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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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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.
3
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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.
4
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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.
5
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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.
6
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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.
7
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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.
8
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Study of Magnetic and Structural Properties of Non-Stoichiometric NiZn Ferrites Prepared by Wet Method

61%
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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