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  1. 54 Acta Physica Polonica A

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  1. 6 2018

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  5. 9 2012

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  1. 54 Kopčanský P.

  2. 41 Timko M.

  3. 20 Koneracká M.

  4. 19 Závišová V.

  5. 18 Tomašovičová N.

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1
Content available remote

Study of Structural Changes of Water-Based Magnetic-Fluid by Acoustic Spectroscopy

100%
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.
2
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Study of Magnetic Fredericksz Transition in Ferronematics

100%
Kopčanský P., Koneracká M., Jadżyn J., Czechowski G., Żywucki B.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
437-440
EN
The magnetic Fredericksz transition in ferronematics (thermotropic nematic liquid crystals 7CB and MBBA combined with fine magnetic particles of a size 10 nm) as a function of concentration of magnetic particles was studied by using simple dielectric measurements. The increase of the threshold magnetic field is observed in 7CB based ferronematic while the decrease of threshold field in MBBA based ferronematic is observed when the concentration of magnetic particles is increased. Experimental results are discussed in the framework of Brochard, de Gennes and Burylov, Raikher theories.
3
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The Effect of Polymer Immobilization on Magnetic Properties of Magnetosomes

100%
Timko M., Džarová A., Kovač J., Kopčanský P., Gojzewski H.
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issue 5
995-997
EN
The anisotropy of several PVA/magnetosomes magnetically textured films has been investigated from the point of view of magnetic properties. The thin film synthesized under the influence of a magnetic field (99 mT) shows the typical behavior of an anisotropic material. On sample textured in magnetic field the magnetisation loop measurements were performed in dependence on the direction of the external magnetic field with respect to the texture axis. The results of hysteresis measurements show that the magnetic field applied during the synthesis promotes an orientation of the chains of magnetosomes and permanently textured film is obtained after solidification. The obtained values for magnetic remanence and coercivity were dependent on the external magnetic field orientation and the alignment effect of particle moments may be clearly seen which is in agreement with the theoretical model of magnetic particle chains.
4
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Synthesis and Characterization of Magnetoferritin

100%
Mitróová Z., Melníková L., Kováč J., Timko M., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1318-1320
EN
The paper presents detailed experimental study of synthesis and characterization a bioinorganic magnetic molecule - magnetoferritin. Magnetoferritin with loading of iron ions per protein molecule in the range from 300 to 3000 was prepared. Size distribution analysis (transmission electron microscopy, dynamic light scattering) shows spherical nanoparticles with particle size distribution from 2 to 12 nm, and hydrodynamic diameter from 12 to 25 nm. The thermomagnetic curves measured after cooling the sample in zero field (zero-field cooling) and under the presence of the measurement field (field cooling) show superparamagnetic behavior with the blocking temperature T_{b} from 22 to 60 K and the magnetization loops measured below T_{b} (at 2 K) show the hysteresis with coercive field from 20 to 30 kA/m depending on the concentration of the magnetic nanoparticles.
5
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Study of Composites Consisting of High-T_{c} Superconductor and Fine Magnetic Particles

100%
Timko M., Kopčanský P., Kováč J., Koneracká M., Plecháček V.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
389-392
EN
The composite systems as a mixture of fine magnetic particles of Fe_{3}O_{4} and superconducting powder such as Bi_{1.8}Pb_{0.2}Sr_{2}Ca_{2}Cu_{3}O_{10+x} were prepared. The influence of internal magnetic field (generated by magnetic particles) on the superconducting properties of prepared composites were studied as a function of concentration of magnetic particles and their magnetic state. The observed data both of the shielding and the Meissner effect were compared with corresponding linear combination of pure signals of magnetite and superconductor, respectively. The large differences were observed for demagnetized samples. It means that result must be discussed in the frame of the distribution of internal magnetic field created by the magnetic particles.
6
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Influence of Temperature on the Magneto-Dielectrics Effect of Oil-Based Ferrofluid

100%
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.
7
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Electro-Rheological Properties of Transformer Oil-Based Magnetic Fluids

87%
Paulovičová K., Tóthová J., Rajňák M., Timko M., Kopčanský P., Lisý V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1141-1143
EN
The aim of this work was to study rheological behavior of nanofluids affected by electric field and temperature. We used transformer oil-based magnetic fluids, the suspensions of permanently magnetized colloidal particles (Fe_3O_4) coated by a stabilizing surfactant and immersed in transformer oil. The rheological characterization of transformer oil-based magnetic fluid was performed using the rotational rheometer MCR 502 in the shear rate from 10 to 1000 s¯¹.The strength of electric field was changed in the interval 0-6 kV cm¯¹. The flow curves and viscosity functions detected at three different temperatures 25, 50, and 75°C disclose rheological characteristics of samples, first of all the viscosity growth under increasing strength of electric field.
8
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Characterization of Carbon Nanotubes

87%
Jeníková M., Zakuťanská K., Kováč J., Girman V., Kopčanský P., Tomašovičová N.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
952-954
EN
The aim of the presented work was to characterize single-walled carbon nanotubes as well as multi-walled carbon nanotubes by transmission electron microscopy, the Raman spectroscopy and magnetization measurements to obtain information about their size, structure, and magnetic properties. We show that having different carbon nanotubes one can easily distinguish the single-wall or multi-wall carbon nanotubes and determine their quality. The obtained results show that carbon nanotubes can be diamagnetic or ferromagnetic depending on their structural parameters.
9
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Temperature Dependence of a Dielectric Relaxation in Weakly Polar Ferrofluids

87%
Rajňák M., Kurimský J., Dolník B., Cimbala R., Paulovičová K., Kopčanský P., Timko M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
943-945
EN
In this paper, we report on the temperature dependent broadband dielectric response of a ferrofluid based on transformer oil and magnetite nanoparticles covered with oleic acid molecules. For that purpose the method of dielectric spectroscopy has been chosen in the frequency range from 20 Hz up to 100 kHz. The experiments were carried out on thin film ferrofluid samples confined in a glass plate capacitor containing indium tin oxide (ITO) plate electrodes. The obtained complex permittivity spectrum shows a pronounced dielectric dispersion in the low frequency range. Taking into account the ferrofluid composition we associate this relaxation with ion impurity polarization at the nanoparticle-oil interface. The strong temperature dependence of the relaxation process has been found when conducting the experiments in the temperature range from 298 K to 358 K. The relaxation time of the revealed process exhibits a typical Arrhenius behavior. Based on the conducted experiments and analysis, we propose some reasonable practical applications of the studied ferrofluid in the field of electrical engineering.
10
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Magnetic Birefringence Study of the Magnetic Core Structure of Ferritin

87%
Koralewski M., Pochylski M., Mitróová Z., Melníková L., Kováč J., Timko M., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1237-1239
EN
Magnetically induced optical birefringence (Δ n) was measured for magnetoferritin and horse spleen ferritin aqueous suspensions. The Δ n for magnetoferritin was described in the frame of the Langevin formalism taking into account distribution of core diameter. The established average magnetic dipole moment and core diameter is equal to about 460 μ_{B} and 3 nm, respectively. It was shown that magnetic birefringence and the Cotton-Mouton constant can be powerful parameters in identification of the magnetic core structure of ferritin, especially useful in biomedicine.
11
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The Influence of Magnetic Particles on the Nematic Droplets Formation in Liquid Crystal

87%
Majorošová J., Gdovinová V., Tomašovičová N., Juríková A., Závišová V., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
955-957
EN
In this work the thermotropic nematic liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanato-benzene (6CHBT) was dissolved in phenyl-isothiocyanate and doped with spherical magnetic particles with volume concentration ϕ₁=10¯⁴ and ϕ₂=10¯³. The influence of the volume concentration on the phase transitions from isotropic to nematic phase was studied by three experimental methods: optical microscopy, differential scanning calorimetry, and dielectric measurements. The obtained results confirmed the coexistence of isotropic and nematic phase, i.e. nematic or ferronematic droplets in isotropic phase in a wide temperature range between nematic and isotropic phase.
12
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The Structural Phase Transitions in 6CB-Based Ferronematics

87%
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.
13
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Thermal Analysis of Magnetic Nanoparticles Modified with Dextran

87%
Juríková A., Csach K., Miškuf J., Koneracká M., Závišová V., Kubovčíková M., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1296-1298
EN
In the work the thermal behaviour of the magnetic nanoparticles modified with polysaccharide dextran of different weight ratios to the magnetite Fe_3O_4 was investigated using thermoanalytical methods - differential scanning calorimetry and thermogravimetric analysis. The adsorption of dextran on the magnetic nanoparticles was confirmed and the influence of the dextran amount in the modified magnetic fluid on the thermal decomposition of the complex system was studied. The results showed that magnetite catalyzed the thermal decomposition of dextran, the adsorbed dextran showed lower initial decomposition temperatures in comparison with the free one.
14
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Thermogravimetric Study of the Decomposition of BSA-Coated Magnetic Nanoparticles

87%
Csach K., Juríková A., Miškuf J., Koneracká M., Závišová V., Kubovčíková M., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1293-1295
EN
Magnetic nanoparticles used in biomedicine have to be biocompatible, which can be achieved by the modification of the magnetic particle surface with an appropriate biocompatible substance. In the work protein bovine serum albumin (BSA) was chosen to modify the surface of magnetic nanoparticles. The BSA-coated magnetic nanoparticles with different input weight ratios of BSA to the magnetite Fe_3O_4 were prepared and thermally characterized using thermogravimetric and differential scanning calorimetric analysis. The adsorption of BSA on the magnetic nanoparticles in wide range of concentration was confirmed. The activation energies of the thermal decomposition of the complex system were estimated.
15
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Magnetic Properties of Encapsulated Magnetite in PLGA Nanospheres

87%
Koneracká M., Závišová V., Timko M., Kopčanský P., Tomašovičová N., Csach K.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
595-598
EN
In this study, the biocompatible magnetic fluid was encapsulated in biodegradable polymer PLGA (poly D, L/lactide-co-glycolide acid) by the nanoprecipitation method. We characterized these spheres in terms of morphology, magnetite content and magnetic properties. The results showed good encapsulation with magnetite content 22wt% and magnetization 3.4 mT. The transmission electron microscopy and scanning electron microscopy images showed that magnetic particles have almost a spherical shape with approximate size 250 nm. Infrared spectroscopy and thermogravimetric analysis measurements were used to confirm incorporation of magnetic particles into the PLGA polymer.
16
Content available remote

Dielectric Properties of Magnetic Liquids in High Electric Fields

87%
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.
17
Content available remote

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

87%
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.
18
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Magnetic Properties of Bacterial Nanoparticles

87%
Timko M., Džarová A., Kováč J., Kopčanský P., Gojzewski H., Szlaferek A.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
381-383
EN
The objective of this study is to prepare and study magnetic properties of biological magnetic nanoparticles (magnetosomes) as a product of biomineralization process of magnetotactic bacteria Magnetospirillum sp. AMB-1. From temperature dependence of remanent magnetization and coercive field the Verwey transition is clearly seen at 105 K as a consequence of the large anisotropy along the chains of magnetosomes.
19
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Lysozyme Amyloid Fibrils Doped by Carbon Nanotubes

87%
Majorošová J., Tomašovičová N., Mitróová Z., Rajňák M., Girman V., Kopčanský P.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
588-590
EN
Production of new composites for the creation of modern materials with desired properties is the key feature of nanotechnology. Despite the well known advantages of magnetic nanoparticles, the aim of the present study was to synthesize lysozyme amyloid fibrils from hen egg white and subsequently doped this solution with single walled carbon nanotubes and with the magnetite Fe₃O₄ labelled single walled carbon nanotubes. Transmission electron microscopy and polarization optical microscopy were used to obtain the structural and dimensional information about samples. Measurements of magnetic properties indicate the considerable increase of the saturation magnetization for solutions included the magnetite nanoparticles.
20
Content available remote

Thermal Analysis of Magnetic Polymer Nanospheres for Drug Targeting

87%
Juríková A., Csach K., Miškuf J., Koneracká M., Závišová V., Kopčanský P.
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issue 5
990-992
EN
Poly(D,L-lactic-co-glycolic) acid (PLGA) polymer nanospheres loaded with different input amounts of anticancer drug taxol were prepared by the modified nanoprecipitation method. Magnetite was incorporated into the polymer nanospheres to impart them superparamagnetic properties. Thermal properties of the drug loaded magnetic polymer nanospheres were characterized using differential scanning calorimetry and thermogravimetric analysis. The solid state solubility of taxol in PLGA nanospheres and the influence of external magnetic field on their thermal stability were estimated. The investigations have revealed that the samples of dried taxol loaded magnetic PLGA nanospheres undergo mass loss at three stages during heating.
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