturating magnetic amplifiers are generally restricted to the pure resistive load cases. There are a few reports related to capacitive loads and some others on inductive loads. The possibility of occurrence of abnormal phenomena in the self-saturating magnetic amplifier with capacitive load has been reported, but their mechanism of circuit behavior is not yet clear. In this paper, the circuit operation is analyzed in detail from the stability point of view and the mechanism of peculiar modes is investigated. The circuit operation is represented by the nonlinear difference equations which are derived from the continuity of both charge and flux linkage. Linear difference equations for small disturbances occurring at the equilibrium state directly suggest the stability of the equilibrium state and possibility of occurrences of the peculiar modes. Further, the control characteristics and the transient responses are calculated and the criteria for prevention of the peculiar modes are found in simple forms. The theoretical analyses show good agreement with experimental results. View full abstract»

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  • Polyphase multivibrators

    Page(s): 117 - 124
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    A new type of polyphase multivibrator is introduced in which saturable cores are the timing elements and transistors the switching elements. The basic units are like the multivibrators invented by Royer and others, but, in the new polyphase circuit, several single-phase multivibrators with a common dc source are constrained by a loop connection of windings on the cores in such a way that polyphase output voltages are obtained. Detailed analysis of a typical 3-phase circuit leads to conclusions regarding the frequency of oscillation and the output voltage waveforms which conform to experimental observations. Novel arrangements are presented by means of which 2-phase voltages can be obtained from a 3-phase multivibrator. View full abstract»

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  • Analysis of minor loop behavior during alternating flux reversal in rectangular-loop toroidal cores

    Page(s): 125 - 135
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    The analysis of minor hysteresis loop behavior during partial alternating flux reversal in toroidal cores with a rectangular hysteresis loop is considered. A simple flux-reversal model is proposed on the basis of which, with the aid of dimensionless units, the asymmetry of minor hysteresis loops is derived. The drift of minor hysteresis loops during alternating flux reversal is investigated on the basis of loop asymmetry and by means of a proposed indirect method. The method involves compensation of the minor-loop drift by means of a dc component of the exciting field, the magnitude and sense of which are a measure of the drift. The experimental section deals partly with a qualitative comparison of the character of the actual asymmetry of a minor loop with that derived from the flux reversal model, and partly with comparing the actual minor-loop drift to the drift derived theoretically on the basis of the indirect method. Experimental results indicate that in the case of the 50 percent nickel-iron alloy, cold-rolled at a great reduction, there appear additional factors which affect the instability of the minor loop. This effect is further investigated, and a simplified mechanism is proposed for its stimulation. Finally, the proposed mechanism is verified experimentally. View full abstract»

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  • Design of half-million bit wire memory

    Page(s): 135 - 141
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    A high volumetric density wire memory stack of 12 000 bits/in3was designed. The high bit density was obtained by the introduction of a novel and continuous digit line printed circuit which is also used to separate and support the plated wires. The printed circuit is also used for interconnecting the planes of the memory stack. Analysis of digit current and signal coupling is given. The advantages of the proposed memory stack configuration are apparent. These include low digit current and digit signal coupling along with good word and digit noise cancellations and high bit density. View full abstract»

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  • Magnetization creep in magnetic films

    Page(s): 141 - 157
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    Magnetization reversal in planar magnetic films can occur for field amplitudes well below the static threshold. Repeated field transitions parallel to a film's hard axis in the presence of an easy-axis field can cause slow motion or creeping of the domain boundaries. Experimental observations of magnetization creep and proposed creep mechanisms are reviewed. Creep was studied in slow-rising sinewave and pulsed hard-axis fields. The effective creep thresholds obtained for these cases are compared. In an operating mode in which a bipolar easy-axis pulse and a unipolar word pulse are used, creep is reduced and the effective creep threshold is improved. Examples of domain growth in unipolar and bipolar hard-axis fields are shown in a series of Kerr optical photographs demonstrating the creep process. View full abstract»

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  • Mathematical models for loss measurements in thin permalloy films with ramp drives

    Page(s): 162 - 165
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    Uniaxial thin Permalloy films are driven with a large amplitude sinusoidalHfield in order to approximate a ramp drive. TheHfield is characterized by rise times which exceed3 times 10^{6}Oe/s. Two mathematical models are suggested to represent the loss measurements obtained in a domain wall motion region and in an incoherent rotation region. A normalized loss threshold is determined which characterizes the transition between the two regions. In the slow reversal or wall motion region, the normalized losses are proportional to the square root of α whereH = alpha t. In the relatively fast reversal or incoherent rotation region, the normalized losses are proportional to α. In both cases the inverse switching time is proportional to the coercive force in excess of the static value. Experimental data verify the reasonableness of the mathematical models. View full abstract»

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  • The effects of metallic underlayers on Properties of permalloy films

    Page(s): 157 - 162
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    Thin Permalloy films of zero-magnetostrictive composition were evaporated on a variety of metal film underlayers of various thicknesses (which were deposited on glass substrates) and also on smooth metallic substrates. In contrast to Prosen et al., however, the observed uniaxial magnetic anisotropy is not zero. In thin Permalloy films (100-1000 Å) deposited on high melting-point metal films (Mo, Ti, Pd, and Cr), essentially the same anisotropy field is obtained as is normally observed on glass substrates. In these films the coercivity and the angular dispersion increase slightly as the underlayer thickness increases. Permalloy properties on low melting-point metals (Au, Ag, Cu, and Al) depend strongly upon the underlayer thickness. At a given substrate temperature, a maximum in coercivity and angular dispersion is found in ∼100 Å thick underlayers of Au, Ag, and Cu. In Al underlayers, the values of coercive force along the easy and hard axis increase rapidly as a function of thickness. Large values of the easy-axis skew are obtained in all metal underlayers where the direction of the skew depends upon the geometrical arrangement of the vapor source (Permalloy) and the substrate. These effects are attributed to the microstructure and morphology of the underlayers. Electron microscopy studies are presented in confirmation of these surface geometrical effects. View full abstract»

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  • A study of noncoherent rotational switching for thin magnetic films

    Page(s): 166 - 170
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    Thin magnetic film switching was investigated for fields near those needed for pure rotation. Experimentally the films were switched using <0.4 ns rise time field pulses. The resulting flux changes were detected in the easy and hard direction with a response time of 0.6 ns. Measurements were made for pulses both longer and shorter than the magnetization switching times. By analyzing the voltage waveforms and flux changes, it was concluded that instabilities and rapid rearrangements of the magnetization can occur within a few nanoseconds, causing anomalous results during switching. Equations of existing quantitative switching models-pure rotation, spin-wave, and stripe domain-were solved with a digital computer. To better compare theory and experiment, the solutions were modified to account for the sense system's finite rise time. It was found that none of the existing models adequately described the switching processes for low amplitude magnetic fields. However, qualitatively, the stripe domain model best fit the experimental data. View full abstract»

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  • Contributors and 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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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology