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Crystal field by the means of single-crystal Time of Flight scattering
Venclík, Štěpán ; Čermák, Petr (advisor) ; Klicpera, Milan (referee)
Crystal electric field has been studied since the 1970s using inelastic neu- tron spectrometry. A simple one-day time-of-flight measurement on pow- dered samples is often used. This thesis aims to demonstrate a method of determination of the crystal electric field parameters based on the data ob- tained from neutron time-of-flight spectrometer on a single crystal. A single crystal of the intermetallic compound PrNi5 was successfully prepared us- ing the floating zone furnace and characterised using XRD, EDX, and Laue diffraction. The time-of-flight scattering on the single crystal was conducted using HYSPEC at ORNL. A Monte Carlo calculation was carried out based on the scattering data to determine the crystal electric field parameters. The usefulness of the time-of-flight scattering on a single crystal for crystal electric field determination, particularly for systems with many crystal field levels, was shown. 1
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Development of crystal structure of (Er,Lu)2(Ti,Zr)2O7 materials
Zelenka, Jiří ; Klicpera, Milan (advisor) ; Kaštil, Jiří (referee)
The present thesis is focused on the development of a crystal structure of A2B2O7 materials, where A is a rare-earth element and B is a transition metal. These materials crystalize generally in four crystallography structures. The thesis is focused on structural transitions from an ordered cubic structure, so-called pyrochlore structure, to a fully disordered cubic structure, so-called defect- fluorite structure, to semi-ordered rhombohedral structure. Compared to previous studies, which dealt with these structural changes in A2Zr2O7 with the substitution of the rare-earth element, this thesis is focused on evolution of structure with a substitution on the B positions. For this research of the crystal structure evolution two series of oxides, Er2(Ti,Zr)2O7 and Lu2(Ti,Zr)2O7, have been selected. Twenty-one samples of those series were prepared by the floating zone method and Czochralski method. Analysis of prepared crystals was performed by using the Laue diffraction method and the powder diffraction methods. For the study, X-ray and neutron diffraction were utilized. A quality of the prepared materials and their crystal structure were studied with the respect to a concentration of Ti-Zr. The development of the crystal structure has been discussed. The thesis will serve as a ground for following research of...
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Preparation and characterization of Lu2Ir2O7 single crystals
Hájek, Filip ; Klicpera, Milan (advisor) ; Prchal, Jiří (referee)
Present thesis is focused on the synthesis and characterization of Lu2Ir2O7 single crystals as a part of a broader study of rare-earth A2Ir2O7 pyrochlore iridates, where A = Y, La-Lu. These materials, crystallizing in the geometrically frustrated pyrochlore lattice and with electronic properties being shaped by strong spin-orbit interaction, have attracted considerable attention of the condensed matter community. The investigation of Lu2Ir2O7 with nonmagnetic Lu3+ cations is crucial in order to reveal the physical properties connected to magnetism of solely the Ir sublattice. The physical properties connected to the Ir sublattice are essential for a proper interpretation of the complex properties of other A2Ir2O7 with magnetic rare-earth cations. For the first time, large good-quality Lu2Ir2O7 single crystals were synthesized by means of the flux method. Their stoichiometry and crystal structure were characterized by means of Laue diffraction and energy-dispersive X-ray technique. Magnetic properties were investigated employing magnetization measurements under ZFC and FC regimes. A bifurcation between ZFC and FC magnetizations was revealed at TIr = 130(1) K, indicating magnetic ordering of the Ir sublattice. Investigating single crystals, the anisotropy effects were studied for the first time. Significantly...
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The search for new spin-liquid materials - synthesis of kagome and pyrochlore fluoride magnetics
Kancko, Andrej ; Colman, Ross Harvey (advisor) ; Klicpera, Milan (referee)
This thesis focuses on the synthesis and characterization of a new AA′ B2F7-type pyrochlore fluoride family, NaCdB2F7 (B = Mn, Fe, Co, Ni, Cu, Zn) predicted by a cal- culated pyrochlore structural tolerance factor, as well as the synthesis of new kagome flu- orides Na3CdCo3AlF14, Rb2SnCo3F12 and Cs2ZrCo3F12, aiming to expand the knowledge about the frustrated pyrochlore and kagome antiferromagnets. The synthesis techniques included solid-state reactions, laser floating zone melting and melt crystallization. All pyrochlore fluorides were successfully synthesized, although only B = Zn, Co, Mn and Ni as phase-pure single crystals. PXRD refinements confirmed the Fd̄3m structure in all synthesized pyrochlores, while SCXRD showed full Na/Cd disorder on the A-site and no A/B intersite mixing in the Co pyrochlore. Magnetization measurements revealed domi- nant antiferromagnetic interactions evidenced by large negative Curie-Weiss temperatures (from -38 K in Mn to -108 K in Co), with a spin-freezing transition below 4 K in B = Co, Mn and Ni, evidenced by further AC susceptibility and heat capacity measurements in Co and Mn. Cu showed no spin freezing down to the lowest-measured temperature, 1.8 K, implying a very large magnetic frustration. Fe has not been measured due to the large impurity content. The...
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Magnetic properties of rare-earth A2Ir207 pyrochlore iridates
Vlášková, Kristina ; Klicpera, Milan (advisor) ; Kempa, Martin (referee) ; Sibille, Romain (referee)
The present thesis is focused on the synthesis, characterisation and magnetic properties of A2Ir2O7 pyrochlore iridates with A standing for Dy - Lu. The geometrically frustrated pyrochlore lattice affects the interactions between magnetic moments of both A3+ and Ir4+ , frequently leading to complex low-temperature states. Moreover, an interplay between spin-orbit coupling and electron correlations, inherent to iridium ions, has been proposed/observed to significantly affect the conductive properties of pyrochlores. The A2Ir2O7 iridates were synthesized, and respective synthesis routes optimized, by CsCl flux method. Thoroughly characterised samples, including previously unprepared A = Tm analogue, were investigated by means of standard bulk methods, as well as techniques of neutron scattering and muon spin resonance. An evolution of magnetic ordering of the iridium sublattice was followed for heavy rare-earth part of the series, allowing to finalize the respective phase diagram. An emergence of oscillations in muon spin rotation spectra unambiguously proved the existence of long-range iridium ordering in studied members. The dynamical AC susceptibility response was discussed in the frame of the model considering weakly bounded spins at the antiferromagnetic domain walls in the material, which appears to be...
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Pressure effects on physical properties of a selected Ce-based compound
Staško, Daniel ; Klicpera, Milan (advisor) ; Míšek, Martin (referee)
Presented thesis focuses on the study of transport properties of two intermetallic compounds, CeRhSi3 and CeCuAl3, under high external pressure. High-pressure dependence of previously reported pressure induced superconductivity in CeRhSi3 is studied closely up to 4.6 GPa, focusing on the, so-far-unstudied, pressure region above 3 GPa. After reaching maximal value at 2.9 GPa, the critical temperature of superconducting transition is gradually suppressed by further pressure application. Extensive search for possible pressure induced superconductivity in CeCuAl3 is conducted, employing solid-pressure-medium Bridgman anvil cells with theoretical pressure limit of 12 GPa. No pressure induced superconductivity is observed up to 4.5 GPa and down to 8 mK. Additionally, a calibration study of three liquid pressure exchange media from Daphne Oil 7000 series is carried out in order to advance high pressure experimental techniques. Comprehensive results about hydrostaticity, solidification, pressure drop and compressibility of individual pressure media are presented.
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The magnetocrystalline anizotropy in the TbTX compounds
Klicpera, Milan
Title: The magnetocrystalline anizotropy in the TbTX compounds Author: Milan Klicpera Department: Department of Condensed Matter Physics Supervisor: doc. Mgr. Pavel Javorský, Dr. Supervisor's e-mail address: javor@mag.mff.cuni.cz Abstract: The subject of this work is the study of structural, magnetic and trans- port properties of the TbNi(Al,In) series to finding connections between magne- tocrystalline anisotropy and lattice parameters of the structure of the TbTX com- pounds. Polycrystalline TbNiAl1−xInx samples were prepared by melting. The phase and crystal structure analysis were provided on samples. We performed the measurements of the magnetization, susceptibility, specific heat, resistivity, low temperature X-ray diffraction and powder neutron diffraction. From the neutron diffraction data we refined lattice parameters and propagation vectors of the series. The main propagation is (000) and second weaker component has the propagation vector (1 2 0 1 2 ). The change of the magnetocrystalline anisotropy from uniaxial to planar type occurs for compounds with x between 0.4 and 0.5. Keywords: magnetization, X-ray and neutron diffraction, electrical resistivity.
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Influence of Fe substitutions on tranformation temperatures in Ni2MnGa alloys
Drastichová, Kristýna ; Klicpera, Milan (advisor) ; Prchal, Jiří (referee)
In this bachelor thesis we are interested in studying the properties of Ni2MnGa alloy and their development with the other element substitution, for example with iron. Overally, we were studying five samples with four different compositions described by the formula Ni50Mn 25Ga25-xFex where the concentration of iron was in the interval . Consequently we performed on the prepared single crystals an extensive characterization by the methods of x-ray and electron diffraction, differential scanning calorimetry and dilatometry. Special emphasis was devoted to measuring the magnetization with vibrational magnetometer. The obtained data enabled us to confirm the quality of the prepared single crystals and to observe a development of Ni2MnGa properties, especially the temperatures of the phase transformations.
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Pressure effects on physical properties of a selected Ce-based compound
Staško, Daniel ; Klicpera, Milan (advisor) ; Míšek, Martin (referee)
Presented thesis focuses on the study of transport properties of two intermetallic compounds, CeRhSi3 and CeCuAl3, under high external pressure. High-pressure dependence of previously reported pressure induced superconductivity in CeRhSi3 is studied closely up to 4.6 GPa, focusing on the, so-far-unstudied, pressure region above 3 GPa. After reaching maximal value at 2.9 GPa, the critical temperature of superconducting transition is gradually suppressed by further pressure application. Extensive search for possible pressure induced superconductivity in CeCuAl3 is conducted, employing solid-pressure-medium Bridgman anvil cells with theoretical pressure limit of 12 GPa. No pressure induced superconductivity is observed up to 4.5 GPa and down to 8 mK. Additionally, a calibration study of three liquid pressure exchange media from Daphne Oil 7000 series is carried out in order to advance high pressure experimental techniques. Comprehensive results about hydrostaticity, solidification, pressure drop and compressibility of individual pressure media are presented.
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