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Substrátem kontrolované fyzikální vlastnosti tenkých vrstev magnetických oxidů pro spintronické aplikace
Maleček, Tomáš ; Veis, Martin (advisor) ; Václavková, Diana (referee)
As conventional electronics approaches its fundamental limits, new paradigms are re- quired. Integration of new spintronic materials with current silicon technology shows great promise. This thesis demonstrates the possibility of growing textured stress-free La2/3Sr1/3MnO3 (LSMO) thin films on silicon with properties comparable to epitaxi- ally grown layers on SrTiO3 (STO). Growth of LSMO is achieved by a two-dimensional nanosheet (NS) seed layer of Ca2Nb3O10 inducing epitaxial stabilization of LSMO films. Samples of LSMO on NS/Si, prepared by pulsed laser deposition, have been shown to have lower magnetization than samples of LSMO on STO yet also possess a higher Curie temperature by more than 10 K. Spectral dependence of the full permittivity tensor was calculated from optical and magneto-optical measurements. Spectra of the off-diagonal element have been fitted with three diamagnetic transitions located around 1.9, 2.9 and 3.5 eV for samples on NS/Si as well as for samples on STO. Similarities between the samples open the possibility of integration of LSMO into silicon technology using NS. Temperature-dependent optical and magneto-optical properties of a sample of LSMO on STO have been evaluated.
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Magneto-optical properties of ferrimagnetic garnet thin films with perpendicular magnetic anisotropy
Šetina, Jan ; Veis, Martin (advisor) ; Zázvorka, Jakub (referee)
The aim of this bachelor thesis is to optically and magnetooptically characterize terbium iron garnet and determine its compensation temperature. Another goal is to study magnetooptical response of bismuth doped iron garnets. This analysis was done by magnetooptical spectroscopy, which is suitable for study of thin films due to its high sensitivity and contactlessness. The experimental setup, which allows temperature dependent magnetooptical measurements, was developed and used in the thesis. The spectra of optical constants were deduced using spectroscopic ellipsometer. Hysteresis loop and Faraday rotation was measured on selected sample. These measurements provided new interesting insights in the materials properties, which are discussed in this thesis. 1
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Relativistic spintronic effects in semiconductor structures
Nádvorník, Lukáš ; Jungwirth, Tomáš (advisor) ; Ramsay, Andrew (referee) ; Veis, Martin (referee)
The spin transport and dynamics of optically injected spin polarized carri- ers are studied with a high spatial and/or time resolution in semiconductor GaAs-based heterostructures in multiple transport regimes. An unexpectedly long-scale and high-speed spin diffusion transport is observed in a long-lived electron sub-system induced optically at an undoped single GaAs/AlGaAs heterointerface. A diffusion and drift-dominated spin transport is investi- gated using an electrical spin-detection via the inverse spin Hall effect in doped GaAs-based systems at room and low temperatures. It is shown that the inverse spin Hall signal and the spin transport parameters can be con- trolled by a direct application of an electric field or by expanding a depleted zone of a planar pn-junction.
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Studium fyzikálních vlastostí magnetických oxidů spektroskopickými metodami
Zahradník, Martin ; Veis, Martin (advisor) ; Kouřil, Karel (referee)
Two groups of magnetic oxides were investigated in this thesis. Thin films of La2/3Sr1/3MnO3 (LSMO) deposited by pulsed laser deposition (PLD) on SrTiO3 (STO) substrates were characterized by polar and longitudinal magneto-optical (MO) Kerr spectroscopy. Experimental results were compared to theoretical calculations based on the transfer matrix formalism. A very good agreement between experimental and theoretical data revealed high magnetic ordering down to 5 nm of film thickness as well as a mechanism of suppression of double exchange interaction near the LSMO/STO interface. Magnetically doped Ce1-xCoxO2-δ films deposited by PLD on MgO (x = 0.05 and 0.10) and oxidized Si (x = 0.20) substrates were studied by combination of spectroscopic ellipsometry and MO Faraday and Kerr spectroscopy. Both diagonal and off-diagonal permittivity tensor components were obtained and verified by theoretical calculations confronted with experimental data. Diagonal spectra revealed two optical transitions from oxygen to cerium states. Off-diagonal spectra revealed two paramagnetic transitions involving cobalt ions. An essential influence of cobalt doping on the resulting ferromagnetic properties of CeO2 was observed.
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5f-electron Magnetism in Intermetallic Uranium Compounds
Vališka, Michal ; Sechovský, Vladimír (advisor) ; Šob, Mojmír (referee) ; Veis, Martin (referee)
Tato práce je zaměřená na studium magnetických vlastností tří r·zných sloučenin na bázi uranu obsahujících 5f elektrony (U4Ru7Ge6, UAu2Si2 a UIrGe). V rámci této práce byly, za pomoci r·zných metod, připraveny vysoce kvalitní krystaly těchto sloučenin. Vlastnosti těchto systém· byly studovány r·znými objemovými meto- dami (magnetizace, měrné teplo, teplotní roztažnost, elektrický transport) a také neu- tronovým a rentgenovým rozptylem při širokém spektru vnějších podmínek (nízká teplota, vysoké magnetické pole, vysoký tlak). Kombinace těchto metod odhalila komplexní chování těchto systém· a pomohla sestrojit jejich magnetické fázové diagramy. První studovanou sloučeninou je feromagnet U4Ru7Ge6vykazující velmi nízkou mag- netokrystalovou anizotropii, která je neočekávaná pro sloučeninu na bázi uranu. To se promítá do izotropní závislosti téměř všech měřených fyzikálních vlastností. Bylo zjištěno, že osa snadné magnetizace se mění v uspořádaném stavu a tento jev je spojen s anomáliemi v teplotní roztažnosti ukazující na možnou rhomboedrickou distorzi. Ta vede k vytvoření dvou odlišných pozic uranu s odlišným magnetickým momentem. Tato před- pově¤ byla potvrzena teoretickými výpočty a pomocí polarizované neutronové difrakce. Rozdíl magnetických moment· na dvou odlišných uranových pozicích je zp·soben...
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Study of physical properties of nanostructures using magneto-optical techniques
Beran, Lukáš ; Veis, Martin (advisor) ; Mistrík, Jan (referee)
Magneto-optical spectroscopy methods are used to study magnetic pro- perties of materials down to nanometer dimensions due to its high sensiti- vity and non-contact nature. This requires sophisticated experimental setup, advanced technical equipment and precise optical components arrangement. This thesis describes the basic physical principles of magneto-optical Kerr spectroscopy. On the basis of these principles is designed and developed a new, much simpler experimental setup with crossed polarizers. This arran- gement has the same order of sensitivity and accuracy of measurement as commonly used modulation techniques to which it is compared in this work. Finally, this arrangement is applied to the study magneto-optical properties of selected magnetic structures and these properties are discussed. 1
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Light propagation in magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor) ; Veis, Martin (referee)
Transparent magnetic materials, among the others semiconductors, have recently come to the focus of interest in both basic and applied research because they have great potential in optical applications and they can be used in optical spectroscopy to investigate fundamental physical phenomena. The theoretical calculations introduce that these materials have some extraordinary properties like asymmetric reflectance when light impact the sample from the opposite angles. In this bachelor thesis, transfer matrix formalism is derived based on Maxwell equations, taking into account special form of effective permittivity. The reflection coefficient for one layer demonstrates, that the asymmetric reflectance appears for transversal- magnetic polarization of light and transversal magnetization in the studied material. The derived formulae are used to calculate the difference in reflectivities for the waves impacting the structure from opposite angles. Ga1−xMnxAs with different concentrations of manganese is assumed to be the essential transparent magnetic layer in the sample. 1
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Vliv pnutí na magnetooptické vlasnosti La2/3Sr1/3MnO3
Maleček, Tomáš ; Veis, Martin (advisor) ; Verhagen, Timotheus Guillaume Albertus (referee)
The influence of epitaxial strain on La2/3Sr1/3MnO3 (LSMO) thin films has been studied by magneto-optical spectroscopy. The investigated samples have been grown by pulsed laser deposition on four different substrates with varying degree of compressive and tensile strain. The spectra of the magneto-optical Kerr effect (MOKE) have been measured. Deterioration of magnetic properties with increasing epitaxial strain has been observed. The off-diagonal elements of the permittivity tensor, numerically calculated from the MOKE and spectroscopic ellipsometry measurements, confirmed two already reported electronic transitions. A third transition at around 4.3 eV has been observed on samples grown under compressive strain. The dependence of the Kerr rotation spectra on temperature has been measured for all four samples. The Curie temperatures have been estimated for all samples with the exception of LSMO grown on LaAlO3 which undergoes a spin reorientation transition at 200 K. The low temperature measurements on the compressively strained samples showed amplification of the third transition supporting the claim of it being paramagnetic. Also observed was a change in the spectra of the Kerr rotation of the sample grown on SrTiO3 which undergoes a structural transition at 105 K, and, therefore, changes the epitaxial strain.
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