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Development of process parameters of Selective laser melting technology for the production of thin-walled iron parts
Šreibr, Vít ; Dočekalová, Kateřina (referee) ; Paloušek, David (advisor)
The thesis deals with the processing of pure iron by Selective laser melting technology as a material with good electromagnetic properties. The main area is the optimization of the production of thin-walled samples, which monitor the influence of process parameters on the thickness and quality of the wall surfaces. In addition to the perpendicular walls, walls built at an angle of 45° are also examined. Another phase of the thesis is the determination of process parameters for bulk bodies to achieve the lowest porosity and high surface quality. An important part of the research is the application of acquired knowledge in the production of samples designed to test magnetic properties as well as part for a specific application. These considerations concern not only the setting of the printing parameters, but also the heat treatment and its influence on the magnetic and mechanical properties of the material. Mechanical properties were determined by tensile tests and hardness tests. All samples were made on a SLM 280HL using a 400W ytterbium laser.
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Theoretical Investigation of Low-dimensional Magnetic Materials
Li, Shuo ; Grajciar, Lukáš (advisor) ; Frauenheim, Thomas (referee) ; Jelínek, Pavel (referee)
Low-dimensional (D) materials, such as graphene, transition metal dichalcogenides and chalcogenide nanowires, are attractive for spintronics and valleytronics due to their unique physical and chemical properties resulting from low dimensionality. Emerging concepts of spintronics devices will greatly benefit from using 1D and 2D materials, which opens up new ways to manipulate spin. A majority of 1D and 2D materials is non-magnetic, thus their applications in spintronics are limited. The exploration, design and synthesis of new 1D and 2D materials with intrinsic magnetism and high spin-polarization remains a challenge. In addition, the valley polarization and spin-valley coupling properties of 2D materials have attracted great attention for valleytronics, which not only manipulates the extra degree of freedom of electrons in the momentum space of crystals but also proposes a new way to store the information. The computational investigation of magnetic and electronic properties of low-dimensional materials is the subject of this thesis. We have systematically investigated geometric, electronic, magnetic and valleytronic properties of several 2D and 1D materials by using the density functional theory. These investigations not only theoretically show rich and adjustable magnetic properties of...
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Development of process parameters of Selective laser melting technology for the production of thin-walled iron parts
Šreibr, Vít ; Dočekalová, Kateřina (referee) ; Paloušek, David (advisor)
The thesis deals with the processing of pure iron by Selective laser melting technology as a material with good electromagnetic properties. The main area is the optimization of the production of thin-walled samples, which monitor the influence of process parameters on the thickness and quality of the wall surfaces. In addition to the perpendicular walls, walls built at an angle of 45° are also examined. Another phase of the thesis is the determination of process parameters for bulk bodies to achieve the lowest porosity and high surface quality. An important part of the research is the application of acquired knowledge in the production of samples designed to test magnetic properties as well as part for a specific application. These considerations concern not only the setting of the printing parameters, but also the heat treatment and its influence on the magnetic and mechanical properties of the material. Mechanical properties were determined by tensile tests and hardness tests. All samples were made on a SLM 280HL using a 400W ytterbium laser.
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Preparation of magnetic nanostructures of chromites and their characterization
Zákutná, Dominika ; Nižňanský, Daniel (advisor) ; Honecker, Dirk Olaf (referee)
The present Diploma thesis provides an original synthesis for the preparation magnetic cobalt chromite nanoparticles (CoCr2O4 NPs) well dispersed in non-polar solvents and extensive structural, morphological, phonon and magnetic characterization. Particular emphasis is on determination of the spiral magnetic structure in CoCr2O4 NPs prepared by various procedures such as hydrothermal synthesis and sol-gel method. CoCr2O4 NPs with diameters in the range of 3.0 - 4.1 nm are prepared by high temperature hydrothermal method. For the first time, the CoCr2O4 NPs are stable in non-polar solvents and they are prepared by one-step synthesis without post treatment. The structure of prepared NPs is refined by Rietveld analysis. Size of prepared NPs is determined and compared using various techniques as powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Magnetic measurements reveal the transition from superparamagnetic (SPM) state to super spin glass - like (SSG) state. From a.c. susceptibility measurements, the spin dynamics studies and strength of inter-particles interaction are investigated. CoCr2O4 NPs with mean diameter of 26.9(1) nm are prepared by sol-gel method. The magnetization measurements reveal the transition from superparamagnetic to...
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Structure and magnetic properties of f-electron compounds and their hydrides
Mašková, Silvie ; Havela, Ladislav (advisor) ; Kamarád, Jiří (referee) ; Reiffers, Marián (referee)
Title: Structure and magnetic properties of f-electron compounds and their hydrides Author: Silvie Mašková Department: Deparment of Condensed Matter Physics Supervisor: Doc. RNDr. Ladislav Havela, CSc., Deparment of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, The Czech Republic Abstract: Magnetic properties were studied in several types of actinide- and lanthanide-based ternary compounds. We have shown indirect that anisotropy of compressibility and thermal expansion can be related to the direction of magnetic moments at U-compounds with "soft" directions (where the closest U-U links are) perpendicular to the moments direction. Comparison of U and RE compounds of the 2-2-1 type indicates that contrary to U compounds, RE compounds can absorb much more hydrogen. The involvement of the f-states in metallic bond, which takes place at actinides and not in lanthanides, makes the U-based compounds apparently more stable against hydrogenation. Basic electronic properties were established for ζ -Pu19Os, which is a close analogy to β-Pu, and for its low-temperature variety η -Pu19Os. The results confirm that the volume is not the main parameter driving Pu properties, as β-Pu with intermediate volume is the most strongly correlated Pu phase. Keywords: uranium compounds,...
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Příprava a vlastnosti nanočástic chromitů
Zákutná, Dominika ; Nižňanský, Daniel (advisor) ; Němec, Ivan (referee)
Title: Preparation and Characterization of Chromites nanoparticles Author: Dominika Zákutná Department: Department of Inorganic Chemistry, Faculty of Science, Charles University of Prague Supervisor: RNDr. Daniel Nižňanský, Ph.D. Consultant: RNDr. Jana Vejpravová, Ph.D. Supervisor`s e-mail address: niznansk@natur.cuni.cz Abstract: This work concerns the hydrothermal preparation of cobalt chromite nanoparticles (CoCr2O4), their characterization and the study of their magnetic properties. The preparation is based on the chlorides in the water-ethanol-oleic acid system. The samples were characterized by Powder X-ray Diffraction (PXRD), Transmission and High Resolution Electron Microscopy (TEM, HRTEM), Scanning Electron Microscopy (SEM), Raman and Infrared Spectroscopy and magnetic measurements of magnetization as a function of temperature and field. It was found, that furcation temperature, Tf depends on particle size. Keywords: CoCr2O4, superspin-glass like system, hydrothermal method, magnetic properties, oleates
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Variations of actinide magnetism in uranium-base hydrides and other selected systems
Adamska, Anna Maria ; Havela, Ladislav (advisor) ; Arnold, Zdeněk (referee) ; Figiel, Henryk (referee)
Title: Variations of actinide magnetism in uranium-base hydrides and other selected systems. Author: Anna Maria Adamska Department / Institute: Department of Condensed Matter Physics Supervisor of the doctoral thesis: Doc. RNDr. Ladislav Havela, CSc., the Department of Condensed Matter Physics Faculty of Mathematics and Physics Charles University, Prague, Czech Republic and Assoc. Prof. Dr. hab. Nhu-Tarnawska Hoa Kim Ngan, Institute of Physics, Pedagogical University, Kraków, Poland. Abstract: Actinide magnetism was studied in three different types of systems. Variations of magnetic properties of UTGe hydrides as a function of hydrogen concentration prove that doping of U intermetallics by interstitial hydrogen leads to stronger magnetic properties, primarily caused by an increase of the inter-uranium separation. Sputter-deposited UFe2+x films, which are derived from the UFe2 Laves phase but have an amorphous structure, exhibit an increase of the Curie temperarture (to more than 400 K) with the Fe excess, which could not be achieved in the bulk. This is understood as a result of the prominent role of the 3d magnetism of Fe. Notoriously weakly magnetic plutonium was studied in the form of the alloy in the ζ-phase, which exists between 35 and 70 % U in Pu. Its susceptibility increases in a comparison to pure...
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