Zur Kurzanzeige

Investigation of the Structure and Dynamics of Multiferroic Systems by Inelastic Neutron Scattering and Complementary Methods

dc.contributor.advisorEckold, Götz Prof. Dr.
dc.contributor.authorZiegler, Fabian
dc.date.accessioned2019-02-22T10:23:29Z
dc.date.available2019-02-22T10:23:29Z
dc.date.issued2019-02-22
dc.identifier.urihttp://hdl.handle.net/11858/00-1735-0000-002E-E5A6-5
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-7307
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-7307
dc.language.isoengde
dc.publisherNiedersächsische Staats- und Universitätsbibliothek Göttingende
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject.ddc540de
dc.titleInvestigation of the Structure and Dynamics of Multiferroic Systems by Inelastic Neutron Scattering and Complementary Methodsde
dc.typedoctoralThesisde
dc.contributor.refereeEckold, Götz Prof. Dr.
dc.date.examination2018-12-12
dc.description.abstractengThe aim of this thesis is the characterization of three different multiferroic materials. The first substance is MnWO4 whose magnetic phase transition temperatures can be increased when tungsten atoms are substituted by molybdenum. However, it is unclear how far the transition temperatures can be increased. The first part of the thesis therefore aims at the determination of the maximum doping concentration by x ray powder diffraction and the maximum transition temperature by impedance spectroscopy. It is indeed possible to synthesize a metastable wolframite phase with up to 65 % molybdenum, but these samples decompose during sintering as preparation for impedance measurements. The phase transition temperatures of samples with unusual high Mo content could therefore not be determined. This decomposition of sintered samples indicates that the thermodynamic ground state at high temperatures is a miscibility gap, which allows to solve 30 % molybdenum in the wolframite phase. In the second part of this thesis, magnon spectra were measured by inelastic neutron scattering in the multiferroic phase of CuO as well as in the paraelectric, antiferromagnetic phase for comparison. This research is motivated by the recent discovery of an electromagnon in the multiferroic phase. Two distinct excitations are identified in this phase. The first one is a phason mode where the spins rotate inside the cycloidal plane and that has no spin gap within the instrumental resolution. The second mode might indeed be the electromagnon, because the determined eigenvector matches the predicted displacement pattern. Furthermore, the spin gap of this second mode has exactly the same value as the published excitation energy of the electromagnon. The aim of the third part of this thesis is to answer the question whether Bi2Mn4O10 is multiferroic. Therefore, the dielectric permittivity of Bi2Mn4O10 was measured in a range of temperatures above and below TN. There is a small but well defined peak-like anomaly along the b-axis, which is evidence for the onset of ferroelectricity. The multiferroic coupling mechanism that is proposed to induce ferroelectricity in R2Mn4O10 involves the displacement of Mn-atoms. In order to answer the question if this mechanism can also be applied to Bi2Mn4O10, all elastic constants were determined in the multiferroic phase as well as at room temperature for comparison. There is, however, no observable temperature-dependent anomaly.de
dc.contributor.coRefereeStalke, Dietmar Prof. Dr.
dc.subject.engmultiferroicde
dc.subject.engCuOde
dc.subject.engMnWO4de
dc.subject.engBi2Mn4O10de
dc.subject.engneutron spectroscopyde
dc.subject.engimpedance spectroscopyde
dc.subject.engx-ray powder diffractionde
dc.subject.enginelastic neutron scatteringde
dc.subject.engelastic constantsde
dc.subject.engelectromagnonde
dc.subject.engmagnonde
dc.subject.engantiferromagneticde
dc.subject.engRaman spectroscopyde
dc.subject.engdielectric permittivityde
dc.subject.engphononde
dc.identifier.urnurn:nbn:de:gbv:7-11858/00-1735-0000-002E-E5A6-5-2
dc.affiliation.instituteFakultät für Chemiede
dc.subject.gokfullChemie  (PPN62138352X)de
dc.identifier.ppn1054637687


Dateien

Thumbnail

Das Dokument erscheint in:

Zur Kurzanzeige