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1
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Fe₂O₃ and Gd₂O₃ Nanoparticles Embedded in Mesoporous Silica: Magnetic Properties Comparison

100%
Kapusta O., Zeleňáková A., Hrubovčák P., Girman V., Zeleňák V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
860-862
EN
Nanocomposite materials containing Fe₂O₃ and Gd₂O₃ nanoparticles with the same concentration were prepared by nanocasting method. At this procedure silica matrix serves as nanoreactor for growth of nanoparticles. Temperature and external dc field dependences of the magnetization both samples were compared. Composite containing Fe₂O₃ nanoparticles shows superparamagnetic behaviour with blocking temperature around 45 K. Otherwise, paramagnetic properties were observed for the sample with Gd₂O₃ (above 10 K). Additionally, due to free pores the silica matrix could serve as medium to increase the number of bonded water molecules. These properties together with appropriate magnetic characteristics make studied materials suitable for magnetic resonance imaging applications.
2
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Structure and Magnetic Properties οf Fe(Mn)-Si-B-Nb-Cu Alloys

100%
Michalik S., Sovak P., Bednarcik J., Kollar P., Girman V.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
399-402
EN
According to high energy X-ray diffraction measurements no significant changes were observed in a short range atomic order of amorphous ribbons Fe_{73.5-x}Mn_xCu_1Nb_3Si_{13.5}B_9 (x=1 up to 15 at.%). Thermal stability of the as-prepared alloys was investigated by differential scanning calorimetry and by in situ X-ray diffraction measurements. The two-step crystallization process was revealed, crystallization temperatures T_{x1} and T_{x2} were influenced by Mn content (thermal separation between T_{x1} and T_{x2} completely vanished for x=9). Nanocrystalline state of annealed samples was confirmed by electron transmission microscopy. The influence of Mn substitution on magnetic properties was confirmed by thermomagnetic measurements.
3
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Characterization of Carbon Nanotubes

86%
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.
4
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Effect of Annealing Time on Structure of Fe_{72.5}Cu_{1}Nb_{2}Mo_{2}Si_{15.5}B_{7} Alloy

86%
Nemcová V., Girman V., Hrabčáková V., Michalik Š., Bednarčík J., Almáši M., Sovák P.
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vol. 126
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issue 1
116-117
EN
The process of a primary crystallization of the Fe_{72.5}Cu_{1}Nb_{2}Mo_{2}Si_{15.5}B_{7} alloys was investigated by differential thermal analysis (DTA), x-ray diffraction (XRD) and transmission electron microscopy (TEM). Amorphous ribbons were isothermally annealed for 0.5, 2, 6, 30 and 150 minutes at 520 °C. Both, the XRD and TEM study showed that the level of devitrification of the sample increases with the annealing time. The above mentioned techniques confirmed the presence of the nanocrystalline grains of the Fe_{3}Si phase and enable us to study the evolution of the identified phase.
5
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The Effects of Laser Surface Hardening on Microstructural Characteristics and Wear Resistance of AISI H11 Hot Work Tool Steel

86%
Šebek M., Falat L., Kováč F., Petryshynets I., Horňak P., Girman V.
Archives of Metallurgy and Materials
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2017
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vol. 62
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issue 3
6
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Study of Local Structure of Fe_{84}B_{16} Amorphous Alloy by Electron Diffraction

86%
Hrabčáková V., Michalik Š., Borisenko K., Girman V., Nemcová V., Sovák P.
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vol. 126
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issue 1
130-131
EN
Local atomic structure in Fe_{84}B_{16} metallic glass, prepared by melt-spinning technique in He atmosphere, was studied by electron diffraction (ED) reduced density function (RDF) analysis. RDF curves were also obtained from X-ray diffraction (XRD) patterns and compared with the data from ED. Atomic reduced density functions, G(r), calculated from ED and XRD patterns showed good agreement. Atomic structure model has been fitted to the experimental ED data using Reverse Monte Carlo (RMC) simulation.
7
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Influence of Zn on Structure and Magnetic Properties of Rapid Quenched (Fe-Zn)-Cu-Nb-Si-B Alloys

86%
Kolesar V., Michalik S., Kovac J., Girman V., Sovak P., Kollar P.
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issue 5
790-791
EN
The aim of this work was to study the influence of Zn on the formation of nanostructure in Fe_{73.5 - x}Zn_xCu_1Nb_3Si_{13.5}B_9 (x = 1, 3, 5) ribbons prepared by the melt-spinning technique. X-ray diffraction measurements proved amorphous state of the sample with x = 1. The sample with x = 3 contains a small fraction of Fe_3Si phase and the sample with x = 5 is in nanocrystalline state with the average grain size of about 25 nm. The reduced radial distribution function G(r) was calculated for local structure investigation. Increasing Zn content enhances crystallization during solidification which leads to increase of magnetocrystalline anisotropy and consequently to increase of coercivity.
8
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Lysozyme Amyloid Fibrils Doped by Carbon Nanotubes

86%
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.
9
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Exchange Bias Effect in NdFeO₃ System of Nanoparticles

73%
Vavra M., Zentková M., Mihalik M., Mihalik Jr. M., Lazúrová J., Girman V., Perovic M., Kusigerski V., Roupcova P., Jaglicic Z.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
869-871
EN
We study the effect of nanometric size on the crystal structure, magnetic environment of iron and magnetization in NdFeO₃ system of nanoparticles. The average particle size of NdFeO₃ nanoparticles increases with annealing at 600°C from about 15 nm to 40 nm. The smallest particles on annealed sample have size approximately 30 nm and typically have character of single crystalline samples. All samples adopt orthorhombic crystal structure, space group Pnma with lattice parameters a =5.5817 Å, b=7.7663 Å and c =5.456 Å for as prepared sample. The presence of superparamagnetic particles was indicated by the Mössbauer measurements. The reduction of dimensionality induces a decrease of T_{N1} from 691 K to 544 K. The shift of magnetic hysteresis loop in vertical and horizontal direction was observed at low temperatures after cooling in magnetic field. We attribute such behaviour to exchange bias effect and discuss in the frame of core-shell model.
10
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Effect of the Jahn-Teller Distortion on Double Exchange Interaction in La_{0.8}K_{0.2}MnO₃ Nanoparticles

73%
Mihalik M., Zentková M., Vavra M., Mihalik Jr. M., Lazúrová J., Girman V., Konieczny P., Fitta M., Il'kovič S.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
875-877
EN
Electric resistance and effect of hydrostatic pressure on magnetic properties has been studied on the La_{0.8}K_{0.2}MnO₃ nanoparticles. Magnetic phase transition is affected by pressure only slightly, the Curie temperature T_{C} decreases with the rate of -1.02 K/GPa, on samples with orthorhombic structure where the Jahn-Teller distortion of lattice is large. On the other hand, T_{C} increases with the rate of 20.1 K/GPa on samples with rhombohedral structure, where the Jahn-Teller distortion of lattice is absent. Insulator type of electrical resistance is characteristic feature of sample with large Jahn-Teller distortion of lattice and insulator-metal transition was observed on samples where the Jahn-Teller distortion is negligible. Our results are in line with theoretical calculation predicting that double exchange interaction is suppressed by the Jahn-Teller distortion.
11
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The Correlation between Magnetic and Structural Properties in Ni-Ti-Zr Metallic Glass

73%
Lisnichuk M., Katuna Y., Saksl K., Girman V., Gamcová J., Balga D., Ďurišin M., Kováč J., Kollár P., Sovák P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
741-743
EN
The Ni-Ti-Zr metallic glasses are due to their known shape memory properties promising alloys e.g. for micromechanical applications. In this paper structure and structure stability of one particular alloy Ni₆₀Ti₂₅Zr₁₅ at.% were examined by means of X-ray diffraction and transmission electron microscopy while magnetic properties were ascertained by vibrating-sample magnetometer with maximal applied field of 100 kA/m in the temperature range of 300-1073 K.
12
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The Structural Characterization of Ni-Ti-Zr Metallic Glass

73%
Katuna Y., Lisnichuk M., Saksl K., Girman V., Gamcová J., Balga D., Ďurišin M., Kováč J., Sovák P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
750-752
EN
Metallic glasses, in contrast to its crystalline counterparts, exhibit unique mechanical and structural properties, which make them attractive for practical applications. Especially Ni-Ti-Zr metallic glass is a promising alloy for micromechanical systems because of its known shape memory properties. Shape memory effect is connected with structural phase transformation. In this paper, the ambient-temperature-structure of Ni-Ti-Zr metallic glass is investigated using transmission electron microscopy and synchrotron X-ray diffraction, the surface and chemical analysis is documented using scanning electron microscopy. Thermal stability of the alloy has been determined using differential scanning calorimetry.
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