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Magnetics, IEEE Transactions on

Issue 2 • Date March 1980

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Displaying Results 1 - 25 of 56
  • [Front cover and table of contents]

    Publication Year: 1980 , Page(s): 0
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    Freely Available from IEEE
  • Guest editorial

    Publication Year: 1980 , Page(s): 171
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    Freely Available from IEEE
  • Progress in the development of ferromagnetic liquids

    Publication Year: 1980 , Page(s): 172 - 177
    Cited by:  Papers (1)  |  Patents (3)
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    Factors affecting the stability of suspensions of ferromagnetic particles in non-conducting and metallic liquids are discussed. The preparation and properties of suspensions of Fe3O4particles and metallic particles in various liquids are discussed and the progress in the development of new ferromagnetic liquids reviewed. View full abstract»

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  • Preparation of dilution-stable aqueous magnetic fluids

    Publication Year: 1980 , Page(s): 178 - 183
    Cited by:  Papers (12)  |  Patents (1)
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    As part of its program in advancing mineral technology, the Bureau of Mines, U.S. Department of the Interior, has investigated the production of water-base magnetic fluids that are stable toward dilution, and therefore fit for mineral and material beneficiation. Extension of the Bureau developed peptization technique for kerosine-base magnetic fluids to the preparation of the aqueous variety was possible when oleic acid was replaced by dodecylamine. The fluids thus prepared were, however, not stable toward dilution. Irreversible flocculation followed the addition of excessive quantities of water, such as would be encountered in mineral beneficiation operations. When dodecanoic (lauric) acid was used instead of dodecylamine as the dispersing agent, the resulting aqueous magnetic fluid was found to be more stable toward dilution with water. In this second generation water-base magnetic fluid, the dodecanate anionic dispersing agent is superior to the commonly used dodecylamine cationic dispersing agent. Chemisorption of dodecanate anion on the magnetite surface proper by chemically bonding to surface iron atoms is contrasted to the mere adsorption of a cationic surfactant on the solution side of the electric double layer. Expansion of the double layer by dilution and the accompanying decrease in dodecylamine bulk concentration can detach the cationic dispersing agent from the particles of old generation magnetic fluids and nullify their electrostatic charge. By contrast, the firmly held anionic dispersing agent will continue to adhere to the magnetic particles while augmenting their electrostatic charge. Thus, while the former fluids may irreversibly flocculate, the new generation fluids will resist flocculation upon dilution. View full abstract»

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  • Properties of magnetic fluid particles

    Publication Year: 1980 , Page(s): 184 - 190
    Cited by:  Papers (6)  |  Patents (1)
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    Very fine particles of magnetite, nickel ferrite, and cobalt ferrite were produced by grinding coarser powders in a ball mill with a carrier fluid and a surfactant. The particles were examined by means of chemical analysis, electron microscopy, x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. Properties were determined before and after removing the surfactant coating. The most significant observation was that in some systems a large fraction of the spins was pinned in extremely high anisotropy fields as a result of bonding to the surfactant molecules. Anomalous magnetic hysteresis behavior was also noted when the surfactant coating was present. View full abstract»

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  • Aggregate formation in metallic ferromagnetic liquids

    Publication Year: 1980 , Page(s): 191 - 196
    Cited by:  Papers (1)  |  Patents (1)
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    Ferromagnetic liquids containing 45A diameter tin or antimony coated iron particles dispersed in mercury have been prepared electrolytically. The fluids are found to have a magnetisation which is time dependent when an applied field is abruptly reduced. The characteristic decay time which is of the order of 60s cannot be attributed to magnetisation changes due to small noninteracting particles of 45A diameter but it is consistent with the presence of particle aggregates of 104A diameter. Measurements of sedimentation rates and viscosity are also consistent with the presence of aggregates of 104A diameter. Measurements of the sedimentation rate in a gravitational field show that if the particles are coated with tin and particularly antimony fluid stability is improved and aggregate size reduced. It is suggested that particle aggregation may be prevented by ensuring that the liquid contains a distribution of particles with a median diameter appreciably smaller than 45A and a small standard deviation. View full abstract»

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  • Concentration-dependent correlations in ferrofluids studied by small-angle scattering of synchrotron X-radiation

    Publication Year: 1980 , Page(s): 197 - 202
    Cited by:  Papers (4)
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    Small-angle X-ray scattering has been used to study correlations between the magnetic grains of ferrofluids : for dilute colloïids, the grains look isolated or associated in dimers, trimers, etc ... depending on the nature of the ferrofluids. At higher concentration, an order appears in the spatial distribution of the grains even without magnetic field. The application of a magnetic field can generate alongated fibers of grains. An average interfiber spacing has been put in evidence. Small-angle X-ray scattering reveals as a sensitive quality test of the grain agglomeration in ferrofluids. View full abstract»

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  • Scattering and polarization of light by magnetic fluids

    Publication Year: 1980 , Page(s): 203 - 206
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    Expression for the intensity and the degree of polarization of light scattered by a magnetic colloid are derived. Experimental results obtained by earlier investigators are discussed on the basis of these expressions. View full abstract»

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  • Continuum mechanics of a magnetically saturated fluid

    Publication Year: 1980 , Page(s): 207 - 210
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    The physical properties of a magnetically saturated fluid are well accepted. This work is concerned with its continuous description. Using global balance law approach we first derive the differential equations and boundary conditions for continua with internal rotations of hydrodynamic as well as of magnetic origin. The constitutive relationships are then introduced which together with the foregoing equations lead to a complete set of equations for the study of magnetomechanical fluid problems. View full abstract»

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  • Theory of ultrasonic attenuation in magnetic fluids

    Publication Year: 1980 , Page(s): 211 - 213
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    Recent ultrasonic measurements have yielded anomalous results for the velocity and attenuation in magnetic fluids as a function of the applied field. Thus far, the experimental results have not been satisfactorily explained by a theoretical model. In the present paper, starting with Tarapov's ferrohydro-dynamical equations, we attempt to derive an expression for the ultrasonic attenuation. Numerical calculations, with adjustable parameters, give fairly good agreement between theory and experiment for attenuation versus field angle. View full abstract»

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  • Mathematical theory of non-linear waves on the surface of a magnetic fluid

    Publication Year: 1980 , Page(s): 214 - 220
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    Consider a ferrofluid occupying the region z \leq 0 . If the fluid is subjected to a sufficiently strong magnetic field, surface waves appear. Under certain assumptions we shall prove that when the field strength becomes greater than a critical strength, a nontrivial wave solution on the surface of the ferrofluid bifurcates from the trivial solution. We then study the stability of these nontrivial solutions. View full abstract»

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  • The origin of magnetic birefringence and dichroism in magnetic fluids

    Publication Year: 1980 , Page(s): 221 - 225
    Cited by:  Papers (9)
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    The optical birefringence and dichroism observed in magnetic fluids when subjected to a magnetic field are generally ascribed to orientation of the particles, to anisotropic spatial ordering, or to string formation. Magnitude, concentration- and time dependence of the anisotropies predicted by these mechanisms are compared with the available experimental data. This leads to the conclusion that orientation of small aggregates and secondary aggregation of large aggregates into strings are the most likely cause of the large anisotropies. Orientation of single particles can be responsible for small anisotropies only. Field-induced spatial ordering has, at least optically, not (yet) been observed. View full abstract»

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  • New phenomena in barbotage and sedimentation in magnetic fluids

    Publication Year: 1980 , Page(s): 226 - 232
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    New multivelocity model was deduced for a dispersive magnetizable medium: magnetic fluid - gas bubbles or solid particles. Resulting equations may be used for discribing the processes of concentration, separation and barbotage. The characteristics of deduced set were examined. The problem was solved concerning floatation and sedimentation of particles or babbles in a magnetic fluid in a solenoidal magnetic field. View full abstract»

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  • Phase diagrams of model magnetofluids

    Publication Year: 1980 , Page(s): 233 - 236
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    A model of ferrofluids is treated analytically and numerically in order to discuss the phase diagrams. Magnetic particles are supposed to sit on a lattice and to interact through a magnetic Kac potential and through a short range potential between nearest neighbours. The equation of state and the phase diagrams of such one and two dimensional ferrofluids are presented and discussed. View full abstract»

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  • Experimental investigations of magnetic fluids

    Publication Year: 1980 , Page(s): 237 - 250
    Cited by:  Papers (8)
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    First Page of the Article
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  • Review of agglomeration in ferrofluids

    Publication Year: 1980 , Page(s): 251 - 253
    Cited by:  Papers (2)
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    Ideally, magnetic colloids have sufficient surfactant and thermal agitation to prevent the agglomeration of the particles. However, agglomeration has been observed in light scattering, light microscope observations, pulsed magnetization measurements, and gravitational settling experiments. Agglomerate sizes have ranged from a chain of a few particles to ellipsoidal clumps of more than 1010particles. The agglomeration appears to be reversible and strongly dependent upon the applied magnetic field and the particular ferrofluid. Theoretical approaches are based either on equilibrium statistical mechanics (for small agglomerates) or on a) minimizing the energy per particle and b) calculating a critical hydrodynamic shear stress (for large agglomerates under gravitational settling). We review the experiments, the theories, and some areas for future research. View full abstract»

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  • Dielectric behaviour of a ferrofluid subjected to a uniform magnetic field

    Publication Year: 1980 , Page(s): 254 - 257
    Cited by:  Papers (5)
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    The electric susceptibility of samples of ferrofluids subjected to a uniform magnetic field H was measured. The electric susceptibility \chi is dependent on the magnitude of the magnetic field and on the relative direction between the electric field E and the magnetic field H . 1) When E is perpendicular to H, frac{\partial \chi _{\perp }}{\partial H} < 0 2) When E is parallel to H, frac{\partial \chi _{parel\lel}}{\partial H} > 0 These results have been interpreted as a magneto-electric directive effect. A model is proposed, based on the assumption that the magnetic particles are roughly ellipsoidal and conducting grains. View full abstract»

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  • Inversion in magneto-optical effects

    Publication Year: 1980 , Page(s): 258 - 261
    Cited by:  Papers (2)
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    Magnetically induced birefringence and dichroism in certain colloidal suspensions exhibit inversion in sign of the effect. The paper discusses various mechanisms which may give rise to such effects. Methods are suggested to trace origin of such inversions. Certain theoretical and experimental results are also discussed. View full abstract»

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  • New determination of the liquidus line of AuCo by magnetic measurements

    Publication Year: 1980 , Page(s): 262 - 265
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    Magnetic measurements of Au-Co alloys at high temperatures are presented. They prove that Au73Co27 is not the eutectic alloy but a hypereutectic one; the phase diagram is corrected and the eutectic composition is determined: 24.2 ± .2 at. % Co. Magnetic measurements of the eutectic alloy indicate the existence of small Co-clusters in the liquid state only a few degrees above the eutectic temperature. View full abstract»

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  • Ferronematic lyotropic

    Publication Year: 1980 , Page(s): 266 - 269
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    Combination of ferrofluids and liquid crystals has been possible using a nematic lyotropic phase which is an aqueous micellar system and a water base ferrofluid. A stable product results which can be oriented in magnetic fields of several Gauss, i.e. 103times lower than for the initial liquid crystal. Cholesterization has been possible on the same material. View full abstract»

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  • The Landau and Lifshitz hydrostatic "pressure" p(ρ,T) exemplified by thought experiments

    Publication Year: 1980 , Page(s): 270 - 274
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    The density-related, Landau and Lifshitz hydrostatic "pressure" p(ρ,T), appearing in the modern literature on the stresses in polarizable fluids, and known also as the Abraham-Becker hydrostatic "pressure", is examined in a thought experiment. Fluid in a rectangular channel is put through a cyclic magnetization and dilatation process at constant temperature. A very direct solution for p(ρ,T) is obtained using the concepts of lumped-parameter electromechanics. The properties of this "pressure" as a carrier of density information and as a contributor to the stresses are illustrated. View full abstract»

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  • Stability of magnetic fluid penetration through a porous medium with uniform magnetic field oblique to the interface

    Publication Year: 1980 , Page(s): 275 - 282
    Cited by:  Papers (1)  |  Patents (1)
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    Recent work has shown that the fingering instability, which develops when a more viscous fluid is pushed through the voids of a porous medium or through a Hele-Shaw cell by a less viscous fluid, can be prevented if a magnetic field is applied tangential to a flat fluid interface separating magnetizable and non-magnetizable fluids. This earlier work is extended here by considering equilibrium magnetic field components both perpendicular and parallel to the flat interface. The tangential field component stabilizes those waves traveling along the field lines while the normal field is destabilizing. The analysis is developed through a general set of relations for perturbation field and flow interfacial variables defined for a "prototype" magnetizable fluid layer which can be used to describe the small signal stability characteristics of layered fluid systems. In a uniform tangential magnetic field geometry, experimental results of the most unstable wavelength in a Hele-Shaw cell are shown to agree well with theory. View full abstract»

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  • Ferrofluid flow under the influence of rotating magnetic fields

    Publication Year: 1980 , Page(s): 283 - 287
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    Experimental data are presented concerning the physical mechanism of the electromagnetically induced macroscopic rotation of ferrofluids. The rotating velocity distributions, determined using a DISA anemometer equipment and a tensometric transducer system, showed a very different behaviour of ferrofluids in a low frequency (0 + 10 Hz) rotating magnetic field in comparison with that observed in the higher frequency region ( >15 Hz). The data are compared with other experimental and theoretical results. View full abstract»

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  • Instabilities of magnetic fluids leading to a rupture of continuity

    Publication Year: 1980 , Page(s): 288 - 297
    Cited by:  Papers (1)
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    In the present paper attention is focused on topological instabilities of magnetic fluids. The authors review various studies concerned with the magnetic fluid instabilities leading to disintegration of the initial fluid volume. View full abstract»

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  • A dissipative process in ferrofluid in non-homogeneous magnetic field

    Publication Year: 1980 , Page(s): 298 - 300
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    Equations of motion of ferrofluid in non-homogenious magnetic field are derived, and it is shown that due to the orientational relaxation of suspesion particles, additional dissipative terms appear in this equations proportional to the velocity and the angular velocity of ferrofluid. Additional kinetic coefficients are found as functions of magnetic field and temperature by means of the approximate solution of rotational Fokker-Plank equation. 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