|
|
Magnetic properties of the spherules from sediment in Tunguska (holocene) and North America (holocene/pleistocene)
Nábělek, Ladislav ; Kletetschka, Günther (advisor) ; Rajmon, David (referee)
In the early 20th century, 30 June 1908, the event took place, which is described as the Tunguska Event, or Tunguska. It is still not entirely clear what happened that day and the whole event was caused. The causes of events Clovis which is dated to the Younger Dryas (YD) are not entirely clear. In this period there was a sharp slowdown, which resulted in the extinction of large mammals. The link between the two events is the discovery of magnetic spherules in the sediment layer. This material may arise in several ways: fossil fuel combustion processes, ablation of cosmic material passing through the atmosphere, a large explosion in the atmosphere or atmospheric discharges (lightning). This thesis deals with analysis and Tunguska Event and Clovis event, and related research microscopic spherules (material of uncertain origin) found after the events in a layer of sediment in North America and central Siberia. The object is to compare the two events and causes of based on research and laboratory measurements of material from Clovis and Tunguska. For the analysis of magnetic spherules status was gained by the non-magnetic separation. The material was measured residual magnetization. The measurements were used magnetic scanner. On the basis of laboratory measurements of magnetic properties of spherules...
|
|
|
Superconductivity and Magnetism of Uranium Compounds
Vališka, Michal
Cílem této práce je studium systému UCo1−xRuxGe nacházejícího se na rozhraní magnetické nestability. Podrobná studie magnetických a transportních vlastností po- lykrystal· s r·zným obsahem ruthenia odhalila komplexní změnu těchto parametr· v rámci celé série. UCoGe je slabý ferromagnet s TC ∼ 3 K a malým magnetickým momentem 0.035 µB/f.u. Pozorovali jsme strmý nár·st těchto hodnot až po hodnotu koncentrace ruthenia xmax ≈ 0.1(TC,max = 9 K a µ0 = 0.11 µB). Podstata tohoto ná- r·stu byla studována na mono krystalu o složení UCo0.88Ru0.12Ge získaném metodou plovoucí zóny. Difrakce polarizovaných neutron· provedená na tomto krystalu se slo- žením UCo0.88Ru0.12Ge vysvětlila posílení magnetismu změnou vzájemné orientace magnetických moment· na iontu uranu a kobaltu. Antiparalelní uspořádání, které bylo dříve publikováno pro UCoGe je změněno na paralelní uspořádání v dopova- ném UCo0.88Ru0.12Ge kdy dojde k reorientaci momentu na kobaltu. Silná anizotropie UCo0.88Ru0.12Ge se promítá do teplotní závislosti odporu a teplotní roztažnosti, které se dramaticky liší pro všechny tři osy. Tento prvotní nár·st TC a magnetického mo- mentu je následován poklesem směřujícím ke koncentraci xcr ≈ 0.31 kde magnetické uspořádání mizí. Podrobná studie kritických exponent· teplotních závislostí elek- trického odporu,...
|
|
|
Structure and magnetic interactions in nanomaterials with application potential
Pacáková, Barbara ; Kalbáčová Vejpravová, Jana (advisor) ; Jirásková, Yvona (referee) ; Svoboda, Pavel (referee)
The thesis is focused on the physics of magnetic nanoparticles (NPs), starting from the solution of magnetic structure, internal alignment within the single particle and role of interactions and particle structure in magnetic response of systems of the NPs. Moreover, the macroscopic arrangement of the NPs and its effect on the properties of system containing the NPs are discussed. The work brings several new results and concepts, such as the solution of magnetic structure of the ε-Fe2O3 phase, methods of proper detection and description of magnetic metal catalyst in carbon nanotubes and role of the NP arrangement and their effect on graphene placed on the top of substrates decorated with the NPs. 1
|
|
|
Solved Problems in Electricity and Magnetism
Jakubská, Iva ; Koupilová, Zdeňka (advisor) ; Šabatka, Zdeněk (referee)
The aim of this Bachelor thesis was to supplement Collection of Solved Problems in Physics, which is developed by Department of Physics Education, with 25 tasks. The tasks are included in the chapters of Electricity and magnetism section. Each task has a structured solution; some tasks are enriched with pictures created by myself. In the Introductory part of this thesis the structure and reasons for choice of the topic of the thesis are described. Next chapter contains basic information about the collection. The third chapter comprises brief comments on the creation process of the tasks. A sample of the five tasks is included in an appendix; the rest is to be found on the enclosed CD or on the collection's website: http://fyzikalniulohy.cz/. In the Conclusion the merits of this Bachelor thesis are summarized. Powered by TCPDF (www.tcpdf.org)
|
|
|
Kritické chování v magnetických fázových diagramech uranových sloučenin
Opletal, Petr ; Prokleška, Jan (advisor) ; Havela, Ladislav (referee)
Title: Critical behavior in magnetic phase diagrams of uranium compounds Author: Bc. Petr Opletal Department: Department of Condensed Matter Physics Supervisor: RNDr. Jan Prokleška, Ph.D., Department of Condensed Matter Physics Abstract: This work is focused on study of phase diagrams and related critical effects in the pseudoternary UCo1-xRuxAl compound. Three single crystals of nominal composition UCo0.99Ru0.01Al, UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al have been prepared by Czochralski method in triarc furnace. Quality of single crystals was checked by EDX analysis, Laue method and XRPD. For UCo0.99Ru0.01Al Curie temperature was determined as TC = 16 K. UCo0.995Ru0.005Al shows transition from paramagnetic to ferromagnetic phase at TC= 4.5 K and at higher temperatures we observe a metamagnetic transition of first order with a critical field HC = 0.04 T. UCo0.9975Ru0.0025Al is paramagnetic to low temperatures with metamagnetic transition of first order and critical field HC = 0.55 T. Experiments in hydrostatic pressure on UCo0.995Ru0.005Al and UCo0.9975Ru0.0025Al showed decay of ferromagnetism and increase of critical field. This behavior is similar to evolution of magnetism in UCoAl and URhAl in applied hydrostatic pressure. Keywords: UCoAl, URuAl, ferromagnetism, metamagnetism
|
|
|
Kooperativní jevy v cerových sloučeninách na hranici magnetismu
Moudřík, Jan ; Prokleška, Jan (advisor) ; Javorský, Pavel (referee)
This work reports on physical properties of a novel CeCo0.715Si2.285 compound. The compound crystallizes in the I-4m2 space group structure with extremely elongated unit cell (a = 4.13˚A , c = 32.84˚A) containing BaAl4 structural patterns. In zero magnetic field it orders antiferromagnetically at TN = 10.0K. Under application of magnetic field along the c-axis it manifests numerous magnetic transitions in small fields (B < 0.5T), resembling the so-called 'devil's staircase' behaviour (e.g. CeSb, CeCoGe3). The magnetization is almost constant from 1T up to 45T for H||c but considerably reduced (0.3µB/Ce) with respect to the free Ce3+ ion. For fields applied along the a-axis typical behaviour for a hard axis in a material with uniaxial anisotropy is observed. The performed single crystal neutron diffraction experiment did not allow complete determination of magnetic structure. 1
|
|
|
Supravodivost a magnetismus uranových sloučenin
Vališka, Michal ; Pospíšil, Jiří (advisor) ; Custers, Jeroen (referee)
Cílem této práce je studium systému UCo1−xRuxGe nacházejícího se na rozhraní magnetické nestability. Podrobná studie magnetických a transportních vlastností po- lykrystal· s r·zným obsahem ruthenia odhalila komplexní změnu těchto parametr· v rámci celé série. UCoGe je slabý ferromagnet s TC ∼ 3 K a malým magnetickým momentem 0.035 µB/f.u. Pozorovali jsme strmý nár·st těchto hodnot až po hodnotu koncentrace ruthenia xmax ≈ 0.1(TC,max = 9 K a µ0 = 0.11 µB). Podstata tohoto ná- r·stu byla studována na mono krystalu o složení UCo0.88Ru0.12Ge získaném metodou plovoucí zóny. Difrakce polarizovaných neutron· provedená na tomto krystalu se slo- žením UCo0.88Ru0.12Ge vysvětlila posílení magnetismu změnou vzájemné orientace magnetických moment· na iontu uranu a kobaltu. Antiparalelní uspořádání, které bylo dříve publikováno pro UCoGe je změněno na paralelní uspořádání v dopova- ném UCo0.88Ru0.12Ge kdy dojde k reorientaci momentu na kobaltu. Silná anizotropie UCo0.88Ru0.12Ge se promítá do teplotní závislosti odporu a teplotní roztažnosti, které se dramaticky liší pro všechny tři osy. Tento prvotní nár·st TC a magnetického mo- mentu je následován poklesem směřujícím ke koncentraci xcr ≈ 0.31 kde magnetické uspořádání mizí. Podrobná studie kritických exponent· teplotních závislostí elek- trického odporu,...
|
|
|
Determination of crystal field parameters in selected tetragonal compounds
Zubáč, Jan ; Javorský, Pavel (advisor) ; Prchal, Jiří (referee)
The thesis deals with a crystal electric field and its effect on magnetic properties of the in- termetalic tetragonal rare-earth compounds. Using the self-flux method we have prepared single crystals of two R2TIn8 type compounds, namely Nd2RhIn8 and Nd2IrIn8. These compounds or- der antiferromagnetically in low-temperature region. We have verified a proper structure through EDX analysis, X-ray powder diffraction and Laue diffraction method. Calculations of the crystal field parametres based on experimental magnetic susceptibilities data were performed. Apart from Nd2RhIn8, we have computed crystal field parameters for isostructural Nd2CoIn8 and Dy2CoIn8 compounds and cerium compound CeCuAl3. These compounds are studied simultaneously at our department.
|
|
|
Studium magnetických kvantově kritických jevů na uranových sloučeninách
Opletal, Petr ; Pospíšil, Jiří (advisor) ; Javorský, Pavel (referee)
Motivation of this thesis is a study of magnetic phase diagram of the pseu- doternary system UCoxRu1−xAl. Three single crystals UCo0.19Ru0.81Al, UCo0.27Ru0.73Al and UCo0.40Ru0.60Al have been successfully prepared by Czochralski method. Composition was confirmed by EDX analysis and quality of single crystals was checked by Laue method. Crystallographic parameters and occupancies were de- termined by X-ray powder diffraction. Data analysis confirmed strong uniaxial magnetocrystalline anisotropy (c is the easy magnetization axis) and existence of hard and soft ferromagnetic phase. Curie temperature TC = 41 K was determined for UCo0.40Ru0.60Al and phase transition from the soft ferromagnetic phase to the hard one takes place at 35 K. UCo0.27Ru0.73Al becomes ferromagnetic at TC = 18 K and the transition from the soft to the hard ferromagnetic phase takes place somewhere around 7 K. UCo0.19Ru0.81Al is paramagnetic down to 2 K. Analysis of the temperature dependence of resistivity and heat capacity reveals signatures of non-Fermi liquid behaviour due to proximity of quantum critical point. 1
|
|
|
Studium magnetismu ve sloučeninách CeTX3
Moudřík, Jan ; Prokleška, Jan (advisor) ; Javorský, Pavel (referee)
Solid solutions of BaNiSn3 type CeTX3 (T and X denote a transition met- al and Si/Ge, respectively) compounds were studied. Polycrystalline samples of solid solutions CeCoxRh1−xSi3 (x = 0.5, x = 0.8, x = 0.9 and x = 1.0) and CeIr(SixGe1−x)3 (x = 0.1, x = 0.4, x = 0.6 and x = 0.8) were successfully grown. A superconducting transition at 0.7-0.9 K was exhibited by all four compositions of the solution CeCoxRh1−xSi3. Based on measurements of specific heat, we con- clude that the superconductivity is probably caused by impurity phases. We have determined crystallographic, thermodynamic and magnetic properties of the solu- tion CeIr(SixGe1−x)3. Magnetic phase transition temperatures were established, the character of the transitions changed significantly in all four compositions, the temperatures themselves did not. 1
|
guest ::
