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1
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The Doped YBCO Superconductor Crystal Structure Simulation

100%
Kavečanský V., Diko P.
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issue 5
1034-1035
EN
Pinning process plays an important role in improving utility properties of YBa_2Cu_3O_{7-δ} (YBCO) superconductors. As a consequence of the low coherent length, the most effective pinning centers in such type of materials should have nanometer size dimensions. An efficient way of introducing such centers can be a chemical substitution in the YBCO lattice. Computer simulation of locally distorted YBCO crystal structure due to the substitutions has been performed.
2
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Magnetic Study of the Fe Coated by Au Nanoparticles

81%
Zeleňáková A., Kováč J., Kavečanský V., Zeleňák V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
533-536
EN
Nanosized iron-gold magnetic nanoparticles with an average particle size 10 nm were prepared by a reverse micelle method. The magnetic properties measurements of DC and AC magnetization confirm behaviour typical of a superparamagnetic system, such as the irreversibility of the zero-field-cooled and field-cooled curves, the frequency dependence of a blocking temperature T_B, and revealing of coercivity H_C below blocking temperature. The quantitative analysis of AC susceptibility due to value of parameter C_1 = ΔT_B/(T_B Δ log f)=0.0242 confirming the existence of inter-particle interaction in our system.
3
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Synthesis of Nanocrystalline BaCeO₃ by Oxalate Coprecipitation for YBa₂Cu₃O₇ Bulk Superconductors

81%
Verbová R., Kavečanský V., Diko P., Antal V.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
82-85
EN
Barium cerate (BaCeO₃) is one of the preferred additions to bulk YBa₂Cu₃O₇ single-grain superconductors to inhibit the growth of Y₂BaCuO₅ particles. The present paper investigates synthesis of very fine barium cerate powder and its use in YBa₂Cu₃O₇ bulk superconductor growth. The crystalline barium cerate was synthesized by oxalate co-precipitation from barium and cerium nitrates. X-ray diffraction in air and vacuum was performed to understand the formation of barium cerate as well as to determinate its crystal structure. Size and shape of BaCeO₃ particles were studied by scanning electron microscopy. The BaCeO₃ was used to grow YBa₂Cu₃O₇ bulk superconductor. Microstructure of prepared YBa₂Cu₃O₇ crystal shows that the barium cerate in the final product is very fine and uniformly distributed throughout the whole YBa₂Cu₃O₇ crystal.
4
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Electrical Resistance Anomalies in Holmium Thin Films below 20 K in Magnetic Field

71%
Dudáš J., Gabáni S., Kavečanský V., Gościańska I., Bagi J.
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issue 5
843-845
EN
Electrical resistance (R) of Ho thin films evaporated in vacuum ≈ 10^{-7} Pa was studied in a temperature range from 2 K up to 300 K and in magnetic field up to 9 T. Measurements showed resistance anomalies below 20 K - minima of R value in 36 nm and 215 nm thin films and resistivity maximum at 3.58 K in 215 nm Ho film. Increasing value of the magnetic field, applied perpendicular to film surface up to 5 T, caused increasing suppression of the R minima in these films with subsequent disappearance of them in fields above 5 T. Maximum of R value in 215 nm thin film at 3.58 K decreased with increasing flux density up to 5 T and it was suppressed at fields above 5 T. X-ray diffraction of these films revealed two phases composition consisting of the hexagonal Ho and of cubic HoH_2. The preferential crystal orientation of both phases was detected.
5
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Magnetic Properties of Thorium Ferricyanide

71%
Göbl R., Zentková M., Kavečanský V., Kováč J., Zentko A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
835-838
EN
The magnetic properties of Th_{3}[Fe(CN)_{6}]·10H_{2}O were investigated. It was shown that this compound is antiferromagnetically ordered in the low temperature region. The observed antiferromagnetic ordering is stable only in the low field.
6
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Magnetic and Transport Properties of La_{0.67}Pb_{0.33}(Mn_{1-x}Co_x)O_3

61%
Mihalik M., Kavečanský V., Maťaš S., Zentková M., Ammer J., Kellner K., Gritzner G.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
251-254
EN
Detailed studies of temperature dependences of magnetization, AC susceptibility and electrical resistance were performed on La_{0.67}Pb_{0.33}(Mn_{1-x}Co_x)O_3 ceramics with x = 0.01 and 0.1. Typical features of both compounds are the hysteretic behavior between the zero-field-cooled magnetization regime and the field-cooled magnetization regime, a very weak field dependence of a maximum in zero-field-cooled magnetization and practically no frequency dependence of the peak in AC susceptibility χ"(T). Anomalies in the electrical resistance connected with the ferromagnetic transition at T_C, the insulator-metal transitions at T_p and the re-entrant metal-isolator transition at T* are field dependent pointing to magnetic origin of these transitions. Colossal magnetoresistance was observed in both compounds.
7
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Structure of Melt-Spun Co₂MnAl Heusler Alloy

61%
Piovarči S., Diko P., Kavečanský V., Ryba T., Vargová Z., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
881-883
EN
The growth-related microstructure and texture of the Co₂MnAl-type Heusler alloy in the form of a melt-spun ribbon was studied by electron microscopy, electron backscattered diffraction and X-ray diffraction. It is shown that melt spinning produces a single-phase disordered Heusler alloy. The fine grain structure at the wheel side of the ribbon exhibits no texture, while dominant columnar grain structure formed on the free surface side exhibits the ⟨111⟩ fibre texture with a declination by about 10 degrees in the spinning direction. The dendritic growth of columnar crystals causes inhomogeneity of the chemical composition on a micrometre scale with a higher Co and Al concentration in the centre of dendritic arms and a higher concentration of Mn at the dendrite arm boundaries.
8
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Influence of Thickness and Magnetic Field on Magnetic Ordering Temperatures in Holmium Thin Films

61%
Dudáv J., Guzan M., Gabáni S., Kavečanský V., Gošciańska I., Vincze A., Konč M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
191-195
EN
Influence of thickness and magnetic field on magnetic ordering temperatures is reported. The X-ray diffraction of Ho films confirmed their preferential crystal orientation and revealed diffraction peaks originating from the hcp structure of Ho and those from inessential holmium dihydride content. Secondary ion mass spectroscopy showed a very homogeneous distribution of holmium in thin films. Electrical resistance measurements on Ho films in the thickness range from 98 nm to 215 nm showed a "knee-like" resistance anomaly near the T_N. The T_N value of these films decreased with decreasing film thickness. Magnetic field applied parallel to the thin film plane caused an increasing suppression of the T_N value up to 5 K with increasing flux density value up to 5 T.
9
Content available remote

Characterization of New U-Ni-X₂ Splats and Study of their Physical Properties

52%
Molčanová Z., Mihalik M., Mihalik M., Reiffers M., Džubinská A., Huráková M., Kavečanský V., Paukov M., Havela L.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
994-996
EN
We explored the crystal structure, magnetic, and transport properties of UNiX₂ (X = Ge, Si) materials, which were prepared by a conventional metallurgical technique and by rapid solidification - splat cooling. The UNiSi₂ splat is mostly single phase, containing only small traces of a minority phase. Magnetic and electrical properties of the splat resemble properties of samples, which were prepared by conventional methods, exhibiting a ferromagnetic transition at about 91 K and similar temperature dependence of resistivity. The coercive field of μ₀H_c=4.25 T is much enhanced due to the magnetic anisotropy introduced by the sample preparation technique. The Barkhausen jumps were observed on the hysteresis loop. Magnetization of the sample does not saturate in fields up to μ₀H=9 T. The phase structure of UNiGe₂ splat is not completely solved and will be subject of our study in future. Our preliminary results indicate the presence of completely new phase with tetragonal crystal structure and antiferromagnetic ordering below 54 K.
10
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Magnetic Relaxation and Memory Effect in Nickel-Chromium Cyanide Nanoparticles

52%
Zentko A., Kavečanský V., Mihalik M., Maťaš S., Mitróová Z., Zentková M., Maryško M., Jagličić Z.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
511-514
EN
The low temperature dynamics of a magnetic nanoparticle system Ni_3[Cr(CN)_6]_2 with an average nanoparticles size of 4 nm was studied. Using different temperature and field protocols memory phenomena were studied by the DC magnetization and magnetic relaxation measurements of the system at temperatures below T_m = 19 K. Aging experiments show an absence of any waiting time dependence in the magnetization relaxation due to a field change after zero field and field cooling. This observation discriminates the dynamics of the system from the behaviour of a classical spin-glass.
11
Content available remote

Effect of Pressure on Magnetic Properties of TM_3[Cr(CN)_6]_2 · nH_2O Nanoparticles

52%
Zentko A., Zentková M., Kavečanský V., Mihalik M., Mitróová Z., Arnold Z., Kamarád J., Cieslar M., Zeleňák V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
489-493
EN
Effect of pressure on magnetic properties of magnetic nanoparticles, based on Prussian blue analogues, were studied in pressures up to 1.2 GPa. The Mn_3[Cr(CN)_6]_2·nH_2O and Ni_3[Cr(CN)_6]_2·nH_2O nanoparticles were prepared by reverse micelle technique. Transmission electron microscopy images show nanoparticles with average diameter of about 3.5 nm embedded in an organic matrix. The characteristic X-ray peaks of nanoparticles are more diffused and broader. Systems of nanoparticles behave as systems of interacting magnetic particles. The Curie temperature T_C is reduced from T_C = 56 K for Ni-Prussian blue analogues to T_C = 21 K for Ni-nanoparticles system and from T_C = 65 K for Mn-Prussian blue analogues to T_C = 38 K for Mn-nanoparticles system. One can explain this reduction of the Curie temperature and of the saturated magnetizationμ_s by dispersion of nanoparticles in an organic matrix i.e. by a dilution effect. Applied pressure leads to a remarkable increase in T_C for system of Mn-nanoparticles (ΔT_C/Δp = +13 K/GPa) and to only slight decrease in T_C for system of Ni-nanoparticles (ΔT_C/Δp = -3 K/GPa). The pressure effect follows behavior of the mother Prussian blue analogues under pressure. The increase in saturated magnetization, attributed to compression of the organic matrix, is very small.
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