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Study of proper and improper microwave dielectric losses by means of teraherz and infrared spectroscopy
Tkáč, Ondřej ; Kamba, Stanislav (advisor) ; Petzelt, Jan (referee)
Title: Study ol"proper and improper microwave dielectric tosses by means of tcrahcrz and infrared speetroseopy Author: Ondfej Tkac Department: Department of Dielectrics. Institute of Physics, Academy of Sciences of C/ech Republic Supervisor: RNDr. Slanislav Kamba.C'Sc.. Na Slovance 2. Prague 8 Supervisor's e-mail adress: kambawT/u.c/ Abstract: In the llrst part of this thesis there is described relevant theory, especially we pay our attention to the principles of infrared speetroseopy and fitting models, then to the explanation of the terms proper and improper dielectric losses and we also discuss dielectrics and ferroelectrics. By means of Fourier transform infrared speetroseopy we measured infrared spectra at room temperature in the range of 30 - 3000 em"1. We lilted the spectra and then we extrapolated the final complex permit!vity into the microwave range. This enabled us to estimate the proportion of improper dielectric losses on total microwave losses. By the ceramic SiVxPlxCeVfinO-^ (.\0 to 9) we studied the impact of amount of lead on dielectric properties. We found out that the substitution of strontium with lead causes the increase of permitivity up lo several thousands and forces ferroelectric transition for x>2. With perovskitc Ca/n, jNb^ :,-xVx(.)1 (.v=0 to 0,01) we examined the inlluence of...
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Spin and Lattice Excitations in Multiferroics
Skiadopoulou, Styliani ; Kamba, Stanislav (advisor) ; Bordács, Sándor (referee) ; Hlídek, Pavel (referee)
The scientific significance of dynamical magnetoelectric coupling, combined with the eminent implication of its technological applications, prompted our investigation of spin and lattice excitations of a series of widely known, as well as entirely novel, multiferroic materials. The magnetoelectric excitations of the celebrated room temperature multiferroic BiFeO3 were investigated. Among the previously reported, two new infrared active spin excitations were discovered. Polar phonons in BiFeO3 ceramics, as well as in a thin film epitaxially grown on TbScO3 substrate, were investigated in a broad temperature range. The novel double perovskite Pb2MnTeO6 was prepared and described for the first time. Its crystal and magnetic structure classify it in the rare family of antipolar antiferromagnets. The spin-induced colossal magnetoelectric effect in Ni3TeO6 stimulated us to discover electromagnons in this material and to prepare and study Mn and Co doped samples. All Ni3-xBxTeO6 (B=Mn, Co) compounds present the non-centrosymmetric R3 space group symmetry, collinear antiferromagnetic spin structure, and spin-induced electric polarization below TN. . Mn-doping results in increase of the Néel temperature, whereas Co-doping in decrease of the magnetic field value of the spin-flop transition, at which the...
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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...
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Spin and Lattice Excitations in Multiferroics
Skiadopoulou, Styliani ; Kamba, Stanislav (advisor) ; Bordács, Sándor (referee) ; Hlídek, Pavel (referee)
The scientific significance of dynamical magnetoelectric coupling, combined with the eminent implication of its technological applications, prompted our investigation of spin and lattice excitations of a series of widely known, as well as entirely novel, multiferroic materials. The magnetoelectric excitations of the celebrated room temperature multiferroic BiFeO3 were investigated. Among the previously reported, two new infrared active spin excitations were discovered. Polar phonons in BiFeO3 ceramics, as well as in a thin film epitaxially grown on TbScO3 substrate, were investigated in a broad temperature range. The novel double perovskite Pb2MnTeO6 was prepared and described for the first time. Its crystal and magnetic structure classify it in the rare family of antipolar antiferromagnets. The spin-induced colossal magnetoelectric effect in Ni3TeO6 stimulated us to discover electromagnons in this material and to prepare and study Mn and Co doped samples. All Ni3-xBxTeO6 (B=Mn, Co) compounds present the non-centrosymmetric R3 space group symmetry, collinear antiferromagnetic spin structure, and spin-induced electric polarization below TN. . Mn-doping results in increase of the Néel temperature, whereas Co-doping in decrease of the magnetic field value of the spin-flop transition, at which the...
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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...
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Study of proper and improper microwave dielectric losses by means of teraherz and infrared spectroscopy
Tkáč, Ondřej ; Kamba, Stanislav (advisor) ; Petzelt, Jan (referee)
Title: Study ol"proper and improper microwave dielectric tosses by means of tcrahcrz and infrared speetroseopy Author: Ondfej Tkac Department: Department of Dielectrics. Institute of Physics, Academy of Sciences of C/ech Republic Supervisor: RNDr. Slanislav Kamba.C'Sc.. Na Slovance 2. Prague 8 Supervisor's e-mail adress: kambawT/u.c/ Abstract: In the llrst part of this thesis there is described relevant theory, especially we pay our attention to the principles of infrared speetroseopy and fitting models, then to the explanation of the terms proper and improper dielectric losses and we also discuss dielectrics and ferroelectrics. By means of Fourier transform infrared speetroseopy we measured infrared spectra at room temperature in the range of 30 - 3000 em"1. We lilted the spectra and then we extrapolated the final complex permit!vity into the microwave range. This enabled us to estimate the proportion of improper dielectric losses on total microwave losses. By the ceramic SiVxPlxCeVfinO-^ (.\0 to 9) we studied the impact of amount of lead on dielectric properties. We found out that the substitution of strontium with lead causes the increase of permitivity up lo several thousands and forces ferroelectric transition for x>2. With perovskitc Ca/n, jNb^ :,-xVx(.)1 (.v=0 to 0,01) we examined the inlluence of...
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