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Measurement of Complex Permittivity of Oil-Based Ferrofluid in Magnetic Field

100%
Kúdelčík J., Hardoň Š., Varačka L.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
931-933
EN
The changes of dielectric parameters in oil-based ferrofluid have been measured in an external magnetic field. The frequency dependent real permittivity and the dissipation factor were measured within the frequency ranges from 1 mHz to 2 MHz by a capacitance method. These parameters have been studied in combined electric and magnetic field, when fields were parallel and perpendicular. The Cole-Cole model has been used to analyze measured data. When a magnetic field was applied, the interaction between the magnetic field and magnetic moments of nanoparticles led to the aggregation of magnetic nanoparticles to new structures - thick chains which had influence on the value of dielectric permittivity. At constant magnetic field the dependence of real permittivity and tanδ on angle between the electric and magnetic field (anisotropy) were measured, too. The various influences of magnetic field development on the investigated liquid are discussed.
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Influence of Electric and Magnetic Fields on Dielectric Response of Oil-Based Ferrofluid

100%
Hardoň Š., Kúdelčík J., Bury P., Gutten M.
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EN
The changes in dielectric parameters and structural arrangement of transformer oil based ferrofluid with magnetic nanoparticles upon the effect of an external magnetic field and an electric field were studied by dielectric spectroscopy. The frequency dependence of dissipation factor was measured within the frequency range from 1 mHz to 10 kHz by a capacitance method. In the presence of the magnetic field the interaction between the magnetic field and magnetic moments of nanoparticles led to the aggregation of nanoparticles. The electric field had also effects on the change in the electric dipole moment of particles by transfer of counterions. The observed low frequency relaxation maximum of dissipation factor was explained by Schwarz theory of electric double layer polarization. The shift of this maximum with the intensity of electric was caused by change of relaxation time of the nanoparticles-counterions systems.
3
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Study of Structural Changes of Water-Based Magnetic-Fluid by Acoustic Spectroscopy

88%
Kúdelčík J., Hardoň Š., Bury P., Timko M., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
|
issue 4
919-921
EN
The effect of an external magnetic field on the changes in structural arrangement of magnetic nanoparticles in water based magnetic fluid was studied by acoustic spectroscopy. When a magnetic field is increased, the interaction between the magnetic field and the magnetic moments of nanoparticles leads to the orientation of magnetic nanoparticles and their following aggregation to long chains that cause the increase of acoustic attenuation. The attenuation of acoustic waves measured for jump changes of the magnetic field to 100, 200, and 300 mT at temperature 20°C showed that the changes of acoustic attenuation increased slowly to a stabilized state that after switching off the magnetic field decreased immediately to initial value. The dependence of attenuation of acoustic waves at constant magnetic field on angle between the wave vector and direction of the applied magnetic field (attenuation anisotropy) has been measured, too. The measured anisotropy of acoustic attenuation attested structural changes of magnetic fluid in the magnetic field.
4
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Influence of Temperature on the Magneto-Dielectrics Effect of Oil-Based Ferrofluid

88%
Kúdelčík J., Hardoň Š., Bury P., Timko M., Kopčanský P.
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EN
The effect of temperature on the magneto-dielectrics behavior was studied by dielectric spectroscopy in the transformer oil-based ferrofluid with magnetic nanoparticles upon the effect of an external magnetic field. The frequency dependence of complex permittivity and dissipation factor were measured within the frequency range from 1 mHz to 10 kHz at different temperatures by a capacitance method. The dielectrics parameters were measured as a function of the external magnetic field in the range of 0-200 mT, parallel to the direction of the electric field as a function of temperature in the range of 15-35°C. The interaction between magnetic field and magnetic moments of nanoparticles led to the aggregation of magnetic nanoparticles to new structures which had influence on dielectric parameters. The dependence of these parameters at constant magnetic field on angle between the direction of the electric and magnetic fields (anisotropy) has been measured, too.
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