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1
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The Structural Phase Transitions in 6CB-Based Ferronematics

100%
Tomašovičová N., Koneracká M., Kopčanský P., Timko M., Závišová V., Tomčo L., Jadżyn J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
336-338
EN
The structural transitions in ferronematics based on the thermotropic nematic liquid crystal 4-cyano-4'-hexylbiphenyl were studied. The ferronematic samples were prepared by doping with magnetic suspension consisting of Fe_3O_4 particles (10 nm in diameter) coated with oleic acid as a surfactant with different volume concentrations of magnetic particles (from 10^{-5} to 10^{-3}). Freedericksz transitions were studied in combined electric and magnetic fields. The experimental results indicated soft anchoring with perpendicular initial orientation between the magnetic moment of the magnetic particles and director.
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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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.
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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.
4
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Magnetic-Field Induced Isotropic-Nematic Phase Transition in PDLC Doped with Magnetic Nanoparticles

84%
Mitróová Z., Tomašovičová N., Timko M., Koneracká M., Tomčo L., Jadżyn J., Palewski, T., Kopčanský P., Kovalchuk O.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1299-1301
EN
The paper presents a study of the polymer dispersed liquid crystals that consist of liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanatobenzene (6CHBT) microdroplets dispersed in polyvinyl alcohol and doped with various kinds of magnetic particles. As magnetic nanoparticles there were used single walled carbon nanotubes and magnetite labeled single walled carbon nanotubes. The volume concentration of the particles was 2 × 10^{-3}. Magnetic properties were investigated by a SQUID magnetometer. The higher saturation magnetization has been achieved in sample polymer dispersed liquid crystal doped with magnetite labeled single walled carbon nanotubes. The phase transition temperature from isotropic to nematic phase at the external magnetic field 0 T and 12 T was monitored by precise capacitance measurements in the capacitance cell filled with prepared sample. The significant shift of the phase transition temperature (0.2°C) at the external magnetic field 12 T has been observed in sample polymer dispersed liquid crystal doped with magnetite labeled single walled carbon nanotubes.
5
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The Dynamics of the Soret Effect in Thin Film of Magnetic Fluid

84%
Kopčanský P., Tomčo L., Timko M., Ocelík V., Koneracká M., Turek I., Štelina J., Musil C.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
875-878
EN
The Soret effect in interference field of two intensive laser beams in the thin film of magnetic fluid was used to create a periodical structure of density of magnetic particles. The structures obtained were indicated using the self-diffraction of the optical beam creating the structures. The relaxation phenomena after switching off the laser interference field were discussed in terms of the spectrum of relaxation times. This spectrum is proportional to hydrodynamic particle size distribution. The relaxation of optical grating consists of two well-defined channels, i.e. decay through single particles and small aggregates, respectively.
6
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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.
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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.
7
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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.
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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%.
8
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Dielectric Properties of Lyotropic Magnetic Liquid Crystal

68%
Kopčanský P., Tomčo L., Jadzyn J., Swiergiel J., Majorošová J., Kubovčíková M., Timko M., Rajňák M., Šipošová K., Gažová Z., Bednariková Z., Hu C.-K., Hayryan S., Studenyak I., Kovalchuk T., Kovalchuk O.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
632-634
EN
An important feature of lyotropic liquid crystals is the self-assembly of the amphiphilic molecules as supermolecular structures. We have studied the formation of nematic liquid crystal phase in solutions containing lysozyme amyloid fibrils and magnetic nanoparticles using oscilloscopic method. Interaction of fibrils with magnetic nanoparticles under the external magnetic field resulted in fibril re-arrangement. The analysis of the obtained results suggests that the decrease in conductivity of solutions in presence of magnetic field is due to decrease of the ion mobility caused by re-arrangement of structures in the solution. The obtained results allow determination of the optimum ratio of the components which can lead to preparation of solutions with a more ordered structure in presence of magnetic field.
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