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Nuclear magnetic resonance study of multiferroic perovskites
Adamec, Martin ; Chlan, Vojtěch (advisor) ; Kouřil, Karel (referee)
The aim of this Bachelor thesis is to study the oxide Pb(FeNb)0.5O3 by means of nuclear magnetic structure spectroscopy. Studied material has perovskite structure and belongs to a class of materials exhibiting magnetoelectric behavior. Temperatures of phase transitions are among others affected by selection of cations and their arrangement. To examine the structural properties, nuclear magnetic resonance was utilized, since this method is sensitive to electron and magnetic structure. Temperature dependence (in the range of 12 to 296K) of 207 Pb and 93 Nb spectra sample Pb (FeNb)0.5O3 was measured in external magnetic field 9.4T. The spectra show frequency shifts and resonance-line width increase with decreasing temperature. 57 Fe spectrum was measured in zero external field at 4.2 K. Multiple signals were detected, indicating the presence of more than one type of Fe atom in the structure. The experimental results are interpreted and discussed in relation to phase transitions and to cation arrangement in the sample.
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Hyperfine Interactions in Ferrites with Spinel Structure
Chlan, Vojtěch
Title: Hyperfine Interactions in Ferrites with Spinel Structure Author: Vojtěch Chlan Faculty of Mathematics and Physics, Charles University in Prague Supervisor: Prof. RNDr. Helena Štěpánková, CSc. Abstract: Ferrite systems with spinel structure, manganese ferrite, lithium ferrite and magnetite, are studied experimentally by nuclear magnetic resonance (NMR) spectroscopy and from the first principles by electron structure calculations based on density functional theory (DFT). Manganese ferrites with various degrees of manganese-iron inversion and with different manganese contents are investigated, with respect to magnetic structure and cationic arrangement. An approach for NMR spectra interpretation is elaborated on ordered lithium ferrite, consisting in matching the calculated hyperfine field anisotropy with experimental results. This method is then applied to low temperature structure of magnetite, showing a promising path towards solving its complicated structure, orbital and charge ordering. The switching of magnetic easy axis induced by external magnetic field is observed in magnetite and the accompanying structural changes are studied by means of magnetic and NMR measurements. Magnetite with cationic vacancies is investigated by analyzing satellite structure induced by the vacancies; it is shown that...
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