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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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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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Specific heat of the R2TIn8 compounds
Vlášková, Kristina ; Javorský, Pavel (advisor) ; Svoboda, Pavel (referee)
This thesis deals with magnetic properties of antiferromagnets Nd2TIn8, where T = Rh, Ir and Co. This compounds are members of a group of structurally rela- ted compounds RX3, RTX5 and R2TX8, crystallizing in tetragonal structure, and they reveal interesting magnetic properties, for example there was observed su- perconductivity for Ce-based compounds. In addition there are shown the results of measurement of NdPd5Al2. Specific heat was measured on monocrystals. The order tempratures were determined. The dimensionalities of magnon excitations where estimated using an analysis of low-temperature dependence of specific heat. The magnetic entropies at order temperature were calculated and they were used for determining the ground states of ions Nd3+ and Tm3+ . The treatment of spe- cific heat above the order temperature was used for determining the energy levels of ions in studied compounds. The NdPd5Al2 specific heat was measured at zero and nonzero external fields, this measuring reveals an antiferromagnetic order under the order temperature and the axis of an easy magnetization in direction of c axis. 1
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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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