Publications by authors named "Michal Urbánek"

14 Publications

  • Page 1 of 1

Dipolar-stabilized first and second-order antiskyrmions in ferrimagnetic multilayers.

Nat Commun 2021 May 10;12(1):2611. Epub 2021 May 10.

Institute of Physics, University of Augsburg, Augsburg, Germany.

Skyrmions and antiskyrmions are topologically protected spin structures with opposite vorticities. Particularly in coexisting phases, these two types of magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now antiskyrmions were exclusive to materials with D symmetry. In this work, we show first and second-order antiskyrmions stabilized by magnetic dipole-dipole interaction in Fe/Gd-based multilayers. We modify the magnetic properties of the multilayers by Ir insertion layers. Using Lorentz transmission electron microscopy imaging, we observe coexisting antiskyrmions, Bloch skyrmions, and type-2 bubbles and determine the range of material properties and magnetic fields where the different spin objects form and dissipate. We perform micromagnetic simulations to obtain more insight into the studied system and conclude that the reduction of saturation magnetization and uniaxial magnetic anisotropy leads to the existence of this zoo of different spin objects and that they are primarily stabilized by dipolar interaction.
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http://dx.doi.org/10.1038/s41467-021-22600-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8110839PMC
May 2021

Superparamagnetic ZnFeO Nanoparticles-Reduced Graphene Oxide-Polyurethane Resin Based Nanocomposites for Electromagnetic Interference Shielding Application.

Nanomaterials (Basel) 2021 Apr 25;11(5). Epub 2021 Apr 25.

Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno, Czech Republic.

Superparamagnetic ZnFeO spinel ferrite nanoparticles were prepared by the sonochemical synthesis method at different ultra-sonication times of 25 min (ZS25), 50 min (ZS50), and 100 min (ZS100). The structural properties of ZnFeO spinel ferrite nanoparticles were controlled via sonochemical synthesis time. The average crystallite size increases from 3.0 nm to 4.0 nm with a rise of sonication time from 25 min to 100 min. The change of physical properties of ZnFeO nanoparticles with the increase of sonication time was observed. The prepared ZnFeO nanoparticles show superparamagnetic behavior. The prepared ZnFeO nanoparticles (ZS25, ZS50, and ZS100) and reduced graphene oxide (RGO) were embedded in a polyurethane resin (PUR) matrix as a shield against electromagnetic pollution. The ultra-sonication method has been used for the preparation of nanocomposites. The total shielding effectiveness (SE) value for the prepared nanocomposites was studied at a thickness of 1 mm in the range of 8.2-12.4 GHz. The high attenuation constant (α) value of the prepared ZS100-RGO-PUR nanocomposite as compared with other samples recommended high absorption of electromagnetic waves. The existence of electric-magnetic nanofillers in the resin matrix delivered the inclusive acts of magnetic loss, dielectric loss, appropriate attenuation constant, and effective impedance matching. The synergistic effect of ZnFeO and RGO in the PUR matrix led to high interfacial polarization and, consequently, significant absorption of the electromagnetic waves. The outcomes and methods also assure an inventive and competent approach to develop lightweight and flexible polyurethane resin matrix-based nanocomposites, consisting of superparamagnetic zinc ferrite nanoparticles and reduced graphene oxide as a shield against electromagnetic pollution.
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http://dx.doi.org/10.3390/nano11051112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8145072PMC
April 2021

Spin-Wave Emission from Vortex Cores under Static Magnetic Bias Fields.

Nano Lett 2021 Feb 5;21(4):1584-1590. Epub 2021 Feb 5.

Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.

We studied the influence of a static in-plane magnetic field on the alternating-field-driven emission of nanoscale spin waves from magnetic vortex cores. Time-resolved scanning transmission X-ray microscopy was used to image spin waves in disk structures of synthetic ferrimagnets and single ferromagnetic layers. For both systems, it was found that an increasing magnetic bias field continuously displaces the wave-emitting vortex core from the center of the disk toward its edge without noticeably altering the spin-wave dispersion relation. In the case of the single-layer disk, an anisotropic lateral expansion of the core occurs at higher magnetic fields, which leads to a directional rather than radial-isotropic emission and propagation of waves. Micromagnetic simulations confirm these findings and further show that focusing effects occur in such systems, depending on the shape of the core and controlled by the static magnetic bias field.
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http://dx.doi.org/10.1021/acs.nanolett.0c03740DOI Listing
February 2021

The Photostability of Novel Boron Hydride Blue Emitters in Solution and Polystyrene Matrix.

Materials (Basel) 2021 Jan 27;14(3). Epub 2021 Jan 27.

Centre of Polymer Systems, Tomas Bata University in Zlín, třída Tomáše Bati 5678, 760 01 Zlín, Czech Republic.

In recent work, the boron hydride -BH was announced in the literature as a new laser dye, and, along with several of its derivatives, its solutions are capable of delivering blue luminescence with quantum yields of unity. However, as a dopant in solid polymer films, its luminescent efficiencies reduce dramatically. Clarification of underlying detrimental effects is crucial for any application and, thus, this contribution makes the initial steps in the use of these inorganic compounds in electrooptical devices based on organic polymer thin films. The photoluminescence behavior of the highly luminescent boron hydrides, -BH and 3,3',4,4'-Et--BH, were therefore investigated. The quantum yields of luminescence and photostabilities of both compounds were studied in different solvents and as polymer-solvent blends. The photophysical properties of both boranes are evaluated and discussed in terms of their solvent-solute interactions using photoluminescence (PL) and NMR spectroscopies. The UV degradability of prepared thin films was studied by fluorimetric measurement. The effect of the surrounding atmosphere, dopant concentration and the molecular structure were assessed.
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http://dx.doi.org/10.3390/ma14030589DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7865770PMC
January 2021

Excellent, Lightweight and Flexible Electromagnetic Interference Shielding Nanocomposites Based on Polypropylene with MnFeO Spinel Ferrite Nanoparticles and Reduced Graphene Oxide.

Nanomaterials (Basel) 2020 Dec 10;10(12). Epub 2020 Dec 10.

Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno, Czech Republic.

In this work, various tunable sized spinel ferrite MnFeO nanoparticles (namely MF20, MF40, MF60 and MF80) with reduced graphene oxide (RGO) were embedded in a polypropylene (PP) matrix. The particle size and structural feature of magnetic filler MnFeO nanoparticles were controlled by sonochemical synthesis time 20 min, 40 min, 60 min and 80 min. As a result, the electromagnetic interference shielding characteristics of developed nanocomposites MF20-RGO-PP, MF40-RGO-PP, MF60-RGO-PP and MF80-RGO-PP were also controlled by tuning of magnetic/dielectric loss. The maximum value of total shielding effectiveness (SE) was 71.3 dB for the MF80-RGO-PP nanocomposite sample with a thickness of 0.5 mm in the frequency range (8.2-12.4 GHz). This lightweight, flexible and thin nanocomposite sheet based on the appropriate size of MnFeO nanoparticles with reduced graphene oxide demonstrates a high-performance advanced nanocomposite for cutting-edge electromagnetic interference shielding application.
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http://dx.doi.org/10.3390/nano10122481DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7763453PMC
December 2020

The presence of fine and ultrafine particulate matter in the work environment.

Cent Eur J Public Health 2020 10;28 Suppl:S31-S36

Institute of Hygiene and Epidemiology, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic.

This study presents the results of pilot measurement, where the exposure of fine and ultrafine particulate matter was monitored. The measurement was performed in welding workplace, where these particles are produced unintentionally. The measurement consisted of collecting information and measuring the concentration of particles in the workplace, where data collection was focused only on inhalation exposure. During welding, primarily 300 nm size particles are produced, and their concentration is strongly influenced by the welding material, type of welding and suction. The particles are amorphous in terms of morphology and contain manganese, iron and silicon, which can cause neurodegenerative diseases. Furthermore, the results indicate the importance of monitoring oral exposure.
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http://dx.doi.org/10.21101/cejph.a6174DOI Listing
October 2020

NiFeO Nanoparticles Synthesized by Dextrin from Corn-Mediated Sol-Gel Combustion Method and Its Polypropylene Nanocomposites Engineered with Reduced Graphene Oxide for the Reduction of Electromagnetic Pollution.

ACS Omega 2019 Dec 9;4(26):22069-22081. Epub 2019 Dec 9.

Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno, Czech Republic.

In this work, nickel ferrite (NiFeO) nanoparticles were synthesized by dextrin from corn-mediated sol-gel combustion method and were annealed at 600, 800, and 1000 °C. The structural and physical characteristics of prepared nanoparticles were studied in detail. The average crystallite size was 20.6, 34.5, and 68.6 nm for NiFeO nanoparticles annealed at 600 °C ([email protected]), 800 °C ([email protected]), and 1000 °C ([email protected]), respectively. The electromagnetic interference shielding performance of prepared nanocomposites of NiFeO nanoparticles ([email protected] or [email protected] or [email protected]) in polypropylene (PP) matrix engineered with reduced graphene oxide (rGO) have been investigated; the results indicated that the prepared nanocomposites consisted of smaller-sized nickel ferrite nanoparticles exhibited excellent electromagnetic interference (EMI) shielding characteristics. The total EMI shielding effectiveness (SE) for the prepared nanocomposites have been noticed to be 45.56, 36.43, and 35.71 dB for [email protected], [email protected], and [email protected] nanocomposites, respectively, at the thickness of 2 mm in microwave X-band range (8.2-12.4 GHz). The evaluated values of specific EMI shielding effectiveness (SSE) were 38.81, 32.79, and 31.73 dB·cm/g, and the absolute EMI shielding effectiveness (SSE/t) values were 388.1, 327.9, and 317.3 dB·cm/g for [email protected], [email protected], and [email protected], respectively. The prepared lightweight and flexible sheets can be considered useful nanocomposites against electromagnetic radiation pollution.
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http://dx.doi.org/10.1021/acsomega.9b03191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6933775PMC
December 2019

Impact of sonochemical synthesis condition on the structural and physical properties of MnFeO spinel ferrite nanoparticles.

Ultrason Sonochem 2020 Mar 23;61:104839. Epub 2019 Oct 23.

Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno, Czech Republic.

Herein, we report sonochemical synthesis of MnFeO spinel ferrite nanoparticles using UZ SONOPULS HD 2070 Ultrasonic homogenizer (frequency: 20 kHz and power: 70 W). The sonication time and percentage amplitude of ultrasonic power input cause appreciable changes in the structural, cation distribution and physical properties of MnFeO nanoparticles. The average crystallite size of synthesized MnFeO nanoparticles was increased with increase of sonication time and percentage amplitude of ultrasonic power input. The occupational formula by X-ray photoelectron spectroscopy for prepared spinel ferrite nanoparticles was (MnFe)[MnFe]O and (MnFe) [MnFe]O at sonication time 20 min and 80 min, respectively. The value of the saturation magnetization was increased from 1.9 emu/g to 52.5 emu/g with increase of sonication time 20 min to 80 min at constant 50% amplitude of ultrasonic power input, whereas, it was increased from 30.2 emu/g to 59.4 emu/g with increase of the percentage amplitude of ultrasonic power input at constant sonication time 60 min. The highest value of dielectric constant (ε') was 499 at 1 kHz for nanoparticles at sonication time 20 min, whereas, ac conductivity was 368 × 10 S/cm at 1 kHz for spinel ferrite nanoparticles at sonication time 20 min. The demonstrated controllable physical characteristics over sonication time and percentage amplitude of ultrasonic power input are a key step to design spinel ferrite material of desired properties for specific application. The investigation of microwave operating frequency suggest that these prepared spinel ferrite nanoparticles are potential candidate for fabrication of devices at high frequency applications.
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http://dx.doi.org/10.1016/j.ultsonch.2019.104839DOI Listing
March 2020

Characterisation of Polyamide (PA)12 Nanocomposites with Montmorillonite (MMT) Filler Clay Used for the Incremental Forming of Sheets.

Polymers (Basel) 2019 Jul 28;11(8). Epub 2019 Jul 28.

Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Slovenia.

In this paper, the preparation and characterisation of polymer materials suitable for single point incremental forming (SPIF) technology were performed. Three different kinds of mixtures were selected: a mixture of neat polyamide 12 (PA12), a nanocomposite with PA12 matrix and 1% clay (Cloisite 93A), and a nanocomposite with PA12 matrix and 3% clay (Cloisite 93A). Materials were produced using a melt intercalation method followed by compression moulding. According to the needs of SPIF technology, morphological and mechanical properties were investigated in the obtained mixtures. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize morphological properties. It was determined that the most desired obtained exfoliated structure of clay in the polymer matrix was achieved. Static tensile testing and dynamic mechanical analysis as well as the determination of glass transition temperature and crystallinity of all analysed materials were used to obtain mechanical and thermal properties of the mixtures. The results obtained for each mixture were compared with respect to the content of clay. The content of clay (Cloisite 93A) showed a strong influence on the properties of the obtained materials. The presence of clay (Cloisite 93A) affected the increase of tensile strength and Young's modulus, while its influence on the attained elongation was not unique.
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http://dx.doi.org/10.3390/polym11081248DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723261PMC
July 2019

Polypropylene Nanocomposite Filled with Spinel Ferrite NiFeO Nanoparticles and In-Situ Thermally-Reduced Graphene Oxide for Electromagnetic Interference Shielding Application.

Nanomaterials (Basel) 2019 Apr 16;9(4). Epub 2019 Apr 16.

Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno, Czech Republic.

Herein, we presented electromagnetic interference shielding characteristics of NiFeO nanoparticles-in-situ thermally-reduced graphene oxide (RGO)-polypropylene nanocomposites with the variation of reduced graphene oxide content. The structural, morphological, magnetic, and electromagnetic parameters and mechanical characteristics of fabricated nanocomposites were investigated and studied in detail. The controllable composition of NiFeO-RGO-Polypropylene nanocomposites exhibited electromagnetic interference (EMI) shielding effectiveness (SE) with a value of 29.4 dB at a thickness of 2 mm. The enhanced EMI shielding properties of nanocomposites with the increase of RGO content could be assigned to enhanced attenuation ability, high conductivity, dipole and interfacial polarization, eddy current loss, and natural resonance. The fabricated lightweight NiFeO-RGO-Polypropylene nanocomposites have potential as a high performance electromagnetic interference shielding nanocomposite.
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http://dx.doi.org/10.3390/nano9040621DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6523113PMC
April 2019

Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques.

J Vis Exp 2018 07 2(137). Epub 2018 Jul 2.

CEITEC BUT, Brno University of Technology;

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.
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http://dx.doi.org/10.3791/57817DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6102033PMC
July 2018

Ideally Hexagonally Ordered TiO Nanotube Arrays.

ChemistryOpen 2017 08 4;6(4):480-483. Epub 2017 Jul 4.

Center of Materials and Nanotechnologies, Faculty of Chemical Technology University of Pardubice Nam. Cs. Legii 565 53002 Pardubice Czech Republic.

Ideally hexagonally ordered TiO nanotube layers were produced through the optimized anodization of Ti substrates. The Ti substrates were firstly covered with a TiN protecting layer prepared through atomic layer deposition (ALD). Pre-texturing of the TiN-protected Ti substrate on an area of 20×20 μm was carried out by focused ion beam (FIB) milling, yielding uniform nanoholes with a hexagonal arrangement throughout the TiN layer with three different interpore distances. The subsequent anodic nanotube growth using ethylene-glycol-based electrolyte followed the pre-textured nanoholes, resulting in perfectly ordered nanotube layers (resembling honeycomb porous anodic alumina) without any point defects and with a thickness of approximately 2 μm over the whole area of the pattern.
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http://dx.doi.org/10.1002/open.201700108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5542745PMC
August 2017

High-resolution fully vectorial scanning Kerr magnetometer.

Rev Sci Instrum 2016 05;87(5):053704

CEITEC BUT, Brno University of Technology, Technická 10, 616 00 Brno, Czech Republic.

We report on the development of a high-resolution scanning magnetometer, which fully exploits the vectorial nature of the magneto-optical Kerr effect. The three-dimensional nature of magnetization is at the basis of many micromagnetic phenomena and from these data, we can fully characterize magnetization processes of nanostructures in static and dynamic regimes. Our scanning Kerr magnetometer uses a high numerical aperture microscope objective where the incident light beam can be deterministically deviated from the objective symmetry axis, therefore, both in-plane (via the longitudinal Kerr effect) and out-of-plane (via the polar Kerr effect) components of the magnetization vector may be detected. These components are then separated by exploiting the symmetries of the polar and longitudinal Kerr effects. From four consecutive measurements, we are able to directly obtain the three orthogonal components of the magnetization vector with a resolution of 600 nm. Performance of the apparatus is demonstrated by a measurement of 3D magnetization vector maps showing out-of-plane domains and in-plane domain walls in an yttrium-iron-garnet film and on a study of magnetization reversal in a 4-μm-wide magnetic disk.
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http://dx.doi.org/10.1063/1.4948595DOI Listing
May 2016

Imaging reflectometry in situ.

Appl Opt 2007 Sep;46(25):6309-13

Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic.

An innovative method of in situ real-time optical monitoring of thin film deposition and etching is presented. In this technique, intensity maps of a thin film corresponding to a series of wavelengths selected by a monochromator (300-800 nm) are recorded by a CCD camera. From the maps the reflectance spectra at individual points of the sample surface can be extracted. By fitting the reflectance spectra to the theoretical ones, the maps of a thin film morphology (including optical parameters) and their temporal development during technological processes can be obtained. The method was tested by in situ observation of the growth of silicon nitride and silicon oxide thin films prepared by ion beam sputtering and by the monitoring of etching of thermally grown SiO(2) thin films.
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http://dx.doi.org/10.1364/ao.46.006309DOI Listing
September 2007