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Magnetics, IEEE Transactions on

Issue 3 • Date September 1967

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Displaying Results 1 - 25 of 110
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • 1967 INTERMAG Conference welcoming remarks

    Page(s): 189
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    Freely Available from IEEE
  • Chemical vapor deposition of epitaxial garnet films

    Page(s): 190 - 194
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    The chemical vapor deposition of single crystal metal oxides has recently been extended to the growth of certain epitaxial garnets, in particular YIG on YAG and GdIG on YAG. The light green, transparent films aresim3muthick and are limited in area only by the area of the available YAG seeds. On View full abstract»

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  • Magnetic recording theories: Accomplishments and unresolved problems

    Page(s): 195 - 200
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    The published theoretical treatments on the magnetic recording process are reviewed with particular emphasis on the validity of the models and the assumptions on which they are based. It is concluded that the existing theories fairly well describe the geometrical aspects of recording-transducer to medium spacing and gap lengths-but are deficient in describing analytically the magnetic state of the recording medium before and after demagnetization. Calculated magnetization distributions by harmonic analysis for different recording media are in support of the fact that the usually assumed linear and arctangent magnetization transitions are only rough approximations of the magnetic state of a recording medium between regions of opposite magnetization. Additional shortcomings of our theoretical understanding are indicated by the assumptions of uniform magnetization through the recording medium thickness, neglecting the perpendicular component of the magnetization, and not taking into account finite track widths and magnetostatic interactions between adjacent transitions. View full abstract»

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  • Novel technique for the measurement of demagnetizing fields in longitudinal recording

    Page(s): 201 - 204
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    The maximum losses occurring at very short wavelengths, due to demagnetization in γFe2O3tape, have been calculated to be rather small (4.5 dB and 8 dB for magnetic and non-magnetic head reproduction, respectively) and they are therefore difficult to measure in the face of the relatively large and indeterminate spacing loss. A method is described for testing a particular tape in free space which avoids the difficulty. Essentially, a determination of the incremental remanent susceptibility of the tape is made. Because the remanence curve is so highly nonlinear, this susceptibility is uniquely associated with the demagnetizing field within the tape. Whereas the demagnetizing fields thus found agree with theory for wavelengths greater than 1 mil, they decrease, contrary to expectations, at the shorter wavelengths. View full abstract»

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  • Thin evaporated films with high coercive force

    Page(s): 205 - 207
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    A technique allowing the preparation by vacuum evaporation of a material useable as a storage medium in digital magnetic recording is described. It consists of the evaporation of successive chromium and cobalt layers on a substrate, the nature of which seems indifferent. The coercive force can be adjusted from 200 to 600 Oe by adjusting the cobalt layer thickness. Superimposing identical double layers of chromium-cobalt allows one to obtain the required amount of flux. Such a multiple layered film gives properties identical to those of a homogeneous magnetic material with a coercive force between 200-600 Oe and an induction better than 10 000 gauss. These properties are isotropic. High squareness of the hysteresis cycle, with Mr/Ms > 0.95, is achieved. View full abstract»

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  • Study of peak shift in thin recording surfaces

    Page(s): 208 - 211
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    One of the most severe limitations on high-density digital recording is imposed by peak shift, which is defined as the outward displacement of the readback signal peaks corresponding to a recorded bit pattern of two successive ones followed and preceded by a number of zeros. Results of an experimental study of peak shift in thin metallic media are represented along with a correlation of the measured percent peak shift with the magnetic properties and the thickness of the media. It was found that the percent peak shift at a specified bit density varies proportionally with the thickness of the coercivity ratio for coercivities larger than 250 Oe. For lower coercivities, the remanent magnetization of the recording surface becomes increasingly significant in adversely affecting the peak shift, with a corresponding decrease in the importance of thickness. By superposing isolated pulses it was possible to predict the percent peak shift up to extremely large bit densities. View full abstract»

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  • Factors influencing write current in NRZ recording

    Page(s): 212 - 216
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    The concept is advanced that the write head current amplitude which produces maximum output for a given set of recording conditions can be determined by three nearly independent factors. The first is a static factor related to the head geometry and reluctance at very low frequencies. The second is a time factor related to the tape speed and transient response of the head and the third, a density factor, is determined by the recorded bit density. The time and density factors can be expressed by a set of normalized curves which are relatively independent of head characteristics. View full abstract»

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  • Effects of the writing process and crosstalk on the timing accuracy of pulses in NRZ digital recording

    Page(s): 217 - 222
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    The position at which a NRZ transition is recorded is dependent on the write current, the effect of increasing the current being to shift the recorded position beyond the trailing gap edge. The shift is more marked with a thick medium than a thin coating, and is worsened if the write head pole tips are approaching saturation. If the recording field changes magnitude when reversed, positive pulses become displaced relative to negative, and pulse pairing occurs. When recording different patterns on adjacent tracks, peak shifts can occur due to writing crosstalk aiding or opposing the head field and the shifts may well impose an upper limit to track density. View full abstract»

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  • Thyristor converters using saturable reactors

    Page(s): 224 - 228
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    The dc to ac and ac to ac series converters have been discussed in earlier publications.[1]-[3] These systems are used with minimum component ratings at a fixed load resistance and a fixed output frequency.[1] The ranges of operation of the load and the frequency can be increased by using saturable reactors and variable capacitors. These systems are analyzed and the preferred operating conditions are discussed. Theoretical results are supplemented with the experimental results. View full abstract»

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  • Nonlinear reactors as protective elements for thyristor circuits

    Page(s): 228 - 232
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    Control of rate of change of current and voltage in thyristor power circuits is provided in diverse ways according to the special features of the particular problem and the ingenuity of the designer. It is shown that the use of a nonlinear reactor in series with the thyristor provides advantages in some surge suppression networks, and a design technique is presented for these reactors. Characteristics of a basic damping circuit are presented in the form of non-dimensional design curves, and a relationship is established between the losses of a surge suppression network and the thyristorpartiali/partialtandpartialV/partialtcapabilities. View full abstract»

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  • High-voltage multiple phase thyristor chopper for traction motor control

    Page(s): 232 - 236
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    The dc chopper drive of traction motors using thyristors has many advantages such as the improvement of efficiency, stepless control of motor current, and the elimination of mechanical contactors and the associated maintenance. A considerable amount of literature has been published concerning chopper circuitry and its application to dc motor control. There are some problems to be solved, however, for the actual application in electric railways ; the first is the realization of a high-voltage chopper, the second is the reduction of inductive interference, and the third is the reduction of weight and cost of chopper equipment. The characteristics of a multiple phase chopper circuit which has been developed for traction motor control systems are described. The multiple phase chopper with common load has proved to have the excellent property of reducing the higher harmonic components both in input current and in output current. This results in reducing the inductive interference and minimizing the weight of the smoothing reactor. View full abstract»

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  • The thyristor commutatorless motor

    Page(s): 236 - 240
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    The commutatorless motor (CLM) is a type of a dc motor whose commutator is replaced by the thyristor power converter. The thyristors are switched by the signals from a position sensor connected to the rotating shaft of the synchronous motor. Therefore, the CLM never loses synchronism and has the good speed characteristics of a dc motor. The current type CLM, having a current smoothing reactor, was studied and found to have better characteristics than the voltage type. In this paper two kinds of the current type CLMs are described; one is the dc CLM using an inverter, the other the ac CLM using a cycloconverter. View full abstract»

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  • Thyristor-controlled single phase variable inductor

    Page(s): 240 - 245
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    This paper describes a system which provides a smoothly variable inductor using thyristors to switch the input current and a unique technique to reduce undesirable harmonics. The basic principle is outlined, and the theory of harmonic reduction is developed. Operation of the circuit is described and mathematical analysis is obtained for the system. The circuit parameters are optimized for minimum harmonic contents in the input current over a wide range. View full abstract»

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  • Frequency control technique applicable to either voltage- or current-feedback magnetically-coupled switching-transistor oscillators

    Page(s): 245 - 250
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    Through the use of nonlinear circuit techniques similar to those normally associated with series-connected magnetic amplifiers, it is possible to modify the basic circuits of almost all of the numerous types of magnetically-coupled switching-transistor multivibrators so as to provide for frequency control of these circuits by means of a low-level dc control signal. Using two well-known types of such inverter circuits as examples, this paper describes the basic principles involved in this frequency control technique and discusses the operation of two test circuits. A primary advantage of this frequency control method is its physical simplicity and low cost. View full abstract»

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  • Static DC to sinusoidal AC inverter using techniques of high-frequency pulse-width modulation

    Page(s): 250 - 256
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    A dc to sinusoidal ac inverter is described in which high-frequency pulse-width modulation is used to provide a low-frequency sine-wave output without the need for either a low-frequency power transformer or for low-frequency filter components. The inverter is physically simple and has low weight and small size. From a practical viewpoint the usefulness of this inverter is further enhanced by its self-regulating property. An analysis of this circuit and its output waveform is also given which provides the mathematical basis for the experimentally observed test results. In addition to the proof of the self-regulating property, it is further proven analytically that the amplitudes of the harmonics of the sinusoidal output voltage are very small with respect to the amplitude of the fundamental voltage. View full abstract»

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  • High-power step recovery diodes and saturable inductors in radar pulse modulators

    Page(s): 256 - 260
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    Step recovery diodes are characterized by two distinct reverse recovery phases. During the first phase the minority charge is removed at a low reverse voltage, while during the second phase the reverse voltage builds up rapidly, giving rise to the name step recovery. If such a diode is operated cyclically, the minority charge injected by the forward current is preserved and the minority charge is recovered during the first phase of the reverse recovery interval. This situation is the dual of a nonlinear inductor with rectangular hysteresis loop core material operated cyclically in and out of saturation. Thus, we can use the step recovery diode to construct a pulse compression network which essentially is the dual of the nonlinear magnetic pulse compression network. The nonlinear dielectric pulse compression network which uses step recovery diodes can efficiently generate high-power pulses down to pulse widths of a few nanoseconds. In addition the dielectric network provides much higher pulse compression per stage, thus reducing the volume, weight, and number of components. View full abstract»

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  • Cryotron-based random-access memory

    Page(s): 260 - 267
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    Recent progress in the design of large capacity cryo-electric random-access memories is described. Three-wire cryo-electric memory cells and the hybrid AB system organization which utilizes coincident-current selection are examined from the standpoint of batch fabrication requirements, redundancy, electrical parameters, tolerances, and noise immunity. The advances which have been made with experimental subsystems are described in relation to previous work and are shown to place cryoelectrics as a strong contender in the achievement of a system whose capacity is 108bits or larger. View full abstract»

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  • Flux shuttling--New method for the nondestructive readout of superconductive memory cells

    Page(s): 268 - 271
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    A novel technique for the nondestructive readout (NDRO) of a superconductive memory cell is described. The method is of rather general applicability since it can be utilized for the NDRO of many of the known persistent current cells. A description of the technique in comparison to previous NDRO methods as well as experiments on a memory cell which utilizes this new NDRO technique are discussed. The possibility of using this scheme for random access and associative memories is briefly examined. View full abstract»

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  • Contribution to the use of superconducting shields for magnetic field shaping

    Page(s): 271 - 276
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    The low-field diamagnetism of superconductors has often been used to design quasi-ideal magnetic circuits, especially for traveling wave maser (TWM) magnets. An analogical approach to the calculation of the efficiency of such nonideal cylindrical superconducting shields is presented. In most cases, the problem reduces to a 2-dimensional Laplace equation with given boundary conditions. The logarithmic complex potentiallog (Bx - iBy)has been used to obtain the field homogeneity and disorientation. Partially penetrated shields may be replaced by perfect equivalent ones. The analog measurements on conducting paper permit quick iterations of the solution. Various field component measurements have been done on TWM magnets using bismuth thin film Hall probes and found to be in good agreement with the analog measurements. View full abstract»

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  • An AC quench phenomenon in hard superconducting wires

    Page(s): 277 - 279
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    The process leading to the quench of superconductivity in a nonideal type II superconducting wire carrying an audio-frequency alternating transport current in a normally applied static magnetic field was studied. The quench of superconductivity was found to initiate from particular points of 10-mil diameter Nb25 percent Zr wire in repeated tests. In the course of the experimentation a nucleation site was closely bracketed by potential probes and the voltage response of this segment at currents less than the quench current was studied. Utilizing a limited current density model to describe the ac conduction process, the previous voltage response measurements were used to calculate values for the model parameter Jc. The model was extended to include heating effects and a regenerative process that leads to a quench of superconductivity. Quench current predictions based on voltage measurements prior to the quench at a single frequency agree favorably with measured quench currents over a relatively wide frequency range. 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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Meet Our Editors

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