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Magnetics, IEEE Transactions on

Issue 4 • Date July 1987

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Displaying Results 1 - 12 of 12
  • [Front cover and table of contents]

    Publication Year: 1987 , Page(s): 0
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    Freely Available from IEEE
  • Study of the local structure of metastable crystalline iron-boron alloys

    Publication Year: 1987 , Page(s): 1937 - 1944
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    The microstructure of metastable crystalline Fe100-xBx( 1 \leq x \leq 9 ) alloys, produced by rapidly quenching from the melt, has been studied with different techniques. Studies performed with Möss-bauer effect (ME) spectroscopy and nuclear magnetic resonance (NMR) are reported here, along with preliminary high resolution electron microscopy (HREM) and selected area electron diffraction (SAED) observations, as well as initial extended X-ray absorption fine structure (EXAFS) studies. The alloys, which appeared as bcc single phase upon X-ray diffraction (XRD) analyses, were found to be heterogeneous on a microscopic scale. Both the Mössbauer effect and nuclear magnetic resonance results showed that the alloys could not be considered as random solid solutions of boron in iron. Based on the hyperfine field values at the57Fe,10B, and11B sites, on the relative population of probes at the different sites, and on the temperature dependence of the hyperfine fields, it was concluded that very small regions with an orthorhombic Fe3B-like structure exist in the bulk. The high resolution electron microscopy bright field image observations showed regions 5-15 Å in diameter, embedded in the α-Fe matrix, and having fringe spacings different from those of bcc α-Fe. The selected area electron diffraction patterns contained weak, broad spots which were somewhat more consistent with those from orthorhombic Fe3B than tetragonal Fe3B. The initial extended X-ray absorption fine structure analyses were consistent with the results provided by the other techniques. A comparison is made with a previous description in which these alloys were considered as random solid solutions. Our results are discussed in terms of the short-range order (SRO) for orthorhombic and tetragonal Fe3B, as well as bcc α-Fe. View full abstract»

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  • A study of coercivity in Ca-Ge substituted epitaxial garnets

    Publication Year: 1987 , Page(s): 1945 - 1951
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    This paper is an analysis of two models on the origin of coercivity in certain crystals. The first model, based upon the work of Kersten. suggested that coercivity in soft magnetic materials is due to the variation in domain wall energy throughout the crystal. The second model attributes coercivity to magnetostatic interactions between domain walls and crystal defects. Recent work on calcium and germanium substituted YIG has shown a defect structure similar to the one assumed in both of these models. Introducing the experimentally observed parameters into the models yields calculated values for the coercivity that are very close to the observed value for the magnetostatic model and very poor for the wall energy variation model. View full abstract»

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  • Effects of the heat treatment on the microstructures and magnetic properties in Alnico 5

    Publication Year: 1987 , Page(s): 1952 - 1955
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    In Alnico 5, cooling rate c in a magnetic field from 900°C to 600°C and optimum aging time t at 600°C have the relation of log (t) = 0.417 \log (c) + 0.884 . However the final magnetic properties are highly dependent on the cooling rate. Spinodally decomposed structures of this alloy show that the faster the cooling rate the smaller the size of the FeCo-rich precipitates and the larger the aspect ratio without change of the volume fraction of the precipitates. The length of the long axis of the FeCo-rich precipitates at a given cooling rate is not uniform due to the interconnection of the subsequent precipitates by the magnetic field effect, and this tendency seems to be stronger when the cooling rate is slower. However the length of the short axis of the precipitates is almost the same at a given cooling rate. The length of the short axis l and the cooling rate c in a magnetic field have the relation of \log (l) = 2.385 - 0.317 \log (c) . Optimum solution treatment temperature of the low-temperature treatment method was 860°C. This method has higher coercive force than that of the high-temperature treatment method. The FeCo-rich precipitates of the specimen were aligned more parallel to the applied magnetic field with little interconnection of the precipitates and have a higher aspect ratio than that of the high temperature treatment specimen. View full abstract»

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  • An analytical investigation on the efficiency of a magnetic frequency tripler with series-connected reactors

    Publication Year: 1987 , Page(s): 1956 - 1963
    Cited by:  Papers (2)
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    A numerical analysis of a magnetic frequency tripler with series-connected reactors and the maximum efficiency under the optimum setting of core dimensions is described. The steady-state values of voltage, current, power, efficiency, and power factor are calculated by using the numerical method where the φ-i characteristics of saturable reactor are approximated by a fifth-order polynomial as a function of core dimensions. The core loss, iron loss, and leakage inductance are included in the equivalent circuit for the numerical analysis. The maximum efficiency is obtained by maximizing the performance index which is derived from numerical results for various values of number of turns, air gap length, and core area as parameters. It is analytically shown that the basic tripler circuit without a LC filter achieves such high efficiency as 90 percent and over. The maximum efficiency of the tripler circuit with the LC filter is about 80 percent. View full abstract»

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  • The study of transient current distributions in the conductor of a reactor with laminated core

    Publication Year: 1987 , Page(s): 1964 - 1971
    Cited by:  Papers (1)
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    In this paper, a finite-difference method is used for solving transient electromagnetic field distributions in the conductor of a reactor with laminated core of nonlinear magnetic property. In the analysis, the reactor is divided into iron, air, and copper regions. With the aid of B-μ table and material indexes, both the time-dependent current distribution in the conductor and the vector potential function are obtained. The transient response of the inductance is exhibited in this paper and comparison with steady-state value is made. View full abstract»

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  • The variational treatment of the diffusion equation for vector field problems

    Publication Year: 1987 , Page(s): 1972 - 1977
    Cited by:  Papers (6)
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    A new and efficient technique for the solution of axisymmetric vector potential problems described by the diffusion equation is reported. The equation is solved using the finite element method, and the corresponding element matrices are derived and extensively tested computationally. The numerical results obtained for a simple structure are compared with the exact analytical solution. A difficult problem originating from the area of nuclear power engineering illustrates the application of the method to practial engineering problems. View full abstract»

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  • Three-dimensional field computation of charged sectors: A semianalytical method

    Publication Year: 1987 , Page(s): 1978 - 1984
    Cited by:  Papers (3)
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    An analytical representation of the potential created by charged sectors of a ring has been investigated. The surface charge density of the ring is supposed to be constant along a radius, assuming that a Fourier series development allows simplification into a linear superposition of sinusoidal surface densities. In addition to the obvious electrostatic devices, this approach also applies-because of the similarity of the magnetic equations-to permanent magnets with a uniform magnetization. Laplace's equation is solved by means of separation of variables. A Hankel transform, followed by a numerical integration of a Laplace transform, leads to the identification of the coefficients. Most generally, this integration involves elliptic functions which allow a fast and precise numerical treatment. At any point in space, the potentials are computed with the same simplicity and nearly the same accuracy. The proposed method introduces no systematic error and requires only a small memory-size desk computer. It is also much faster than purely numerical methods such as FEM or FDM; any change in the geometrical dimensions can also be achieved without previous reconditioning. The results of this method compare favorably with those already obtained for homopolar distributions and also with previous experiments on an eight-pole-pair distribution of magnets. View full abstract»

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  • High coercivity sputter-deposited maghemite thin-film disk

    Publication Year: 1987 , Page(s): 1985 - 1994
    Cited by:  Papers (4)
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    The fabrication and read-write characteristics of a high-coercivity sputter-deposited maghemite (γ-Fe2O3) thin-film disk medium is discussed. By employing a low sputtering gas pressure, severe internal strain is introduced into the films. This internal strain markedly increases coercivity. Furthermore, the films are composed of fine crystallites (300-400 Å in diameter), which result in extremely low media noise. A high coercivity (1060 Oe) γ- (Fe0.954Co0.02Ti0.02Cu0.015)2O3thin-film disk medium with a thickness of 0.095 μm exhibited superior read-write characteristics (e.g., a 2493 FRPM recording density D50and a 42 dB signal-to-noise ratio). These results show that sputter-deposited maghemite films have a promising potential for use as high-density disk media. View full abstract»

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  • Reciprocity principles for magnetic recording theory

    Publication Year: 1987 , Page(s): 1995 - 2002
    Cited by:  Papers (9)
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    A generalized reciprocity principle for the theory of magnetic reproduction is rigorously derived from first principles. Flux contributions from head nonlinearities, self-inductance, eddy currents, and radiation are naturally included. Approximations necessary to reduce the general result to several practical forms are clearly demonstrated. An energy interpretation of reciprocity formulas is also discussed. View full abstract»

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  • [Back cover]

    Publication Year: 1987 , Page(s): 0
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    Freely Available from IEEE
  • On damped gyromagnetic precession

    Publication Year: 1987 , Page(s): 2003 - 2004
    Cited by:  Papers (12)
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    The relationship between the two damped gyromagnetic equations in current use is discussed in a novel way. As was concluded thirty years ago, the underlying physics is different even though the equations can be cast with the same mathematical form. 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.

Full Aims & Scope

Meet Our Editors

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