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Magnetics, IEEE Transactions on

Issue 3 • Date May 1987

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

    Page(s): 0
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    Freely Available from IEEE
  • Magnetic interaction between spheres

    Page(s): 1853 - 1855
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    Formulas are given for averaging magnetic fields over a sphere, with a particular emphasis on field due to a second sphere which is homogeneously magnetized. View full abstract»

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  • A new approach to Preisach diagrams

    Page(s): 1856 - 1865
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    Magnetization processes are complex. A simple Preisach diagram can describe only the irreversible component of magnetization. An extended Preisach model is introduced, including a reversible magnetization component given by a Langevin function which describes low-field experimental hysteresis loops very well. A family of anhysteretic curves are shown that are dependent on the amplitude and form of the ac used to generate them and the turning points on theM-Hplane. View full abstract»

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  • Automatic disaccommodation measuring system

    Page(s): 1866 - 1868
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    Magnetic after effect measurement constitutes an advantageous procedure for the investigation of point defects giving considerable information about the crystal lattice dynamics. Unfortunately, most standard measuring methods involve tedious impedance bridges which are not suitable for systematic research. Thus a new automatic measuring system, based on the use of an inductance-capacitance resistorLCRmeter, has been developed with special emphasis on soft magnetic materials. The resolution capability of our system is pointed out by measuring the disaccommodation of a ferrite sample. View full abstract»

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  • Magnetic properties of decarburized steels: An investigation of the effects of grain size and carbon content

    Page(s): 1869 - 1876
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    The effects of carbon on the magnetic properties of steel have been of great interest over the years both because of the great commercial importance of steel and because it is known that carbon is the most important single factor affecting the magnetic properties of steel. Slight changes in the amount and distribution of the carbon content can completely mask any changes due to grain size, stress, and the effects of other impurities. The magnetic properties of several specimens of steel in which the carbon content has been deliberately reduced are investigated so that the more subtle effects on magnetic properties caused by these other factors can be determined. The results presented include magnetic Barkhausen measurements, magnetoacoustic emission measurements, and magnetization data. The grain structure of each specimen was closely monitored and the resulting magnetization data correlated with the microstructure. View full abstract»

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  • Investigation of local events of magnetization reversal in a Nd-Fe-B magnet by use of a Hall-effect microprobe

    Page(s): 1877 - 1880
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    Magnetization processes in a sintered Nd-Fe-B permanent magnet (NEOMAX-35) were examined on a small scale using a Hall-effect microprobe with an active area 75 μm on a side. Probes were made by evaporating bismuth through a stencil mask onto glass slides. Experiments were performed by placing a probe onto the polished pole face of a Nd-Fe-B magnet and inserting the probe-magnet assembly into an electromagnet. Barkhausen steps, indicating rapid domain wall motion, were observed (superimposed upon the blank probe signal) in the demagnetization of a fully magnetized magnet. Magnetization traces for a thermally demagnetized Nd-Fe-B magnet did not exhibit measurable Barkhausen steps until a field of approximately 1.2 T was applied. The following observations were made for two thermally demagnetized samples which were cycled through minor hysteresis loops (maximum applied field of approximately 2 T). 1) Virgin magnetization traces did not contain measurable Barkhausen steps; however, all other forward and reverse magnetization traces did. 2) The initial reverse magnetization trace exhibited more and larger Barkhausen steps than subsequent traces. 3) Some Barkhausen steps were repeatable, that is, occurring at approximately the same field on each subsequent forward or reverse trace. Hall voltage signals were on the order of millivolts for probe currents of 10 mA. View full abstract»

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  • Calculation of multivalued potentials in exterior regions

    Page(s): 1881 - 1887
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    In magnetostatic and magnetodynamic problems, Ampere's law leads to a multivalued scalar magnetic potential. A method is proposed to calculate this potential through a finite elements program or, in a more efficient way, through a program using a boundary integral method in nonconducting exterior regions. In this case, one has only to define "cutting lines" on the boundary instead of cutting surfaces. Reported here are the results obtained with the three-dimensional eddy-current code Trifou, using the finite element method inside the conductors coupled with an integral method outside, in which the method has been incorporated, for a test model where some global values can be obtained by hand and compared with those obtained by the code. A study of the influence of mesh refinement and of the position of cutting lines is given. Good agreement and numerical stability indicate that the method is operational. View full abstract»

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  • A model of eddy-current probes with ferrite cores

    Page(s): 1888 - 1904
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    A model of a three-dimensional axisymmetric probe coil with a ferrite core in the presence of a conducting half-space (the workpiece) is developed. The half-space is accounted for by computing the appropriate Green's function by using Bessel transforms. Upon introducing equivalent Amperian currents within the core, we derive a volume integral equation, whose unknown is either the magnetic induction field, or induced magnetization, and whose kernel is the Green's function that was previously derived. The integral equation is transformed via the method of moments into a vector-matrix equation, which is then solved using a linear equation solver. This allows the computation of the magnetic induction field within the core, the driving-point impedance of the coil-core combination, and the induced eddy currents within the workpiece. View full abstract»

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  • A simplified analysis for eddy-current speed transducer

    Page(s): 1905 - 1908
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    A simple solution for the boundary value problem of a rotating metallic disk located in front of an exciting permanent magnet is given. A suggested current distribution is used for describing the induced voltage due to the rotation. The application of this transducer for the measurement of the speed of the rotating shaft is also developed. View full abstract»

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  • Magnetic separation in alternating fields

    Page(s): 1909 - 1912
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    An alternating-current (ac) powered high-gradient magnetic separator (HGMS) was compared with a conventional (direct-current powered) HGMS. Over all tested conditions with magnetite/ silica mixtures, the ac HGMS gave significantly higher grades of magnetite in the magnetic product. The probable reason is that the alternating field causes vibration of the bed of particles held on the matrix which dislodges entrapped nonmagnetic particles. This was supported by testing the HGMS with mechanical vibration of the matrix which gave even higher grades than the ac HGMS. A model of grade, based on the probability of void filling, was developed which fitted the grade versus the feed composition data. View full abstract»

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  • Enhancing the transfer of inductive energy to imploding plasma loads with a single-step meatgrinder circuit

    Page(s): 1913 - 1918
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    The transfer of magnetic energy to an uncoupled load inductor using a novel inductive storage and transfer circuit (single-step meatgrinder) is compared with two classical inductive circuits. The first is the inductor-inductor transfer via an opening switch. The second is a transformer circuit where the primary circuit is opened and energy is transfered to the secondary and the uncoupled load. For identical loads the new circuit is shown to provide a 90-percent improvement over the two conventional circuits in energy transferred to the uncoupled load. A low-current low-voltage experiment, where 35.4 percent of the initial inductive energy is transferred to an uncoupled load using the new circuit, is discussed. A physical design for the Air Force Weapons Laboratory Shiva bank, which accounts for voltage holding, coupling, and parasitic inductance in the switches, is also described. View full abstract»

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  • Analysis of medium-garnet interaction in a parallel high-density magneto-optic read head

    Page(s): 1919 - 1922
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    Signal reproduction by the domain pattern in a garnet layer from a magnetic medium, to be used in a magneto-optic readout system, has been analyzed. The results are used to specify garnet material parameter requirements. Observations of reproducing garnet domain patterns are related to the findings of the analysis. Bi-substituted YIG samples resolving about 2 μm2are reported. View full abstract»

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  • Narrow track readout with magnetic garnet film

    Page(s): 1923 - 1927
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    A novel magneto-optic readout head, which utilizes the modulation of width of straight domains in a garnet film in response to the fringing field from the recording medium, was evaluated from the viewpoint of narrow track readout. In a static transfer experiment with a garnet film having a domain width of 2.25 μm, a definite transfer to the garnet film with track widths of 3 μm or less was confirmed. An expression for the modulation degree of the domain width was derived, and its predictions agreed well with the experimental results. In the dynamic readout experiment, a carrier-to-noise ratio of 50 dB was obtained for a trackwidth of 4 μm and a wavelength of 10 μm. The cross-talk was -30 dB when the track-to-track spacing and track width were 10 μm and 5 μm, respectively. From these results the feasibility of narrow track readout based on this head was demonstrated. The readout performance, including the decrease of readable track width, the wavelength and crosstalk, can be greatly improved if a garnet film, having a domain width narrower than that used in this experiment is used together with a high-density recording medium. View full abstract»

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  • Viterbi decoding and the power spectral densities of some rate one half binary DC free modulation codes

    Page(s): 1928 - 1934
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    The Hamming distance properties are investigated, and some experimental results obtained with the following R = 1/2 binary dc free modulation codes are presented: the (b, l, C) = (1, 5, 3) Miller2code and codes with (b, l, C), respectively, (1, 4, 3), (0, 3, 3), and (0, 1, 2). A R = 3/6, (b, l, C) = (0, 3, 2) combined error-correcting/ modulation code is also investigated. State systems, power spectral densities, and the bit error rates after computer simulated decoding of these codes on both the binary symmetric channel and a burst erasure channel are presented. View full abstract»

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  • Recording characteristics of electroless-plated perpendicular media for flexible disks

    Page(s): 1935 - 1936
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    The read/write characteristics of electroless-plated perpendicular magnetic recording media for flexible disks were studied using commercial VHS and 8-mm VTR ring heads. Excellent results were shown for a medium composed of Co-Ni-Re-P plated on a non-magnetic electroless-plated Ni-P layer. A Ni-P underlayer of only 500 Å greatly improved the read/write characteristics of the disk. Reproduced signals over 300 kFRPI were observed for a system using a VHS head, andD_{50} = 134kFRPI was obtained using an 8-mm head. View full abstract»

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  • [Back cover]

    Page(s): 0
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    Freely Available from IEEE

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