No description available.

Title: Optical and magneto-optical studies of ferrimagnetic garnets for photonic and spintronic applications Author: RNDr. Lukáš Beran Department: Intitute of Physics of Charles University Supervisor: RNDr. Martin Veis, PhD., Institute of Physics of Charles University Abstract: This doctoral thesis is devoted to fabrication and systematic char- acterization of physical properties of thin films of iron garnets with potential applications in photonic and spintronic devices. Investigated samples were pre- pared by metallo-organic decomposition and pulsed laser deposition. The study was focused on structural and magnetic characterizaiton along with optical and magneto-optical properties. Obtained experimental results were further con- fronted with theoretical calculations. The application potencial of garnets for photonic devices was discussed based on determined Figure of Merit (Faraday rotation to optical loss ratio). High values were achieved for single crystal thin film of Ce doped yttrium iron garnet on galium gadolinium garnet substrate as well as for pollycrystalline Bi doped yttrium iron garned on silicon substrate. Furthermore, new rare-earth garnets were prepared with attempt to achieve per- pendicular magnetic anisotropy of these film. This was achieved for three di erent materials, which were not...

The aim of this master thesis is to prepare and systematically characterize two groups of ultra-thin films of iron garnets with different compositions and deposition conditions. The first set consists of approximately 10 nm thick samples of gallium-doped yttrium-iron garnet on gadolinium gallium garnet (Gd3Ga5O12) (GGG) substrates with different crys- tallographic orientations and different annealing temperatures. The second group con- tains gallium-bismuth-doped neodymium-iron garnet on GGG substrates. These samples have different thicknesses, the concentration of individual elements and different annealing temperatures. All samples were prepared by the metal-organic decomposition method. The analysis of their physical properties was done by magneto-optical Kerr effect (MOKE) and optical experiments. Specifically, MOKE spectroscopy, Faraday hystere- sis loops measurements and spectroscopic ellipsometry. Obtained experimental results were further used to deduce the spectral dependence of complete permittivity tensor. Its spectral dependence was than discussed with relation to the electronic structure of in- vestigated materials which helped to select the best deposition conditions and substrate orientation. 1

For developing commercially utilized high-performance high-temperature superconductors, the fabrication of biaxially textured (RE)Ba₂Cu₃O₇₋ₓ (REBCO, RE ═ Y, Gd) coated conductors via metal–organic decomposition of trifluoroacetate precursors (TFA-MOD) has become an interesting strategy for industrial scale-up due to low costs and simple operation. However, the hygroscopic nature of commonly used precursor solutions makes them very sensitive to water pollution through air humidity. This can lead to a degradation of the final microstructure, which in return deteriorates critical current densities. Here, we present a new method to overcome that problem by using a moderator of 2,4-pentanedione (acac) in a pre-existing REBCO precursor solution. Our results show that even initially low-performance solutions can be enhanced to such an extent that they finally outperform standard high-performance solutions and the temperature window for their optimal growth widens significantly. Scanning electron microscopy gives evidence of considerable microstructural improvements, e.g. avoidance of pore formation and grooves, reduction of buckling and surface granularity. X-ray investigations indicate texture improvements, and electrical measurements reveal that transport critical current densities (Jc) increase in self-field and applied magnetic fields. For YBCO, a molar ratio of acac/RE ═ 0.64 is most effective and leads to an increase of the maximum pinning force density Fmaxp from 1.0 to 2.4 GN mˉ³ at 77 K. For GdBCO, a broad window of annealing temperatures (790–840°C) is possible for films with Jc values above 2.9 MA cmˉ² and Fmaxp above 3 GN mˉ³ at 77 K.