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Influence of Magnetic Field on Dielectric Breakdown in Transformer Oil Based Ferrofluids

100%
Rajňák M., Dolník B., Marton K., Tomčo L., Molčan M., Kopčanský P., Timko M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
248-249
EN
In this paper the experimental study of the breakdown field strength in a transformer oil based ferrofluid is reported. The experiments are conducted on five ferrofluid samples with different magnetic volume fraction. The influence of external magnetic field on the breakdown field strength is investigated, when a quasi-homogenous magnetic field was applied in parallel and perpendicular configuration in regard to the electric field. The obtained results are analysed in accordance to the electron charging of ferrofluid nanoparticles theory.
2
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Dielectric Properties of Magnetic Liquids in High Electric Fields

100%
Herchl F., Kopčanský P., Timko M., Koneracká M., Marton K., Kolcunová I., Tomčo L.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
569-572
EN
In this work, dielectric properties of magnetic fluids composed of magnetite particles dispersed in transformer oil and subjected to a uniform magnetic field were investigated at the high alternating electric field intensities in the range of 0.5-2.5 MV/m. Dielectric stability of the magnetic fluid with the particle volume concentrationΦ= 0.0019 was observed. The magnetic fluid with the concentrationΦ= 0.019 showed the significant changes of permittivity and dielectric losses, too.
3
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Hall Effect in ZnO Extrinsic Structure

84%
Dolník B., Kurimský J., Marton K., Kolcun M., Tomčo L., Briančin J., Fabián M., Halama M., Vojtko M., Rajňák M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
76-77
EN
Zinc oxide-based extrinsic composite was investigated. The sample was selected from a series of components of one production batch, prepared by standard sintering technology. The content of extrinsic elements in ZnO base was determined by SEM. Van der Pauw method with four-point electrode fixture was used for study of conducting phenomena in square-shaped sample. It is normaly preferred to assume the symmetric uniformity of the electrical properties of sample, for which sheet resistance, bulk resistivity and Hall mobility, sheet carrier density and carrier concentration can be calculated. When the uniformity of measured parameters is breached, the anisotropy in the arrangement of the internal structure may be the cause. There remains the question of whether the extrinsic ZnO material can be isotropic, regarding the electrical conductivity. Although the Hall effect has been measured, preliminary measurements indicate the presence of anisotropy in the measured samples. Before measurement the following phenomena should be taken into account: magneto-electric effect, photo-electric effect and the isothermal condition should be preserved. Paper discusses the uniformity deviations for the defined setup configurations for positive and negative magnetic field directions. Bulk resistivity has been calculated by numerical solution of van der Pauw equation. Large offset voltage during the measurement is discussed.
4
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The Investigation on the E-J Characteristics and the Role of Nanoparticle Concentration in Weakly Polar Magnetic Fluids

84%
Kurimský J., Dolník B., Marton K., Kolcun M., Tomčo L., Rajňák M., Timko M., Kopčanský P.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
246-247
EN
The paper presents investigation on the magnetic fluids that are stable colloidal suspensions of single-domain magnetic particles in a liquid carrier of dielectrics nature. Studies were made on the electric field vs. current density, e.i. E-J characterization commonly observed in insulating liquids under uniform low electric or magnetic fields. High performance oil was used as the dielectric carrier. The experiments were carried out at different volume concentrations of magnetite nanoparticles up to 4%.
5
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Magnetodielectric Properties of Transformer Oil Based Magnetic Fluids

84%
Timko M., Kopcansky P., Molcan M., Tomco L., Marton K., Molokac S., Rybar P., Stoian F., Holotescu S., Taculescu A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1253-1256
EN
This contribution is devoted to study of dielectric and magnetodielectric properties in transformer oil based magnetic fluid. The dielectric permittivity and their anisotropy at various mutual orientation electric (50 Hz) and magnetic field were shown at the different volume concentrations of nanoparticles at room temperature. The linear increase of dielectric constant with volume concentration was confirmed which is in good agreement with the theoretical Maxwell prediction. The dielectric anisotropy factor g(B, ω) is very close to g=1. The values of permittivity increased with the increase of volume fraction of magnetite nanoparticles. The highest value of anisotropy characterized by deviation of permittivity Δε=ε_{∥} - ε_{⊥} was found for the highest volume concentration which could mean that no aggregation of magnetite nanoparticles had appeared.
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