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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
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Elektronové vlastnosti sloučenin RPd5Al2
Zubáč, Jan ; Javorský, Pavel (advisor) ; Čermák, Petr (referee)
We have studied magnetic properties of the intermetallic NdPd5Al2 com- pound by means of specific heat and magnetization measurements and neutron scattering. The compound crystallizes in the tetragonal I4/mmm space group with lattice parameters a =4.147 ˚A and c =14.865 ˚A, orders antiferromagnet- ically below TN =1.3 K and presents large magnetocrystalline anisotropy due to the crystal-field effects. The obtained magnetic phase diagram is charac- terized by two distinct magnetically ordered phases similarly to structurally re- lated tetragonal RTX5 and R2TX8 compounds. The zero-field antiferromagnetic phase is characterized by the propagation vector k = (1 2 00) and antiferromag- netic coupling of Nd moments along the teragonal c-axis with the amplitude of magnetic moments of 2.22 µB/Nd as was revealed by neutron diffraction. The transition from the paramagnetic to magnetically ordered in zero field is the first-order phase transition. The CF excitations in NdPd5Al2 were detected by means of INS at 3.0 meV, 7.4 meV, 8.6 meV and 17.1 meV. We further compare our findings about CF in NdPd5Al2 obtained from INS, susceptibility analysis and first-principles calculations and confront them with the experimental mag- netization and magnetic specific heat data. Our results will be also discussed with respect to related...
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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.
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The development of magnetic behavior in the PrNi1-xCuxAl compounds
Fikáček, Jan ; Javorský, Pavel (advisor) ; Prchal, Jiří (referee)
In the present work we studied magnetic properties of the substituted PrNi1-xCuxAl series. A very interesting behavior had been reported in the previously studied systems with the same substitution, but with different rare earths contained, e.g. loss of long range order for certain concentrations of copper. We prepared polycrystalline samples of the PrNi1-xCuxAl (x = 0.1 - 0.9, 9 different stoichiometries) and measured them using X-ray diffraction, specific heat, magnetization and AC susceptibility. Additionally, powder neutron diffraction measurement on PrNi0.2Cu0.8Al sample was performed in ILL (Institut Laue Langevin) in Grenoble. Results of measurements on these compounds show on the presence of a long order in case of compounds with x = 0.1 - 0.4 below the ordering temperatures in the range of 3.4 - 5 K. Measurements of AC susceptibility and neutron diffraction revealed the loss of long range order in the rest of the series. In these compounds, the development of a spin glass state occurs below the temperatures between 3.4 and 4.5 K.
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Magnetic excitations in cerium compounds
Vlášková, Kristina ; Javorský, Pavel (advisor) ; Prchal, Jiří (referee)
Title: Magnetic excitations in cerium compounds Author: Kristina Vlášková Department: Department of Condensed Matter Physic Supervisor: doc. Mgr Pavel Javorský, Dr., Department of Condensed Matter Physics Abstract: Thanks to presence of only one electron in 4f shell of cerium ion, Ce based compounds reveal wide range of exceptional magnetic properties like valence fluctuations, magnetic ordering or spin glass behavior. In present thesis we mainly focus on tetragonal CeCuxAl4-x system and its magnetic behavior. Former results of inelastic neutron experiments opened discussion about energy levels of cerium ions in CeCuAl3. Except two crystal field excitations also one additional energy level was present, phenomenon of vibron quasi-bound state was proposed to explain observed energy structure. Measurement and analysis of specific heat and neutron inelastic scattering on compounds with various Cu content should help to understand phenomenon of vibron state and also its development with Cu/Al concentration. Another two types of cerium compounds will be investigated in means of specific heat and resistivity measurement, polycrystalline sample of CePt4Al and single crystal of Ce3Ru4Al12. Preparation, characterization and measurement of low temperature properties are subjects of this work. Results will be discussed...
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