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1
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Influence of Mn Doping on Magnetic and Structural Properties of Co₂FeSi Heusler Alloy

100%
Galdun L., Ryba T., Kováč J., Prida V., Hernando B., 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
866-868
EN
We have studied the effect of Mn doping on structural and magnetic properties of Co₂FeSi Heusler alloy. Co₂FeSi, Co₂Mn_{0.25}Fe_{0.75}Si and Co₂Mn_{0.5}Fe_{0.5}Si alloys were prepared by melt spinning technique which offers fast and simple production of large amount of materials in a single production step. The rapid quenching method provides an opportunity to prepare Heusler alloys with highly ordered L2₁ structure confirmed by X-ray analysis in all the samples. Magnetic measurements revealed high Curie temperatures (>1000 K) and well defined easy magnetization plane parallel with the ribbon plane. Those attributes predispose given samples for applications in spintronics.
2
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Structure of Melt-Spun Co₂MnAl Heusler Alloy

100%
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.
3
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Magnetic and Structural Characterization of NiXSb (X = Mn, Cr) Heusler Ribbon

100%
Ryba T., Vargova Z., Ilkovic S., Reiffers M., Kravcak J., Gyepes R., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
857-859
EN
Half-Heusler alloys with composition NiMnSb and NiCrSb have been prepared by rapid-quenching method. NiMnSb half-Heusler alloy is characterized by single phase C1_{b} with polycrystalline structure while crystalline structure of NiCrSb shows multiphase system. Magnetic measurements indicated high anisotropy and easy magnetization direction in the parallel direction with respect to ribbon axis for NiMnSb alloy while paramagnetic behavior appears for NiCrSb alloy down to 50 K.
4
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Magnetic Characterization of Co_2MnSi Heusler Microwires

100%
Ryba T., Vargova Z., Varga R., Kováč J., Zhukova V., Zhukov A.
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vol. 126
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issue 1
196-197
EN
We report on the basic magnetic properties of glass-coated Co_2MnSi Heusler microwires. Measurements of hysteresis loops in different directions show that easy magnetization axis coincides with the wire's axis. The frequency dependence of the coercive field has been measured at room temperature in the frequency range from 10 Hz to 10 kHz. The coercivity decreases with the frequency up to 100 Hz and then increases linearly up to 1 kHz.
5
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Andreev Reflection Spectroscopy Study of Spin Polarization in Co₂Cr(Fe)Al Heusler Alloys

100%
Hašková V., Szabó P., Kováč J., Ryba T., Vargová Z., Varga R.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
377-378
EN
The present paper is dealing with the experimental study of the influence of Fe substitution on the Curie temperature and spin polarization in Co₂CrAl Heusler alloys. A recently successfully introduced new rapid quenching method has been used for the preparation of Co₂CrAl and Co₂Cr_{0.6}Fe_{0.4}Al ribbon samples. The Curie temperatures have been determined from magnetization measurements being 378 K for Co₂CrAl and much above 400 K for Co₂Cr_{0.6}Fe_{0.4}Al. The spin polarization parameter P₀ of the studied samples has been estimated from point-contact Andreev reflexion spectroscopy measurements. In pure Co₂CrAlP₀ = 0.5 - 0.9, and in the case of Co₂Cr_{0.6}Fe_{0.4}AlP₀ = 0.4 - 0.9. Hence, it is shown that Fe substitution of Cr in Co₂Cr_{1-x}FeₓAl Heusler alloys at a concentration of x=0.4 significantly increase the Curie temperature without marked influence on the spin polarization.
6
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Magnetic and Structural Characterization of Nickel and Iron Based Heusler Ribbons Ni₂FeZ (Z = In, Sn, Sb)

100%
Frol'ová L., Ryba T., Vargová Z., Komanický V., Kováč J., Gyepes R., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
735-737
EN
Comparison of structural, chemical, and magnetic properties of Ni₂FeZ (Z = In, Sn, Sb) Heusler ribbons produced by melt-spinning method is presented. The aim of work was to prepare the Heusler alloys with the appropriate chemical composition in a single step without additional thermal treatment. Scanning electron microscopy analysis revealed polycrystalline structure of all samples. It is shown that correct L2₁ structure of Ni₂FeSb can be obtained in a single production step. On the other hand, no Heusler L2₁ phase (nor its variants) occur in Ni₂FeSn alloy. Additionally, magnetic characterization revealed high Curie temperatures of the Heusler phases (above 600 K for Ni₂FeSb and 800 K for Ni₂FeIn).
7
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Structural and Magnetic Characterization of NiMnSb Half-Heusler Alloy Prepared by Rapid Quenching

84%
Ryba T., Vargova Z., Varga R., Ilkovic S., Reiffers M., Haskova V., Szabo P., Kravcak J., Gyepes R.
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vol. 126
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issue 1
206-207
EN
NiMnSb half-Heusler alloy in the form of a rod has been prepared by rapid quenching (suction-casting) method. The rod is characterized by single phase C1_b crystalline structure with lattice parameter a=5.982 Å. Magnetic measurements reveal an isotropic character of bulk NiMnSb alloy. Our study shows relatively high spin polarization of bulk NiMnSb in the range 35-50%.
8
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Ni_2FeSi Heusler Glass Coated Microwires

84%
Galdun L., Ryba T., Prida V., Hernando B., Zhukova V., Zhukov A., 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
851-853
EN
We report on fabrication, structural and magnetic properties of novel Heusler-type glass coated Ni₂FeSi microwires that were prepared by the Taylor-Ulitovsky method, having a metallic nucleus diameter about 3.9 μm and total sample diameter of 39 μm. This single step and low cost fabrication technique offers to prepare up to km of glass-coated microwires starting from few g of cheap elements for diverse applications. The X-ray diffraction data from the metallic nucleus indicates L2₁ crystalline structure (a=5.563 Å), with a possible DO3 disorder. Magnetic measurements determined the Curie temperature well above the room temperature (770 K) together with uniform easy magnetization axis of the metallic core, which predisposes this material to a suitable candidate for spintronic applications.
9
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Coexistence of Ferromagnetism and Superconductivity in Rapidly Quenched Ni_2NbSn Heusler Alloy

84%
Kanuch P., Ryba T., Gamcová J., Kanuchova M., Durisin M., Saksl K., Vargova Z., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1057-1059
EN
We present the study on production and structural, electric and magnetic properties of superconductive Ni₂NbSn Heusler alloy. The sample has been produced by melt-spinning method using tangential speed of copper wheel 20 m/s. Polycrystalline structure has been obtained showing single phase with B2 disorder with lattice constant a=6.1654 Å. Resistance measurement shows superconductive behavior with critical temperature close to 5 K. Magnetic measurements also exhibit diamagnetic contribution from superconductive phase. Additionally, the ferromagnetic state has been observed below 20 K, which points to the coexistence of magnetic and superconducting state.
10
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Novel Applications of Bistable Magnetic Microwires

69%
Sabol R., Klein P., Ryba T., Hvizdos L., Varga R., Rovnak M., Sulla I., Mudronova D., Galik J., Polacek I., Zivcak J., Hudak R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1150-1152
EN
Few examples of technical and biomedical applications of bistable magnetic microwires are shown. Particularly, application of microwires in civil engineering are shown for sensing the mechanical stress in concrete, steel structure or steel cable by simple gluing it on the surface of studied structure. On the other hand, biomedical applications for sensing the stress, temperature, and position inside the human or animal body are shown. Experiments with pig intestine cells points to the biocompatibility of glass coated microwires.
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