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1
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High-Frequency Absorbing Performances of Carbonyl Iron/MnZn Ferrite/PVC Polymer Composites

100%
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
687-689
EN
We have prepared composite materials with a mixture of carbonyl iron (CI) and manganese-zinc ferrite (MnZn) as filler and polyvinylchloride (PVC) as polymer matrix, and then electromagnetic wave absorption properties of CI/MnZn/PVC composites have been studied in the frequency range from 10 MHz to 6.5 GHz. Increasing carbonyl iron loading (to the detriment of MnZn ferrite) results in the rise of permeability and magnetic resonance loss (especially in GHz frequency range) which leads to the shift of absorption peak towards lower frequency and to the decrease of matching thickness. On the contrary, increasing MnZn ferrite loading (to the detriment of carbonyl iron) results in higher absorption bandwidth. The obtained results indicate that the prepared flexible composites may be useful as thin and/or wideband microwave absorbers.
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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Complex Permeability of LiZn/MnZn/PVC Composite Materials

81%
Dosoudil R., Ušáková M., Grusková A., Sláma J.
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issue 5
1049-1050
EN
The effect of particle content, size, and the fraction ratio of the double LiZn/MnZn ferrite filler in hybrid LiZn/MnZn/PVC composites on the frequency dispersion of complex permeability has been studied in the 1 MHz-3 GHz frequency range. The obtained relaxation type of permeability dispersion is due to the domain wall resonance, the natural ferromagnetic resonance, and the relaxation of magnetization rotation. The permeability and resonance/relaxation frequency of composites seem to be strongly affected by the change of particle content and fraction ratio of the double ferrite filler rather than by particle size.
5
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Optimization of Magnetic and Structural Properties of Sr Ferrite Prepared by Low-Temperature Combustion

81%
Grusková A., Jančárik V., Sláma J., Ušáková M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
557-560
EN
Fine strontium hexaferrite particles were prepared by the low temperature auto-combustion method. Aqueous solution of the corresponding metal salts and a combustible co-reactant compound - glycine were used as initial precursor. The resulting powders were calcined at various temperatures from 750°C up to 1100°C. The microstructure and magnetic properties were investigated by the Mössbauer spectroscopy, thermomagnetic analysis, scanning electron microscopy, and vibrating magnetometer. The particles of sizes less than 1 μm have monophasic hexagonal structure. Coercivity H_c≈400 kA/m, specific saturation polarization J_{s-m} ≈ 72×10^{-6} Tm^3 kg^{-1} and remanence polarization J_{s-r} ≈ 43×10^{-6} T m^3 kg^{-1} were achieved for the Sr ferrite annealed at 850°C for 6 h.
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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Effect of Filler Mixture Ratio on Permeability of Multicomponent Soft Magnetic Composites

81%
Dosoudil R., Ušáková M., Grusková A., Sláma J.
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vol. 126
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issue 1
404-405
EN
Composites with hybrid LiZnTi ferrite/FeSiAl alloy filler and PVC polymer matrix were synthesized by thermal pressing process. The influence of the mixture ratio of hybrid filler on the frequency dispersion of complex permeability of the composites has been studied. The dispersion of permeability varied from resonance type to relaxation one with the configuration change from LiZnTi/PVC composite to FeSiAl/PVC one and was mainly due to the magnetic resonance phenomena such as domain wall and spin precession resonance and due to the eddy current effect.
8
Content available remote

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.
9
Content available remote

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.
10
Content available remote

Frequency Variation of Complex Permeability in Dual Ferrite Filler - Single Polymeric Matrix Composites

81%
Dosoudil R., Ušáková M., Sláma J., Grusková A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
621-624
EN
The frequency dependences of complex initial permeability for triple-component composite materials based on two different types of ferrite filler (MnZn and NiZn ferrite) and a nonmagnetic polymeric matrix (PVC) were studied in the frequency range of 10 kHz-1 GHz. The frequency dispersion of permeability is discussed by means of a dynamic model based on the superposition of the two types of magnetic resonance, the resonance of vibrating domain walls and the resonance of precessing magnetic moments in domains.
11
Content available remote

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.
12
Content available remote

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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