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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.
2
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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
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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.
5
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Structural Changes in Liquid Crystals Doped with Rod-Like Magnetic Particles Studied by Surface Acoustic Waves

76%
Bury P., Veveričík M., Kúdelčík J., Kopčanský P., Timko M., Závišová V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
913-915
EN
The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electric and weak magnetic fields were studied by means of the attenuation of surface acoustic wave of frequency 30 MHz propagating along ferronematic liquid crystals. Three low volume concentrations (Φ=1×10¯⁵, 1×10¯⁴ and 1×10¯³) of rod-like magnetic particles were added to liquid crystal during its isotropic phase. Several measurements including the investigation of the effects of electrical and magnetic fields applied both separately and in conjunction as well as the influence of temperature on the surface acoustic wave attenuation were performed. The distinctive surface acoustic wave attenuation responses induced by both electric and magnetic fields in studied ferronematic liquid crystals have been observed suggesting both structural changes and the orientational coupling between magnetic moments of magnetic particles and the director of the liquid crystal. Obtained results confirmed the significant influence of the presence of magnetic particles on the structural properties and resulting behavior of 6CHBT liquid crystal.
6
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Temperature Effect on the Structure of Transformer Oil Based Magnetic Fluids Using Acoustic Spectroscopy

76%
Kúdelčík J., Bury P., Drga J., Kopčanský P., Závišová V., Timko M.
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EN
The changes in structural arrangement in transformer oil based magnetic fluids upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. The attenuation of acoustic waves was measured as a function of an external magnetic field in the range of 0-300 mT, parallel to the direction of the field and as a function of temperature in the range of 15-35°C for various magnetic nanoparticles concentrations. The strong influence of the steeped magnetic field on the acoustic wave attenuation was detected and its hysteresis was observed, too. When a magnetic field is swept at a constant rate, the dominant interactions between the external magnetic field and the magnetic moment of the nanoparticles occur, leading to the aggregation of magnetic nanoparticles and clusters formation. However, the temperature of magnetic fluids has very important influence on the obtained dependences, where the mechanism of thermal motion acts against the cluster creation. The observed influences of magnetic field and temperature on the investigated magnetic liquids structure are discussed.
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