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Pressure-induced changes of magnetic behavior of RCo2-type compounds
Valenta, Jaroslav ; Prchal, Jiří (advisor) ; Kamarád, Jiří (referee)
The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.
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Influence of the external pressure on the magnetic behavior of the material
Valenta, Jaroslav ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
This thesis deals with magnetic properties of the HoCo2 compound, which is composed of rare earth and transition metal elements. The study is focused on properties at ambient pressure and changes of the magnetic behavior of the material under hydrostatic pressure. At the ambient pressure, there was performed analysis of the sample quality with a finding of presence of three magnetic transitions: flipping temperature magnetization of Co clusters Tf = (125 ± 1) K, Curie temperature TC = (79,5 ± 0,1) K and spin-reorientation temperature TR = (16,4 ± 0,5) K. When applying the hydrostatic pressure up to 3 GPa, there was observed a shift of the temperatures of the magnetic transitions and in the case Tf and TR their consequent vanishing. From the shifts of the TC and Tf towards lower temperatures and from the vanishing of the Tf, it was concluded that Co magnetism is being suppressed by the influence of the hydrostatic pressure.
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Design of equipment for hydrostatic pressure monitoring
Zahrádka, Michal ; Bražina, Jakub (referee) ; Pruša, Radomír (advisor)
The purpose of bachelor thesis is the design and manufacture of a leveling electronic hydrostatic device. Part of the thesis is a research for current leveling equipment and pressure measurement methods with emphasis on the measurement of hydrostatic pressure. The entire device is to be implemented on the Arduino development platform. The use of the assembled meter is assumed in the construction industry.
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Measuring of height liquid level
Koksa, Martin ; Hůlka, Tomáš (referee) ; Němec, Zdeněk (advisor)
This bachelor‘s thesis seeks to clarify and describe modern methods of measuring a liquid level. The topic is discussed from several points of view, from which the emphasis was put on the division according to usage in hydropower. Moreover, this thesis portrays the fundamental principles of hydroelectric power plants and sensors used in them.
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Pressure-induced changes of magnetic behavior of RCo2-type compounds
Valenta, Jaroslav
The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.
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Structural changes in intermetallic compounds
Doležal, Petr ; Prchal, Jiří (advisor)
This diploma thesis is focused on the study of the structural phase transitions in intermetallic compounds LaPd2(Al,Ga)2 by low-temperature x-ray powder diffraction and macroscopic measurements on single crystals. The results obtained from powder diffraction at room temperature confirm that the compounds crystallize in tetragonal CaBe2Ge2 structure type (space group P4/nmm). At low temperature all the compounds undergo the same structural phase transition by lowering the symmetry to the orthorhombic space group Cmma. Although the structural transformation is of first order, the transition is not-manifested in step-like change of the phase at a certain temperature, but occurs in a broader temperature interval. In this interval the different phases coexist and transform gradually from high- to low- temperature phase. After application of hydrostatic pressure the structural transition is shifted to higher temperatures. Despite that the low temperature structures are of the same type, there is a difference between compounds containing Ga and Al in the discontinuity of the lattice parameters resulting in a distinct anomaly in electrical resistivity. In pressures >0.6 GPa this characteristic anomaly on single crystalline CePd2Al2 is changed, indicating a pressure- induced change of the low-temperature...
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The Technical Monuments in Třeboň Region And How to Use Them in Primary School Education
ŠIMÁČKOVÁ, Jindřiška
The topic of this thesis is called "Technical Landmarks in the Třeboňsko Region and their Application in First Grade Primary School Education." The theoretical part focuses on project teaching and the competencies of the first grade primary school pupil in the area of technical education according to the FEP for basic education, chapter "Humans and Their World (Člověk a jeho svět)". Furthermore, this thesis deals with technical landmarks in the Třeboňsko region. The practical part contains several technical landmarks which may be used as inspiration when creating educational projects for structural and technical education. Some of these projects have been applied in teaching in a small-class primary school. The final part of the thesis contains questionnaires given to first grade primary school teachers to test the indicative functionality of these projects.
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Magnetism in the RCo2-type compounds
Šebesta, Jakub ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
Magnetic properties of RCo2 compounds have been studied since the sec- ond half of the last century. However, there was recently observed new mag- netic state, so-called parimagnetism. The aim of this thesis was to find the real behavior of TmCo2, which exhibits many discrepancies in the published results, by means of preparation of high-quality single-crystals, its characteri- zation around the ordering temperature and to study parimagnetic behavior. Obtained results showed differences between the samples, which should be caused by the instability of Co and Tm magnetism. It might be the reason of discrepancies in the literature. The results however show the same struc- ture of measured curves with two present phase transition. We suggest two possible interpretations: a) magnetic reorientation of Tm magnetic moments below the ordering temperature of the Tm sub-lattice or b) consequent or- dering of the rare-earth sub-lattice followed by ordering of the Co sub-lattice at lower temperature, which seems to be more realistic. We observed pari- magnetic anomalies at 38 K, 80 K, 168 K only in the case of single-crystals containing small amount of impurity phase, which probably affects the for- mation of magnetic clusters. 1
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