|
|
Properties of novel magnetoelectric and multiferroic ceramic materials
Osička, Luděk ; Kachlík, Martin (referee) ; Maca, Karel (advisor)
Literature search about properties of magnetoelectric and multiferroic ceramic materials was made. Ferromagnetism and ferroelectricity and requirements for materials in which both of these properties can exist in the same phase were discussed. Further, multiferroics were classified by mechanism of ferroelectricity and by their crystal structure. Finally, multiferroic and magnetoelectric composites and some examples of strong magnetoelectric effect in multiferroics were described. In experimental part of this bachelor thesis preparation of specimens of magnetoelectric perovskite EuTiO3 was described. Prepared specimens had higher density than specimens described in literature and were phase-pure and they are suitable for research of magnetoelectric properties of EuTiO3 by infrared spectroscopy.
|
|
|
Processing and properties of novel magnetoelectric and multiferroic ceramic materials
Osička, Luděk ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
A literature review on the topic of ferroic and multiferroic solid solutions of BaTiO3, SrTiO3 and EuTiO3 forms the first part of this master thesis. The second part describes the experimental preparation and evaluation of the properties of samples of europium strontium titanates - EuxSr1-xTiO3. First, the high temperature solid state synthesis was carried out and relative density and open porosity of the sintered samples were evaluated. The sintered samples showed open porosity higher than 10%. The reasons for this behavior were evaluated and described from the point of view of experimental conditions and thermodynamical calculations. Finally, electric and dielectric properties of selected samples were measured. These results show that these samples are insulators and their residual conductivity is caused probably by oxygen vacancies, arising from the synthesis in a strongly reducing atmosphere of pure hydrogen.
|
|
|
Infrared Spectroscopy of Multiferroics
Goian, Veronica ; Kamba, Stanislav (advisor) ; Javorský, Pavel (referee) ; Dubroka, Adam (referee)
Infrared Spectroscopy of Multiferroics Author: Veronica Goian Institute: Department of Dielectrics, Institute of Physics of the Academy of Sciences, Na Slovance 2, 182 21 Prague 8 Abstract: We have investigated numerous multiferroic and magnetoelectric materials mainly using infrared (IR) spectroscopy. Nevertheless, the studies were frequently combined with radio-frequency, microwave, THz, Raman and structural measurements provided by our colleagues, as well as by magnetic and elastic investigations, where we participated. Our main aim was the complex study of quantum-paraelectric antiferromagnet EuTiO3 in the form of crystals, ceramics and thin films. Near 300 K we have discovered an antiferrodistorive phase transition from cubic mPm3 to tetragonal I4/mcm structure in bulk EuTiO3 and explained its low-frequency dielectric properties by anomalous polar phonon behavior. Large and anisotropic magnetodielectric effect, which we found in EuTiO3, was successfully explained and experimentally confirmed by observation of tuning of phonon frequency with magnetic field. Our IR studies of tensile strained EuTiO3 thin films revealed a displacive ferroelectric phase transition near 250 K. Our American colleagues revealed the ferromagnetic order below 4.2 K in the same strained EuTiO3 thin film. In such way we have...
|
|
|
Hyperfine interactions in multiferroics containing iron
Kmječ, Tomáš ; Kohout, Jaroslav (advisor)
Multiferroic materials, in which spontaneous orderings (especially magnetic and electrical, in some cases elastic) jointly exist and may mutually interact, are currently in the center of attention in many fields of research due to their high application potential. They are already used in many applications, as in various sensors, microwave filters or electro / magneto- mechanical manipulators and actuators. Nevertheless, many features of microstructure and moment arrangements are not yet fully explained and understood. The presented work is mostly experimental and focuses on the investigation of several promising multiferroic materials: Pb1 − xBax(Fe0.5Nb0.5)O3 (x = 0 - 1) and Pb(Fe0.5Sb0.5)O3 with a perovskite structure and labeled as multiferroics of the I. type according to the Khomsky classification, BaYFeO4, which belongs to the multiferroics of the II. Khomsky class, and LiFePO4, which is a potentially multiferroic substance containing Fe2+ and are used in electric accumulators at present. Mössbauer spectroscopy of the 57 Fe isotope was used as a key experimental method, which can provide new information about the local arrangement in the vicinity of resonantly absorbing nuclei in the investigated substances. Data evaluation and interpretation would not be possible without the using results...
|
|
|
Hyperfine interactions in multiferroics containing iron
Kmječ, Tomáš ; Kohout, Jaroslav (advisor) ; Mašláň, Miroslav (referee) ; Šepelák, Vladimír (referee)
Multiferroic materials, in which spontaneous orderings (especially magnetic and electrical, in some cases elastic) jointly exist and may mutually interact, are currently in the center of attention in many fields of research due to their high application potential. They are already used in many applications, as in various sensors, microwave filters or electro / magneto- mechanical manipulators and actuators. Nevertheless, many features of microstructure and moment arrangements are not yet fully explained and understood. The presented work is mostly experimental and focuses on the investigation of several promising multiferroic materials: Pb1 − xBax(Fe0.5Nb0.5)O3 (x = 0 - 1) and Pb(Fe0.5Sb0.5)O3 with a perovskite structure and labeled as multiferroics of the I. type according to the Khomsky classification, BaYFeO4, which belongs to the multiferroics of the II. Khomsky class, and LiFePO4, which is a potentially multiferroic substance containing Fe2+ and are used in electric accumulators at present. Mössbauer spectroscopy of the 57 Fe isotope was used as a key experimental method, which can provide new information about the local arrangement in the vicinity of resonantly absorbing nuclei in the investigated substances. Data evaluation and interpretation would not be possible without the using results...
|
|
|
Local structure of hexagonal ferrites studied by NMR
Kouřil, Karel ; Štěpánková, Helena (advisor) ; Pištora, Jaromír (referee) ; Schneeweiss, Oldřich (referee)
Title: Local structure of hexagonal ferrites studied by NMR Author: Karel Kouřil Department/Institute: Department of Low Temperature Physics Supervisor of the doctoral thesis: prof. RNDr. Helena Štěpánková, CSc. Abstract: Hexagonal ferrites of M, W, X and Y structure types were studied by means of NMR, electronic structure calculations and magnetoelectric experi- ments. Presented results deal with cation distribution, localization of ferrous ions, interpretation of NMR spectra of studied materials and effects of size reduction. In oriented layers M type strontium ferrite and submicron particles of M type barium ferrite pronounced effects of reduced size were observed on 57 Fe NMR spectra. Performance of magnetoelectric barium-strontium Y type hexaferrites with divalent zinc cations improved upon thermal treatment of samples while distribution of zinc was not significantly altered. In Sc sub- stituted BaM, Sc content was found to be uniform throughout TSSG grown crystal. In LaSrM systems electron localization in 2a sublattice was observed, co-substitution with La+Zn, La+Co and La+Cu was found to lead to partial charge compensation. In strontium ferrites of type W and X localization of ferrous ions in octahedral sites in SS block pair was observed. Keywords: NMR, hexagonal ferrites, structure,...
|
|
|
Infrared Spectroscopy of Multiferroics
Goian, Veronica ; Kamba, Stanislav (advisor) ; Javorský, Pavel (referee) ; Dubroka, Adam (referee)
Infrared Spectroscopy of Multiferroics Author: Veronica Goian Institute: Department of Dielectrics, Institute of Physics of the Academy of Sciences, Na Slovance 2, 182 21 Prague 8 Abstract: We have investigated numerous multiferroic and magnetoelectric materials mainly using infrared (IR) spectroscopy. Nevertheless, the studies were frequently combined with radio-frequency, microwave, THz, Raman and structural measurements provided by our colleagues, as well as by magnetic and elastic investigations, where we participated. Our main aim was the complex study of quantum-paraelectric antiferromagnet EuTiO3 in the form of crystals, ceramics and thin films. Near 300 K we have discovered an antiferrodistorive phase transition from cubic mPm3 to tetragonal I4/mcm structure in bulk EuTiO3 and explained its low-frequency dielectric properties by anomalous polar phonon behavior. Large and anisotropic magnetodielectric effect, which we found in EuTiO3, was successfully explained and experimentally confirmed by observation of tuning of phonon frequency with magnetic field. Our IR studies of tensile strained EuTiO3 thin films revealed a displacive ferroelectric phase transition near 250 K. Our American colleagues revealed the ferromagnetic order below 4.2 K in the same strained EuTiO3 thin film. In such way we have...
|
|
|
Processing and properties of novel magnetoelectric and multiferroic ceramic materials
Osička, Luděk ; Pouchlý, Václav (referee) ; Maca, Karel (advisor)
A literature review on the topic of ferroic and multiferroic solid solutions of BaTiO3, SrTiO3 and EuTiO3 forms the first part of this master thesis. The second part describes the experimental preparation and evaluation of the properties of samples of europium strontium titanates - EuxSr1-xTiO3. First, the high temperature solid state synthesis was carried out and relative density and open porosity of the sintered samples were evaluated. The sintered samples showed open porosity higher than 10%. The reasons for this behavior were evaluated and described from the point of view of experimental conditions and thermodynamical calculations. Finally, electric and dielectric properties of selected samples were measured. These results show that these samples are insulators and their residual conductivity is caused probably by oxygen vacancies, arising from the synthesis in a strongly reducing atmosphere of pure hydrogen.
|
|
|
Properties of novel magnetoelectric and multiferroic ceramic materials
Osička, Luděk ; Kachlík, Martin (referee) ; Maca, Karel (advisor)
Literature search about properties of magnetoelectric and multiferroic ceramic materials was made. Ferromagnetism and ferroelectricity and requirements for materials in which both of these properties can exist in the same phase were discussed. Further, multiferroics were classified by mechanism of ferroelectricity and by their crystal structure. Finally, multiferroic and magnetoelectric composites and some examples of strong magnetoelectric effect in multiferroics were described. In experimental part of this bachelor thesis preparation of specimens of magnetoelectric perovskite EuTiO3 was described. Prepared specimens had higher density than specimens described in literature and were phase-pure and they are suitable for research of magnetoelectric properties of EuTiO3 by infrared spectroscopy.
|
guest ::
