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Magnetics, IEEE Transactions on

Issue 1 • Date March 1971

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Displaying Results 1 - 25 of 30
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Editorial

    Page(s): 3
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    Freely Available from IEEE
  • Saturation magnetic recording process

    Page(s): 4 - 16
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    This review of the saturation magnetic recording process is tutorial in approach. The emphasis throughout is on the development of intuitive understanding as well as the development of a first-order analysis (good to 10-20 percent) of the process. By means of treating two different functional approximations to the magnetization distribution in the medium, linear and arctangent, it is shown that the peak output voltage and half-amplitude pulse width of a transition are nearly independent of the distribution. Thus good estimates of these important system parameters may be made without reliance upon a specific model. It is made apparent that head-to-medium spacing and effective-medium thickness are of dominant importance in system density considerations. View full abstract»

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  • Pulse transformers

    Page(s): 17 - 28
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    Pulse transformers capable of transmitting substantially rectangular voltage pulses, with durations of less than one microsecond, were developed for radar applications during World War II. Their primary functions were to match the impedances of high-power microwave radio-frequency electron-tube generators to electronic pulse generators and coaxial transmission cables, and to provide polarity reversal and impedance matching functions within pulse generator circuitry. The principle contributor to the development of satisfactory pulse transformers was the development of cores of thin-gauge magnetic materials having 1 μs pulse permeabilities in the range of 500 to 3500 for flux-density changes of 10 000 G. The development of void free dry-type insulation systems made it possible to produce dry-type pulse transformers for operation at pulse voltages below 12 kV. The pulse transformer development work was paralleled by analytical work which enabled pulse transformer designers to make designs to meet the requirements of the radar circuit designers. The analysis relates the three principle pulse transformer parameters, which are magnetizing inductance, leakage inductance, and effective distributed capacitance, in combination with the circuit parameters which are source resistance, effective load resistance, and load shunt capacitance, to the rise time, top ripple and droop, and fall time of the output pulse. Pulse transformers now cover a wide range of sizes and power levels and pulse widths. Small units in computer applications may deliver only a few volts at pulse widths less than 0.1 μs. Large units in linear accelerators, however, may deliver pulse powers of 70 MW at 270 kV with a pulse width of about 3 μs. View full abstract»

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  • Magnetostrictive phenomena in metallic materials and some of their device applications

    Page(s): 29 - 48
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    The phenomenon of magnetostriction, or the change in a body's dimensions during the magnetization process, was first reported by Joule. Since then, the interaction between strain and the magnetization process has been studied extensively, particularly in the magnetic metals and alloys that have been found to be of technological importance. The purpose of this paper is to review magnetostrictive phenomena in metallic materials and to discuss a number of devices making use of magnetostriction. After presenting some fundamentals of magnetostriction, a review is given of magnetoelastic effects and magnetoelastically induced anisotropies in magnetic films. Some of the domain patterns and domain visualization techniques that have been found to be related to the magnetostrictive properties of magnetic materials are discussed. The application of magnetostrictive materials to memory devices is reviewed. Included are such areas as magnetostrictive delay lines, ferroacoustic memories of both the flat film and wire type, thermo-strictive recording, and fiat film displays and display memories. View full abstract»

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  • Iron and silicon-iron alloys

    Page(s): 48 - 60
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    The principal soft ferromagnetic materials in use today are still iron and silicon-iron alloys. Factors affecting magnetic properties of importance in practical use are evaluated and related to properties attainable in iron and electrical steels. Developments in metallurgy and technology leading up to the present status of com-merical materials in the principal categories of iron, low-carbon steel, nonoriented silicon-iron and grain-oriented silicon-iron are described. Improvements in magnetic properties have been achieved primarily by minimizing chemical impurities and controlling crystal orientation. The relation of material properties to applications is discussed and an evaluation of possible future developments is made. View full abstract»

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  • Magnetic materials analyses by nuclear spectrometry: A joint approach to Mössbauer effect and nuclear magnetic resonance

    Page(s): 61 - 91
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    The common physical basis of the Mossbauer effect (ME) and the nuclear magnetic resonance (NMR) methods is shortly reviewed by discussing the relevant physical properties of nuclei and the interactions of atomic nuclei with electric and magnetic fields. A survey is given of the measurement methods. In principle all those properties of materials can be measured by ME and NMR which influence the energy levels of atomic nuclei and change the shape and intensity of ME and NMR spectra. These properties include the magnetic hyperfine field present in magnetically ordered materials, the valency state of atoms influencing the charge density at the nucleus, the local symmetry of the neighborhood of an atom resulting in electric field gradients at the nucleus, etc. Macroscopic properties connected with these microscopic properties are the magnetization, the magnetic, electric and structural order of crystals, lattice imperfections, and size, shape, and texture of crystallites. Most of these physical properties are closely related to the magnetic properties of matter. Both ME and NMR are limited to specific isotopes and therefore only special groups of' materials are accessible for investigation by these methods. Extensive data about NMR investigations on these materials in the last five years and complementary information about ME investigations on these materials are presented in tabular form and are discussed for selected examples. View full abstract»

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  • Soft magnetic structural alloys for elevated-temperature applications

    Page(s): 91 - 102
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    Metallurgical efforts to develop a soft magnetic material suitable for application in the rotor of a generator or motor in advanced aerospace electric systems are reviewed. Commercial materials which have been considered include AISI 4340 steel, H-11 steel, Nivco alloy, and 15- and 18-percent Ni maraging steels. Developments described have led to several new materials with combination of good mechanical and magnetic properties at elevated temperature. Such materials include an improved maraging steel a precipitation hardenable cobalt-base alloy, a carbide strengthened Co-W alloy, dispersion-strengthened soft magnetic alloys, and unidirectionally solidified Co-Nb-Fe eutectic alloys. View full abstract»

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  • Review of magnetic properties of Fe-Ni alloys

    Page(s): 102 - 113
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    During the past two decades, improved understanding of the fundamental magnetic behavior of Fe-Ni alloys has made them one of the most versatile class of soft magnetic materials. No longer is the concern limited to high permeability and low coercfve force at room temperature. Alloys have now been custom-crafted to meet high permeability requirements at cryogenic temperatures, exhibit a skewed hysteresis loop for pulse transformer use, or a square hysteresis loop combined with stress insensitivity and controlled coercive force for memory applications. These examples are discussed in terms of the relationship of magnetic properties to structure and composition in Fe-Ni alloys. View full abstract»

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  • Magnetomechanical effects in the Rayleigh region

    Page(s): 113 - 133
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    A brief résumé of basic magnetism is followed by a consideration of the magnetization process in the absence of applied mechanical stress, in which the importance of internal stresses and inclusions is emphasized and which leads to the introduction of Néel's disperse field theory. The Rayleigh laws are interpreted in terms of "Preisach loops." Early work on the influence of stress on the magnetization process is discussed, leading on to a detailed consideration of this phenomenon in terms of three mechanisms which, for simplicity, are taken to be essentially distinct. These are, first, the alteration of the pressure on 90° domain walls by the application of stress; second, the alteration in the opposition term, which must clearly be in balance with this pressure for domain-wall equilibrium, and, finally, large-scale alterations in the overall domain structure. Existing experimental observations, on both magnetically soft and hard materials, are interpreted in terms of these three mechanisms. View full abstract»

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  • Parametric generation of acoustic waves and mode-locking of spin waves through magnetoelastic coupling

    Page(s): 133 - 137
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    A YIG disk with parallel and polished surfaces was bonded onto a quartz rod with a transducer attached to it. The YIG sample was placed in a microwave cavity in a parallel-pumping configuration. For microwave power several decibels above the threshold for spin-wave instability, parametric generation of low-frequency acoustic waves was observed, and was accompanied by the simultaneous appearance of low-frequency modulation of the microwave reflected power. The effects were attributed to the beating of spin-wave side bands with the central band. The existence of side bands was confirmed by measuring the spin-wave spectrum. In the mode-locking experiment, a low-frequency acoustic wave was sent into the YIG sample through the transducer. Experimental evidences show that the acoustic wave, through magnetoelastic coupling, not only locks the phase but also enhances the amplitude of the sidebands relative to the central band. View full abstract»

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  • Acoustic Faraday rotation

    Page(s): 138 - 141
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    In ferrimagnets, under a dc magnetic field, magnon-phonon coupling can result in such effects as acoustic birefringence and Faraday rotation. From our work on acoustic Faraday rotation in nonellipsoidal samples of YIG, we found three regions of rotation. The low field region has an internal magnetic field insufficient for effective phonon-magnon conversion. Fitting the rotation observed to the theory we find values for the second magnetoelastic constant and the average demagnetizing field. Between the low and middle field regions a decrease in the amplitude of the transmitted elastic wave was observed and attributed to spin-wave losses. The middle field region was characterized by conversion of elastic energy into spin waves. Regions of inefficient conversion were observed. Faraday rotation was again observed in the high field region. View full abstract»

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  • Stroboscopic observation of cylindrical domain propagation in a T-bar structure

    Page(s): 142 - 145
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    A technique of stroboscopic observation has been applied to the examination of the dynamic behavior of cylindrical magnetic domains, in a single crystal platelet of Sm0.55Tb0.45FeO3, propagating around a closed path Permalloy film T-bar structured overlay. Domain propagation is achieved by means of the time-varying magnetic pole configuration induced by a rotating magnetic field in the plane of the Permalloy film. Semiquantitative measurements under conditions of continuous propagation show instantaneous wall velocities varying from almost zero to greater than six times the time-averaged domain velocity. The speed of propagation in this T-bar structure is limited by the design of the comer where domains become trapped. The stroboscopic technique used here should find important application in the dynamic evaluation of designs for domain-propagation structures. View full abstract»

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  • Integrated magnetic recording heads

    Page(s): 146 - 150
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    A new type of integrated magnetic recording head has been developed. The head is made completely from thin films by vacuum deposition through a mask. This technology enables us to make many heads in one vacuum cycle. A special study has been carried out on the geometrical forms and on the anisotropic magnetic material. The demagnetizing fields require that we make magnetostatic coupling layers for each magnetic leg of the head. Also, the results indicate that the heads can be used for writing and reading. View full abstract»

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  • A magnetoresistive readout transducer

    Page(s): 150 - 154
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    A new type of reproduce transducer for reading magnetically recorded tapes is described. The device structure, which utilizes the magnetoresistive effect in a thin magnetic film deposited onto a nonmagnetic substrate, provides wavelength response characteristics comparable to existing technology. Indigenous noise effects are subordinate to tape noise. No intrinsic frequency limitations are experienced for recording bandwidths in existence today. Since the device detects the tape's fringing fields directly, the output is not a function of tape velocity. The device construction lends itself nicely to multichannel head assemblies. The transducer may also be used to detect digitally recorded information. View full abstract»

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  • Polymer-coated metal and alloy particles for magnetic recording

    Page(s): 155 - 158
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    Fine particles of cobalt and an iron-cobalt alloy were prepared and encapsulated in a plastic film to protect them from oxidation. The magnetic properties of the coated powders were determined and compared with the properties of coated iron powders studied previously. The thermal degradation of magnetic properties was also investigated. Polymer-coated iron and cobalt powders were incorporated in a Hypalon rubber matrix to obtain additional magnetic property data and to study recording characteristics. The experimental materials exhibited better high-frequency response in magnetic recording than a standard γ-Fe2O3material, and one material had a higher signal output as well. View full abstract»

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  • Calculations of external bit fields

    Page(s): 158 - 162
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    The amplitude and distribution of the external fields emanating from recorded transitions are of great interest to technologists in the field of information storage and retrieval and, more particularly, to those studying alternate readout techniques to the conventional inductive readout method. Such areas include the magnetic transfer process, Hall probe techniques, and the magneto-optic and Lorentz beam readout techniques. In this paper we used a harmonic analysis simulation of the non-linear digital recording process, and calculated the amplitude and distribution of external bit fields for a wide range of media magnetic properties and thicknesses, and as a function of bit density and spacing above the surface of the media. Justification for using the harmonic analysis model is based upon the good agreement obtained with the reported spatial behavior of the external bit fields measured directly by a scanning electron microscope. In addition, calculations based on simpler models of a line, step, and linear transition show that the harmonic model is a superior first-order approximation of the nonlinear nature of digital magnetic recording. View full abstract»

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  • Change of RF susceptibility and parametric oscillations of the magnetization of stripe films in magnetic fields normal to the surface

    Page(s): 163 - 165
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    Multidomain ferromagnetic resonance (FMR) for Permalloy magnetic fills (thickness 2700 Å) 83 percent Ni with rotatable anisotropy was experimentally observed with an external magnetic field applied normal to the sample surface. The lower frequency branch of multidomain FMR was excited when the RF magnetic fieldhwas oriented along the film plane; forhoriented parallel to the fieldH_{perp}the higher frequency branch was excited. The dependence of the resonant fieldH_{perp}on the frequency of fieldhfor multidomain and single-domain FMR was determined. Increasing the RF fieldhoriented alongH_{perp}gave rise to oscillations of magnetization with the frequency(1/2)f, wherefis the pumping frequency. The dependence of the amplitude of these oscillations on the strength of the RF fieldhand on the magnetizing fieldH_{perp}was investigated. View full abstract»

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  • Influence of coercive force on low-frequency creep in bloch-wall permalloy films

    Page(s): 165 - 171
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    A very high resolution Bitter pattern technique is used to observe the motion of Bloch walls in Permalloy films excited by slowly rising and slowly falling hard-axis fields. For low coercive force films, the basic motion consists of approximately equal and opposite jumps induced by simultaneous wall structure changes at two transition fields. Net motion begins with the application of small easy-axis bias fields. For high coercive force films, although the wall structure changes continue to occur, the wall jumps and a net displacement do net occur until the easy-axis bias field exceeds a certain critical value which is a function of the wall coercive force. View full abstract»

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  • Magnetization spreading in a thin film memory

    Page(s): 171 - 174
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    The hard axis magnetic field distribution within the uniaxial magnetic film element of a thin film memory device is calculated. In the memory device considered, the driving stripline and magnetic film are located between a magnetic keeper and a conducting ground plane. The difficulty encountered in the keeper-ground plane problem arises from the requirement of satisfying boundary conditions at the keeper and ground plane surfaces simultaneously, or in other words, from considering an infinite set of film and stripline images. A method of solution using Fourier transforms proves satisfactory. The dependence of the magnetic field distribution on the relative position of the elements and on variations in material properties is assessed. View full abstract»

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  • Application of ferrites by electrophoresis process as keepers on printed circuit wiring of thin-film memories

    Page(s): 174 - 179
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    A process for applying coatings to conductive materials by means of electrophoresis has been used for coating ferrites on printed circuit conductors as a magnetic keeper material for cylindrical thin film wire memories. This process is also known as electrocoating when used in this manner. The advantage of this process is the ability to obtain consistently a uniform coating of predetermined thickness and density on parts of any configuration. Another feature of this process is that good adhesion of the ferrites to the conductor is obtained. This is accomplished by use of a heterogeneous nitrogen resin as a suspension media for ferrites in an electrocoating bath The thickness of the coating increased with voltage and the density of the ferrites in the coating was dependent upon the concentration of ferrites in the coating bath. The denser the ferrites the higher the permeability. Word straps on a small piece of tunnel structure were electrocoated. Evaluation of these coatings were made in a cylindrical thin film tester. The keepered word straps had a much wider operating margin and a lower write threshold than unkeepered word straps. Complete units were then selectively keepered by this process and tested. These units were compared to those keepered with ferrite sheets and without keepers. The results of these tests indicated an overall improvement in the performance of the discrete keepered wire memory, i.e., lower word drive current, lower write threshold, improved adjacent bit disturb threshold, and increased output voltage with noise and cross talk levels of the discrete keeper lower than those with sheet keepers. View full abstract»

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  • Some developments of electrodeposited wire analog memory

    Page(s): 179 - 182
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    The basic readout and write-in characteristics of NDRO analog memory elements composed of electrodeposited Permalloy wires were reported previously by the authors. The output signal was the second harmonic voltage of the interrogation sinusoidal-wave field (225 kHz) applied along the hard axis, and the amplitude was proportional to the product of the set flux level and square of the interrogation field. This report deals with some details of the write-in characteristics, linearization of write-in characteristics by a negative feedback circuit, and readout of the stored flux level by a fundamental component of the induced voltage, selection schemes are also discussed for practical use. View full abstract»

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  • A gamma-level portable ring-core magnetometer

    Page(s): 183 - 185
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    A four-transistor circuit is described for a battery operated magnetometer that has 0.1γ resolution using 1-in diameter 4-79 or 6-81 Mo-Permalloy tape cores of 20-40 Mx capacity. The center-tapped drive winding also serves as the sense winding, simplifying the sensor assembly. Some signal-to-noise results are presented to illustrate the fairly wide difference that may exist between cores of the same cross section and to demonstrate the advantage of reducing core area. View full abstract»

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  • Computation and modeling of eddy currents in tape-wound square-loop cores

    Page(s): 185 - 197
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    Eddy currents in tape-wound cores are classified into microscopic and macroscopic eddy currents. The latter, denoted by ie, exists during mode II among three switching modes. Inherent peakdot{phi}versusFfor a highF = F_{D}drive is computed from measureddot{phi}_{m}(F_{D})andphi_{m}(F_{D}), thedot{phi}and φ whendot{phi}is maximum. The expected line density of reversed-domain nucleation centers is computed fromphi_{m}(F_{D}). A switching tape-wound core is equivalent to one with "ferrite-core" characteristics that is loaded by a resistanceR_{e} = dot{phi}/i_{e}. A special computer program was developed to computei_{e}(phi,F_{D})andR_{e}(phi,F_{D}), the higher FD, the wider and lower the resulting U shapedR_{e}(phi). Domain-pattern models are proposed. Accordingly,n_{p}(phi,F_{D})domains in whichphi cdot p(phi,F_{D})is generated are encircled by macroscopic eddy currents wheren_{p} geq 0and1 geq p geq 0. The semiempirical modelR_{e}(phi,F_{D}) = R_{ez}(F_{D})/{1 - [phi/phi_{m}(F_{D})]}, where Rezis Reatphi = 0, is proposed. The functions describingphi_{m}(F_{D})andR_{ez}(F_{D})include a total of five parameters besides. View full abstract»

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  • Measurement of losses in saturated solid magnetic cores

    Page(s): 198 - 201
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    A new method of measuring the losses in saturated solid magnetic cores subjected to alternating magnetization is described. The method is based on the measurement of an alternative Poynting vector in the region between the surface of the iron core and the magnetizing winding. The two constituent components of this power-flow vector are the partial electric field and the magnetic field. A brief description of suitable probes for measuring these two field components and the associated measuring circuit is given. Loss measurements are made on two cores, a long rod, and a toroid; the results are compared with those calculated using analytical and numerical methods and also with those predicted by linear electromagnetic theory. 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