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Synthesis and Characterization of Topological crystalline insulators in the SnTe material class
Chovanec, Jakub ; Uhlířová, Klára (advisor) ; Prokleška, Jan (referee)
k bakalářské práci - Anglický jazyk Synthesis and Characterization of Topological crystalline insulators in the SnTe material class Jakub Chovanec July 21, 2017 In this work we prepared series of single crystal samples PbxSn1−xTe and PbxSn1−xSe. These materials are quite popular last few years, after they were predicted and then char- acterized by [4] as topological crystaline insulators (TCI). TCI is a quantum state of crys- tals, in which symetry causes existance of the metal states on the surface. Samples had been prepared from molten flux and by using Bridgman method. Homogenity and pu- rity of single crystals had been determined. Compounds PbxSn1−xTe and PbxSn1−xSe crystalized in cubical structure and were defined as Fm-3m space group, existance of PbxSn1−xSe in Pnma space group were confirmed. 1
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Extension of instrumental capabilities in cryomagnetic laboratory
Proschek, Petr ; Prokleška, Jan (advisor) ; Javorský, Pavel (referee)
Measurement of elastic properties (thermal expansion and magnetostriction) under (multi)extreme conditions is a difficult task. In the vicinity of the room temperature or above it an abundance of methods is available, with decreasing temperature and adding magnetic field and/or hydrostatic pressure their number is limited. Dilatometric cells (either planparaller or tilted plate design) provide superior sensitivity in low temperatures and applied magnetic fields, however, cannot be used in hydrostatic cell. Common choice for the measurement of thermal expansion under hydrostatic pressure are methods based on strain-gauges, with mediocre sensitivity and more importantly a difficult or even impossible usage at very low temperatures (T ≲ 3 K). Measurement of magnetic properties (especially magnetization) under (multi)extreme conditions is also a difficult task. In the vicinity of temperature 2 K and above it an abundance of methods is available, with decreasing temperature and adding magnetic field and/or hydrostatic pressure their number is limited. VSM system provides great sensitivity, but can not be used under 2 K and hydrostatic pressure. MPMS aparature provides pressure up to 9 GPa (diamond pressure cell), but still we can not apply lower temperatures than 2 K. Our aim is to develop a simple yet sensitive...
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Preparation and characterization of substituted Y ferrites in the form of ceramics and thin films
Pulmannová, Dorota ; Nižňanský, Daniel (advisor) ; Prokleška, Jan (referee)
Title: Preparation and characterization of substituted Y ferrites in the form of ceramics and thin films Author: Dorota Pulmannová Department: Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague Supervisor: RNDr. Daniel Nižňanský, Ph.D. Consultant: Ing. Josef Buršík, CSc. Abstract: In this work we describe a preparation and characterization of a hexagonal ferrite series with composition BaSrCoZnXFe11O22 where X=Fe, Al, Ga, In and Sc. We have prepared these ferrites in the powder and ceramic form using the citrate synthesis and in the thin film form using the chemical solution deposition method. Using the powder neutron diffraction we have found that the sample containing only Fe has collinear magnetic structure that belongs to the C2/m or C2'/m' group. Magnetic structure of the samples substituted with In and Sc is similar, but the magnetic moments of the 18hVI site atoms are not aligned parallely with the other moments. Magnetic structure of Ga-substituted sample is different, it is modulated with a propagation vector k ≈ (0, 0, 3/4). Propagation vector of the Al-substituted ferrite is k ≈ (0, 0, 3/2). Substituting elements show strong preferences for the cation sites. Al and Ga prefer the 3bVI site, Zn prefers the tetrahedral 6cIV and In and Sc prefer the 6cVI site. Room...
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Characterization of RCo2 singlecrystal
Latoňová, Věra ; Prchal, Jiří (advisor) ; Prokleška, Jan (referee)
The bachelor's thesis deals with the characterization of the cubic DyCo2 single crystal along three principal crystallographical orientations. Mea- surements which were so far performed mainly on polycrystals of the RCo2 group were carried out and evaluated. Measurements of electric resistivity, heat capa- city, magnetization and AC susceptibility showed the first-order magnetic phase transition at Curie temperature TC ≈ 142 K. From magnetization curves the easy [100] and the hard [110] axis was determined. Apart from the basic characterizati- on another interesting effects were found: stairlike development of magnetization curves along [100] at 2 K and an unknown anomaly in the phase component of the magnetic susceptibility at 70 K. Measurement of the AC susceptibility in the pa- ramagnetic area performed to check the presence of the so called parimagnetism did not show any anomaly that had been observed by polycrystalline samples - similar to other single crystals. 1
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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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Kritické chování v magnetických fázových diagramech uranových sloučenin
Opletal, Petr ; Prokleška, Jan (advisor)
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
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Studium magnetismu vrstevnatých tetragonálních sloučenin na bázi vzácných zemin a uranu
Bartha, Attila ; Hrůzová Kratochvílová, Marie (advisor) ; Prokleška, Jan (referee)
We have studied the interplay between the layered crystal structure and the 5f magnetism in uranium-based tetragonal compounds UnTIn3n+2. Sin- gle crystals of U2RhIn8, URhIn5 and UIn3 were prepared by In self-flux method. The novel U2RhIn8 compound adopts the Ho2CoGa8-type struc- ture with lattice parameters a = 4.6056(6) ˚A and c = 11.9911(15) ˚A. The behavior of U2RhIn8 strongly resembles that of related URhIn5 and UIn3 with respect to magnetization, specific heat and electrical resistivity except for magnetocrystalline anisotropy developing on stacking composition in the series UIn3 vs. U2RhIn8 and URhIn5. U2RhIn8 orders antiferromagnetically below TN = 117 K and exhibits slightly enhanced Sommerfeld coefficient γ = 47 mJ·mol−1 ·K−2 . TN increases with increasing c/a ratio in contrast to the behavior of their CenTIn3n+2 counterparts. Magnetic field leaves the value of the Néel temperature of URhIn5 and U2RhIn8 unaffected up to 9 T. On the other hand, TN increases with applied hydrostatic pressure up to 3.2 GPa with the ∂TN/∂p coefficient resembling URhIn5 and UIn3. Ther- mal expansion of U2RhIn8 reveals a hysteretic behavior of the antiferromag- netic transition pointing to its 1st -order character. The magnetic structure of URhIn5 obtained from neutron diffraction propagates with k = (1 /2, 1 /2, 1 /2) and the...
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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
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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
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