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1
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Investigation of Two-Stage Magnetic Barkhausen Noise Measurement Method at Power Line Frequency

100%
Pal'a J., Šoka M.
Acta Physica Polonica A
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2016
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vol. 129
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issue 3
383-387
EN
The aim of the paper was to study the features of measurement of the magnetic Barkhausen noise by the new two-stage method in the high excitation frequency region (power line frequency). The magnetic Barkhausen noise was investigated on grain oriented Fe-3%Si steel subjected to different heat treatment. By application of an air coil on the output of the power amplifier we were able to linearize the excitation field. At the same time, the air coil suppressed the unwanted noise from the output of the power amplifier. We have found that the two-stage method is able to reveal a peak of the power spectrum even if it is located at low frequency, in contrast to the classical one-stage method. Further, we successfully applied a model of the power spectrum to the real magnetic Barkhausen noise obtained from the two-stage measurement.
2
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Nickel/Zinc Ratio and Lanthanum Substitution Effect on Structural and Magnetic Properties of Nickel Zinc Ferrites

81%
Jančárik V., Šoka M., Ušáková M., Harťanský R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
693-695
EN
Improvement of NiZn ferrites properties by means on Ni/Zn content ratio modification and by partial substitution of Fe³⁺ ions by La³⁺ ions is presented. Ni_{x}Zn_{1-x}Fe₂O₄ and Ni_{x}Zn_{1-x}La_{0.02}Fe_{1.98}O₄ samples of small particles were prepared by self-propagated combustion method. X-ray spectroscopy was used for structural analysis, temperature dependence of magnetic susceptibility was used for evaluation of chemical and phase composition. Analysis showed that pure spinel structure without secondary phase caused by La ions for all values of Ni/Zn content was present. Noticeable growth of the magnetic susceptibility at room temperature was observed with rising of Zn²⁺ ions content.
3
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Microstructural and Magnetic Characteristics of Divalent Zn, Cu and Co-Doped Ni Ferrites

81%
Šoka M., Dosoudil R., Ušáková M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
690-692
EN
Divalent zinc, copper and cobalt doped nickel ferrites with the chemical formula Ni_{1-x-y-z}Zn_{x}Cu_{y}Co_{z}Fe₂O₄ where x values ranging from 0.4 to 0.6, y=0.1, z=0.01 and 0.02 have been synthesized by conventional ceramic method. The effect of Zn²⁺, Cu²⁺ and Co²⁺ ions substitution on the selected microstructural and magnetic characteristics have been investigated to examine the utility of prepared ferrite materials for high-frequency applications. X-ray diffraction measurements confirmed the single-phase spinel cubic structure in all the samples and modifications in lattice parameter according to the ionic radii size of doped ions. The net magnetic moment, given by the differences between the magnetic moments of A and B sublattice, increased with raising substitution of Ni²⁺ ions. The measured frequency dispersion of complex permeability was discussed in terms of the changes in chemical composition, microstructure and the associated processes of resonance and/or relaxation due to domain wall movements and damping of spin rotations contributing to the fall of permeability and rise of magnetic losses.
4
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Magnetic Properties of Yttrium-Substituted NiZn Ferrites

81%
Jančárik V., Ušák E., Šoka M., Ušáková M.
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vol. 126
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issue 1
90-91
EN
Polycrystalline NiZn ferrite doped with a small amount of Y^{3+} ions and having the composition of Ni_{0.42}Zn_{0.58}Y_{x}Fe_{2-x}O_{4}, where x=0.00, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.10, was analyzed. Specimens were prepared by the ceramic method. Thermo-magnetic analysis and evaluation of hysteresis loops parameters were chosen as main examination methods in this study. Various parameters, such as Curie temperature T_{C}, coercive field H_{c}, remanent magnetic flux density B_{r}, hysteresis loop area and amplitude/initial permeability were studied at low frequencies.
5
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Magnetic Properties of Ni_{0.3}Zn_{0.7}Fe₂O₄ Ferrites with Iron Ions Partly Substituted by Europium

81%
Ušák E., Ušáková M., Šoka M., Vašut D.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
717-719
EN
This work is devoted to the study of the impact of the substitution of iron by Eu on the properties of magnetically soft Ni_{0.3}Zn_{0.7}Eu_{x}Fe_{2-x}O_4 ferrites aimed at enhancement of the knowledge related to the behavior of such materials in dependence on the amount of iron substitution. Our latest studies focused on the materials having similar chemical composition gave a hint of some possible approaches to manage the resulting magnetic properties in a precisely controlled way by the combination of several factors; choice of initial chemical composition of non-substituted ferrite, selection of substituted and substituting element, variations of final chemical composition, modifications of fabrication technology (sintering temperature and time), etc.
6
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Structural and Magnetic Properties of Nano-Sized NiZn Ferrites

81%
Ušák E., Šoka M., Ušáková M., Dobročka E.
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vol. 126
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issue 1
68-69
EN
Structural and magnetic properties (such as e.g. size of crystallites, lattice parameter, magnetic susceptibility, Curie temperature, etc.) of nano-sized Ni_{0.33}Zn_{0.67}Fe_{2}O_{4} ferrites have been studied. The obtained results demonstrated that the sintering temperature is an efficient and simple tool for controlling the size of crystallite particles, thus affecting the resulting magnetic properties. Straightforward relationship between the sintering temperature and the size of crystallites was found, meanwhile no other crystalline phases than the spinel one were detected by two independent analytic methods.
7
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Hopkinson Effect in Soft and Hard Magnetic Ferrites

71%
Sláma J., Ušáková M., Šoka M., Dosoudil R., Jančárik V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
762-764
EN
The dependences of the susceptibility of selected spinel and hexagonal ferrites on temperature are analyzed. The susceptibility shows a peak just below the Curie temperature T_{C} due to the Hopkinson effect during the heating. The appearance of this effect is associated with a transition from the region of stable magnetization state to superparamagnetic relaxations of the magnetic particles. It is in contrast to other explanations of the Hopkinson effect. These results are compared with measured particles size and with scanning electron microscope micrographs of both types of ferrites.
8
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Magnetic Properties of Divalent (Ni,Sn,Zn)- Tetravalent (Ru,Sn) Ionic Mixtures of Substituted Ba Ferrite

71%
Sláma J., Grusková A., González Angeles A., Šoka M., Dosoudil R.
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vol. 126
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issue 1
172-173
EN
The drop of coercivity, while preserving the saturation magnetic polarisation J_{S} of substituted M-type Ba hexaferrites with composition BaFe_{12-2x}(Me_{1}Me_{2})_{x}O_{19}, was studied. Divalent Me_{1}=Ni, Zn, Sn and tetravalent Me_{2}=Ru, Sn ionic combinations were used in various compounds. Mössbauer spectroscopy was used to reveal sites of replacement of the Fe^{3+} ions by Ru^{4+} and Sn^{4+}. The Ni^{2+}, Zn^{2+} and Sn^{2+} occupation sites were identified as well. Strong drop of coercivity difference Δ H_{c}(x) near x=0.1 and slight decrease of Δ H_{c}(x) close to x=0.3 was obtained for suitable coupling of Me_{1}^{2+ }and Me_{2}^{4+} ions.
9
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Influence of High Energy Heavy Ions on Magnetic Susceptibility of Soft Magnetic Metallic Glasses

62%
Pavlovič M., Miglierini M., Mustafin E., Seidl T., Šoka M., Ensinger W.
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vol. 126
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issue 1
54-55
EN
This contribution presents experimental data concerning the influence of fast heavy ions on magnetic susceptibility of VITROVAC®6025 and VITROPERM®800 metallic glasses. Samples of magnetic ribbons were irradiated with Au, and Ta ions at 11.1 MeV/A (energy per nucleon), and U ions at 5.9 MeV/A. The irradiation fluences varied from 5×10^{10} up to 1.2×10^{13} ions/cm^{2}. Relative change of the samples' magnetic susceptibility after and before irradiation was measured and evaluated as a function of the irradiation fluence. Measurements were done with a commercial Kappa-bridge device. We observed that VITROPERM® showed less change of magnetic susceptibility in comparison with VITROVAC® and this change occurred at higher fluences. This indicates higher radiation hardness of VITROPERM® compared with VITROVAC® against high-energy heavy ions. In addition, heavier ions caused larger change of magnetic susceptibility than the lighter ones and the effect could be roughly scaled with the level of electronic stopping.
10
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Ion Irradiation Studies of Soft Magnetic Metallic Glasses

62%
Pavlovič M., Miglierini M., Mustafin E., Seidl T., Ensinger W., Strašík I., Šoka M.
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issue 5
754-755
EN
Finemet and Vitrovac® 6025 metallic glasses were irradiated by light (N) and heavy (Au and Ta) ions at different energies from 110 keV to 250 MeV/u (MeV per mass unit) and fluences from 1 × 10^{11} ions/cm^2 to 1 × 10^{17} ions/cm^2. They were analysed by the Mössbauer spectrometry and magnetic susceptibility measurements. Qualitative differences were observed between the radiation effects caused by light and heavy ions.
11
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Study of Magnetic and Structural Properties of Non-Stoichiometric NiZn Ferrites Prepared by Wet Method

62%
Grusková A., Sláma J., Ušáková M., Šoka M., Dosoudil R., Degmová J.
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issue 5
780-781
EN
An iron-deficient (Ni_{0.33}Zn_{0.67})_{1 + x}Fe_{2 - x}O_4 and stoichiometric Ni_{0.45}Zn_{0.55}Fe_2O_4 prepared by a wet method were studied using the Mössbauer spectroscopy and thermomagnetic measurements. For the iron-deficient sample the T_{C} is twice as large and the temperature coefficient of initial permeability is two orders of magnitude lower in comparison with the stoichiometric samples. The results are supplemented by the frequency dependence of the complex permeability.
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