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1
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The Role of Temperature on the Magnetization Process in CoFeZrB/FeCuNbMoSiB Hybrid Ferromagnets

100%
Dobák S., Füzer J., Kollár P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
696-698
EN
The study presents magnetization process behaviour versus operating temperature up to 100°C in dual-phase ferromagnets in the light of their complex permeability spectra and energy losses from quasi-dc regime up to about 1 MHz upon defined peak induction. The samples consist of two Co- and Fe-based ball-milled-ribbon powders mixed in the same mass ratio. The magnetic characterization has been carried out by a digital hysteresisgraph-wattmeter using complex permeability approach to the linear material. Temperature invoked reduction of anisotropy leads to the decrease of hysteresis losses and significantly affects the low-frequency part of permeability and losses that is ascribed to domain wall movement. The high-frequency behaviour remains unchanged with respect to increase of temperature.
2
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DC Magnetic Properties of Amorphous Vitrovac Ribbon

100%
Kollár P., Birčáková Z., Füzer J., Kuźmiński M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
675-677
EN
Soft magnetic amorphous Co-based materials prepared by rapid quenching method in the form of thin ribbon are well-known due to their excellent soft magnetic properties as high permeability, low coercivity, and low magnetic losses in kHz range. The amorphous Co-Fe-B-Si material Vitrovac® 6155 U55 produced by Vacuumschmelze GmbH & Co. KG belongs to this class of materials and was investigated in as-delivered state. The aim of this work was to study DC magnetization process by various experimental methods. We have measured magnetization curve by fluxmeter based hysteresis graph and hysteresis loops by three different fluxmeter based hysteresis graphs, exhibiting significant differences. The first and the second hysteresis graph perform the hysteresis loops measurement by the point-by-point method, either with commutative or with summing steps. The third one is AC hysteresis graph working at very low frequencies down to 7 mHz, performing the continuous method. The explanation of this result is based on the structural after effect influencing the domain wall displacement. We assumed that the domain structure consists of very small number of domain walls responsible for magnetization process, which was confirmed by the visualization of static domain structure by a computer-controlled setup based on the Kerr effect.
3
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AC Magnetic Field Effect on the Complex Permeability Spectra of Soft Magnetic Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7} Powder Cores

100%
Füzer J., Dobák S., Füzerová J.
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vol. 126
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issue 1
88-89
EN
In this work, two soft magnetic Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7} powder core samples were investigated. Samples were prepared by milling of amorphous Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7} ribbon at different temperature conditions: sample R, by milling at room temperature and sample L, by cryomilling at temperature of liquid nitrogen. Influence of applied exciting AC magnetic field with various amplitudes on the complex permeability spectra was studied. Obtained results are explained by the dynamics and relaxation phenomenon of domain walls under the influence of AC magnetic field.
4
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Low Frequency Core Losses Components of FeNiMo Powder Compacted Materials

100%
Olekšáková D., Kollár P., Füzer J.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
639-641
EN
The relations of core losses with the frequency of FeNiMo alloys were investigated. The core energy losses were determined by the measurements of dc and ac hysteresis loops as functions of frequency (1 Hz-50 Hz). The usual three-component concept of separation of core losses consisting of hysteresis, eddy current and anomalous losses was used to explain the influence of the powder particle size on core loss frequency dependences.
5
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Preparation and Characterization of Fe/SiO_{2} Powder Composites Using Impregnation Method

88%
Kabátová M., Füzer J., Füzerová J., Dudrová E., Kollár P.
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vol. 126
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issue 1
134-135
EN
Fe/SiO_{2} powder composite materials based on irregularly and/or spherically shaped iron powder particles with an addition of SiO_{2} nanopowder were prepared in two ways, (i) by mixing the Fe/SiO_{2} powder with 1.0 wt.% of Shellac dissolved in ethanol and (ii) by vacuum/pressure impregnation of low-temperature sintered Fe/SiO_{2} components with shellac dissolved in ethanol and with thermoplast SL450. SiO_{2} was implemented either as nanopowder or by sol-gel coating. Vacuum/pressure impregnation (VPI) of pre-sintered samples was performed in a steel container. The influence of iron particle shape and processing conditions on the electro-insulating layer was microscopically evaluated and correlated with the values of the electrical resistivity and coercivity. It has been found that the continuity, distribution and thickness of insulating phase is strongly controlled by the shape of iron particles. Using the VPI procedure, the irregular surface of iron particles may cause discontinuities of insulating layer, while the spherical iron particles are well covered with continuous evenly distributed insulating layer.
6
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Isobaric Thermal Expansion and Isothermal Compression of Powdered NiFe Based Alloys Studied by In-Situ EDXRD

88%
Olekšáková D., Füzer J., Kollár P., Bednarčík J., Lathe C.
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vol. 126
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issue 1
128-129
EN
The aim of the present work was to study the isothermal compression and isobaric thermal expansion behaviour of ball-milled NiFe (81 wt.% of Ni) and NiFeMo (79 wt.% of Ni, 16 wt.% of Fe) alloy and follow its phase evolution when exposed to high pressure and temperature. In-situ pressure-temperature energy dispersive X-ray (EDXRD) diffraction experiments were performed at the MAX80 instrument (beamline F2.1). The compressibility of NiFe alloy at 400 °C was evaluated for pressure values of up to 3.5 GPa. The EDXRD spectra revealed the presence of cubic FeNi_{3} phase as determined from the shift of (111), (200) and (220) reflection lines in corresponding EDXRD spectra.
7
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Magnetic Properties of Crystalline NiFe Alloy Prepared by High-Energy Ball Milling and Compacting

88%
Olekšáková D., Kollár P., Füzer J., Bednarčík J., Roth S.
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issue 5
797-799
EN
The structure and magnetic properties of compacted microcrystalline NiFe (81 wt% of Ni) powder is investigated. The powder of NiFe alloy prepared by ball milling of ribbon (prepared by melt spinning) remains single phase material suitable for compaction in order to prepare soft magnetic material. The bulk samples were consolidated by uniaxial compaction of the powder in vacuum. By measuring of AC and DC magnetic properties it was found out that in bulk samples the displacement of domain walls is the dominant magnetization process, while rotation of magnetization vectors prevails in powder material.
8
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AC Magnetic Properties of Vitroperm Based Composite Materials

88%
Kollár P., Hegedüs L., Füzer J., Bureš R., Fáberová M.
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issue 5
787-789
EN
The aim of this work was to investigate the influence of resin content on AC magnetic properties of Vitroperm 800-based composite material to extend possibilities for application of this kind of material at higher frequency (up to 100 kHz). The samples of composite material were prepared in the form of the ring with outer diameter of 25 mm, inner diameter of 18 mm and height approximately 3 mm. Powder mixtures were prepared from Vitroperm 800 in partial nanocrystalline state and commercial termoset resins by mechanical mixing. The AC magnetic properties (losses) at maximum induction up to 0.5 T were measured by MATS-2010SA loop tracer in frequency range 1-100 kHz. The specific resistivity of the material was measured by the van der Pauw method. The magnetic properties of the composite rings were compared with the properties of the material prepared from Fe based powder supported by Höganäs. It was found out that the total losses of the Vitroperm-based soft magnetic composite are more than 10 times lower (at 10 kHz) than that for Fe-based one.
9
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Content available

Advances in Powder Metallurgy Soft Magnetic Composite Materials

88%
Bureš R., Strečková M., Fáberová M., Kollár P., Füzer J.
Archives of Metallurgy and Materials
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2017
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vol. 62
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issue 2
10
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The Influence of Preparation Methods on Magnetic Properties of Fe/SiO₂ Soft Magnetic Composites

88%
Füzerová J., Füzer J., Kollár P., Kabátová M., Dudrová E.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
816-818
EN
An analysis of several variants of the Fe/polymer/SiO₂ composites in terms of the impact of iron powder particle shape (irregular, spherical), of the content (0.4-2.0 wt%), of the polymer type (shellac, thermoset SL450) and the method of its application as well as the effect of the preparation procedure of the composites (mixing and/or vacuum-pressure impregnation) on properties of electrical insulating layer (thickness and coherence), electrical resistivity and magnetic properties was carried out. It was found that the main governing factor of the microstructure formation is the shape, surface microgeometry of the iron particles and the insulator layer. These determine not only the uniformity of thickness and cohesion of the insulating layer of the applied polymer or its hybrid modification (polymer+SiO₂ nanoparticles), but also the most suitable method of preparation in terms of the achieved values of electrical and magnetic properties of the composites.
11
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Influence of Film Thickness on the Microstructure and Magnetic Properties of Finemetic Thin Films

88%
Dlugoš R., Sovák P., Balcerski J., Füzer J., Kollár P.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
447-450
EN
The aim of this work was to study the influence of film thickness on the structure and magnetic properties of finemetic thin films after annealing. Thin films with the various thickness (from 20 nm up to 700 nm) were prepared by DC sputtering method. The heat treatments of the films for further structural and magnetic observations were performed at the temperature range 300-500°C for 15 min in vacuum furnace. Structural observations were carried out by transmission electron microscopy. Coercivity was determined from hysteresis loops traced with fluxmeter and Kerr magnetooptical hysteresisgraph. All the experimental results confirm a different magnetic behaviour of the thin films according to their thickness.
12
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Investigation of Total Losses of Non-Oriented Electrical Steels

76%
Füzer J., Birčáková Z., Zeleňáková A., Hrubovčák P., Kollár P., Predmerský M., Huňady J.
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issue 5
1018-1019
EN
The aim of this work was to investigate the influence of microstructural features on the soft magnetic properties. The materials chosen for this work were two types of the Epstein strips of commercially produced non-oriented electrical steels by U.S. Steel Košice. The AC magnetic properties in 0.2-100 Hz frequency range were obtained by measurements of AC hysteresis loops by a fluxmeter based non-standard single sheet AC hysteresisgraph. The influence of the grain size and magnetic domains structure on the partial contributions (hysteresis, eddy current and anomalous) to the total losses is also discussed. The results of the frequency dependence of the total losses, measured by a single sheet loop tracer along the rolling direction and perpendicular to the rolling direction, show different contribution of partial components.
13
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Microwave Sintered Fe/MgO Soft Magnetic Composite

76%
Bureš R., Fáberová M., Kollár P., Füzer J., Dobák S., Onderko F., Kurek P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
780-782
EN
Micro/nano soft magnetic composite based on the Fe microparticles and the MgO nanoparticles was prepared by cold pressing followed by microwave sintering. Magnetic and mechanical properties of the green compact as well as sintered samples were measured. Coercivity, permeability, resistivity, elastic modulus and transverse rupture strength values in dependence on MgO content were investigated. The influence of MgO content ratio on properties was different in the case of as pressed green samples in comparison to sintered bodies. Microstructure formation and its influence on mechanical and magnetic properties are discussed. The coercivity of the green compacts with 1-5 wt% of MgO exhibits approximately 460 A/m and after sintering decreases to approximately 290 A/m. The real part of complex permeability at the frequency of 100 kHz exhibits a maximum for 2 wt% of MgO in green compacts, while for 10 wt% in sintered samples. It was observed that increase of the content of MgO causes decrease of the permeability. Properties of the sintered composite are related to formation of magnesium ferrite as well as volume distribution of residual MgO in dependence on initial MgO ratio.
14
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FeSiBAlNiMo High Entropy Alloy Prepared by Mechanical Alloying

76%
Bureš R., Hadraba H., Fáberová M., Kollár P., Füzer J., Roupcová P., Strečková M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
771-773
EN
High-entropy alloys have attracted increasing attentions because of their unique compositions, microstructures, and adjustable mechanical and functional properties. In this work, mechanical and magnetic properties of the FeSiBAlNiMo high-entropy alloy were studied in heat-treated conditions. Influence of temperature and time of sintering was investigated. The lowest coercivity H_c=370 A/m was reached at sintering temperature 580°C, during 20 min in Ar/10H₂ atmosphere. Resistivity decreases from R=0.006 Ωcm at 580°C of sintering temperature to R=0.0004 Ωcm at temperature 1100°C. Transverse rupture strength TRS = 340 MPa as well as the Young modulus E=87 GPa were much higher in the case of sintering at 1100°C in comparison to TRS = 5 MPa and E=7.5 GPa at sintering temperature 580°C. Low temperature consolidation made possible to structure recovery and stress relief of amorphous-nanocrystalline structure. Higher temperature above 1100°C induced sintering processes and formation of complex borides.
15
Content available remote

Influence of Vitrovac Content on Magnetic Properties in Composite Materials Based on the Mixture of Two Ferromagnets

76%
Hegedűs L., Kollár P., Füzer J., Bureš R., Fáberová M., Kurek P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
765-767
EN
Soft magnetic composite materials play an important role in nowadays industry, replacing the traditional materials such as electrical steels and soft ferrites, especially at medium and higher frequency applications. The material can be tailored for a specific application by changing the composition of the material and by adaptation of the fabrication process. The aim of this work was to investigate the morphology, phase composition and magnetic properties of soft magnetic composite materials with various magnetic content to minimize the total magnetic losses. The prepared sample series was based on the mixture of two different ferromagnets Vitrovac 6155 and Somaloy 700 without addition of insulating material. The samples were prepared by conventional powder metallurgy with particular fraction of Vitrovac in the form of a ring for magnetic measurements in AC fields and electric resistivity measurements. The samples with 5 wt% and 20 wt% fractions of Vitrovac exhibit lower values of total losses in comparison with Somaloy heat treated at 530°C.
16
Content available remote

Investigation of Magnetization Processes from the Energy Losses in Soft Magnetic Composite Materials

76%
Birčáková Z., Kollár P., Weidenfeller B., Füzer J., Fáberová M., Bureš R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
684-686
EN
Soft magnetic composite materials are composed of small ferromagnetic particles insulated from each other. It gives them some very good properties e.g. the magnetic isotropy and low total energy losses at medium to higher frequencies. On the other hand, their structure gives rise to the negative aspects as the inner demagnetizing fields, resulting in some specifics in magnetization processes leading to the worsening of soft magnetic properties, particularly the excess losses increase and a lowering of permeability. The frequency dependence of excess losses, the low and high induction loss components and the inner demagnetization factors of soft magnetic composites were investigated in order to reveal the proportions of the reversible and irreversible magnetization processes. Higher excess losses were observed in samples with smaller particles or higher non-ferromagnetic content (resin+pores), in which the inner demagnetizing fields were higher. It was explained by lower effective number of movable domain walls in those samples, thus less irreversible magnetization processes. This was confirmed by low and high induction loss analysis, where total losses were divided into low and high induction loss components and plotted vs. frequency.
17
Content available remote

Wide Frequency Range AC Magnetic Properties of Fe-Based Composite Materials

76%
Kollár P., Birčáková Z., Füzer J., Füzerová J., Bureš R., Fáberová M.
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issue 5
759-761
EN
The aim of this work was to analyze the influence of resin content on contribution of the hysteresis, eddy current and anomalous losses to the total losses in the frequency range from DC to 150 kHz. The samples of composite material were prepared in the form of the ring with outer diameter of 25 mm, inner diameter of 17 mm and height approximately 3 mm and in the form of cylinder with diameter of 25 mm and height approximately 3 mm by a compaction of mixture of iron powder ASC100.29 (90 vol.%) and commercial termoset resins. The DC hysteresis losses were obtained by the measurements of DC hysteresis loops and the total power losses in the frequency range 0.4 Hz-150 kHz from AC hysteresis loops, both at maximum induction 0.05, 0.1 and 0.2 T. The magnetic properties of the composite rings were compared with the properties of the material prepared from the powder supported by Höganäs AB Sweden. By analyzing the frequency dependence of total losses of the Fe-based SMC we found out that hysteresis losses contribute to the total losses as a majority component.
18
Content available remote

Magnetic Properties of Soft Magnetic FeSi Composite Powder Cores

76%
Lauda M., Füzer J., Füzerová J., Kollár P., Strečková M., Fáberová M.
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vol. 126
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issue 1
144-145
EN
Soft magnetic composites (SMCs), which are used in electromagnetic applications, can be described as ferromagnetic powder particles surrounded by an electrical insulating film. These composite materials offer several advantages over traditional laminated steel cores such as reduction in weight and size. They have some unique properties, including three-dimensional isotropic ferromagnetic behaviour, very low eddy current loss, relatively low total core loss at medium and high frequencies, high electrical resistivity and good relative magnetic permeability. FeSi powder was used as a base ferromagnetic material for preparation of soft magnetic composites. The commercial FeSi particles of a precise spherical shape were prepared in two granulometric fractions (up to 150 μm or up to 356 μm). The phenol-formaldehyde resin modified by SiO_{2} nanoparticles was used as an electroinsulating layer. The FeSi particles covered by the synthesized resin were compacted at 800 MPa into the ring samples for magnetic measurements. The final samples were treated thermally under the curing schedule, which was suggested according to thermal degradation of the modified resin.
19
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Structure and Properties of Composites Based on Mixed Morphology of Ferromagnetic Particles

76%
Bureš R., Fáberová M., Strečková M., Birčáková Z., Kollár P., Füzer J.
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vol. 126
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issue 1
140-141
EN
Application potential of the soft magnetic composites increases with improvement of their functional properties. In addition to the magnetic properties, the mechanical properties of these materials are essential. The aim of this work was to investigate mechanical properties and their dependence on morphology of the ferromagnetic particles. Model composite based on Somaloy® and Vitroperm® powder was prepared using conventional powder metallurgy. The DC magnetic properties of composites based on two types of ferromagnetic particles with different shapes and structures are discussed in the relation with mechanical properties.
20
Content available remote

Mössbauer and Magnetic Study of Fe+Vitroperm+Plastic System

64%
Brzózka K., Kollár P., Szumiata T., Sovak P., Füzer J., Fáberová M., Bureš R., Górka B., Gawroński M., Gzik-Szumiata M.
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vol. 126
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issue 1
148-149
EN
Phase composition and magnetization curves of the soft magnetic composites, fabricated by compaction of several kinds of powders mixed in various proportions, have been investigated by means of conversion electron Mössbauer spectroscopy and an alternating gradient force magnetometry. The results point to significant quantity of iron oxides - hematite and magnetite - at the surface of the samples. After the rubbing of thin surface layer, the relative content of oxides was distinctly reduced. Magnetic measurements revealed very similar characteristics of hysteresis curves for all the investigated materials.
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