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Electrotransport properties of CuMnAs single crystals
Volný, Jiří ; Uhlířová, Klára (advisor)
Electrical transport measurement of small, irregular shape sample is difficult task. In order to overcome these limitations, this thesis employed a focused ion beam microfabrication. Process of microfabrication is successfully tested on a room temperature antiferromagnet CuMnAs. Temperature dependence resistivity and magnetoresistance of tetragonal bulk CuMnAs single crystal is found to be strongly anisotropic due to layered structure and magnetic order. Anisotropic magnetoresistance shows two fold symmetry and reached a magnitude of 0.12 %. Employing the∼ phenomenological Stoner-Wohlfarth we conclude that the sample has uniaxial magnetic anisotropy with an easy axis not pointing along any principal crystallographic direction and behaves like a two domain antiferromagnet.
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Zpracování průzkumných prací ve zvolené lokalitě jako podklad pro KoPÚ
UHLÍŘOVÁ, Klára
The bachelor thesis on the topic of "Processing of exploratory work in the selected locality, as a basis for the complex land adjustment", is focused on the implementation of exploratory work according to the valid methodology. The field exploration was carried out in the cadastral area Hůrky u Lišova, which is located not far from České Budějovice. The first part is focused on literature research, which explains the basic terms related to land reparcelling with its brief history. The second part is focused on the evaluation of the state of nature and landscape in the cadastral area. The aim of this work was to elaborate the exploratory works in the selected locality according to the valid methodical instructions of land reparcelling.
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Morphology and physical properties of misfit layer compound "VPbS3 "
Tetalová, Kateřina ; Uhlířová, Klára (advisor) ; Kúš, Peter (referee)
The subject of this bachelor thesis is the research on the morphology and physical properties of the misfit layer compound VPbS3. The main part of the work was the study of the sample cleaved surface. We focused on chemical stability, the to- pography of the cleaved surface, the depths of cleaved artefacts and the influence of the structure of the cleaved surface on the exfoliation of the thin layers. We exfoliated the sample to two substrates - Si/SiOx/5 nm Au a Si/300 nm SiOx - to compare adhesion. We also measured the temperature dependence of the electrical resistance of the material VPbS3. Within the work were used and compared three microscope methods - optical microscopy, scanning electron microscopy and atomic force microscopy. Marginally we also focused on the growth of the crystals VPbS3 and verified their composition. From the perspective of the AFM, the sample VPbS3 is chemically stable. We managed to exfoliate a layer with a thickness of 1,9 nm to the Si/300 nm SiOx substrate and with a thickness of 0,8 nm to the Si/SiOx/5 nm Au substrate. Following the previous measurement, the electric resistivity measu- rement reports semiconducting behaviour. 1
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Kontrola magnetické anizotropie v multivrstvách Pt/Co/Pt
Nowak, Lukáš ; Veis, Martin (advisor) ; Uhlířová, Klára (referee)
This thesis aims to explore the effect of in situ ion gun etching on magnetic proper- ties, such as perpendicular magnetic anisotropy, of Pt/Co/Pt multilayers. Perpendicular magnetic anisotropy is of interest due to its importance in spintronic application. Calibration spectroscopic ellipsometry measurements of Pt and Co layers to obtain sputter yields of respective magnetron targets were performed as a first step. After that, ten Pt/Co/Pt multilayers with different Co and top Pt layer thicknesses were prepared. Five of these samples were etched by the ion gun, mounted inside of the magnetron chamber, during different stages of the deposition. To characterize the prepared samples, experimental and modeled Kerr rotation spectra were confronted. This provided an insight into the cross-sections of the investigated samples. Magnetic hysteresis loops measured by vibrating sample magnetometer and Kerr rotation setup demonstrated higher coercive field and change of the slope of the loop induced by ion etching. When compared to the obtained cross-sections, a correlation between the change of magnetic loops and intermixing of Pt and Co at the interface was visible. This intermixing was higher in samples treated by the ion gun. 1
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Electrotransport properties of CuMnAs single crystals
Volný, Jiří ; Uhlířová, Klára (advisor) ; Zázvorka, Jakub (referee)
Electrical transport measurement of small, irregular shape sample is difficult task. In order to overcome these limitations, this thesis employed a focused ion beam microfabrication. Process of microfabrication is successfully tested on a room temperature antiferromagnet CuMnAs. Temperature dependence resistivity and magnetoresistance of tetragonal bulk CuMnAs single crystal is found to be strongly anisotropic due to layered structure and magnetic order. Anisotropic magnetoresistance shows two fold symmetry and reached a magnitude of 0.12 %. Employing the∼ phenomenological Stoner-Wohlfarth we conclude that the sample has uniaxial magnetic anisotropy with an easy axis not pointing along any principal crystallographic direction and behaves like a two domain antiferromagnet.
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Magnetic shape memory alloys: Effects of doping with Cu and Fe
Kancko, Andrej ; Colman, Ross Harvey (advisor) ; Uhlířová, Klára (referee)
In this thesis, the focus is set on studying the properties of Ni-Mn-Ga magnetic shape memory (MSM) alloys, ferromagnetic Heusler compounds, codoped with Fe and Cu. Codoping Ni-Mn-Ga MSM alloys with Fe and Cu had previously been studied due to a synergy in increasing the martensitic transformation temperature - a key parameter for practical applications of the magnetic shape memory effect. We present the preparation process of five Ni-Mn-Ga-Fe-Cu single crystals using the optical floating zone method, as well as the analysis of their composition, crystal structure and magnetic properties, performed following the growth. The results obtained from our single crystals were finally compared with the data from the previously studied polycrystalline Ni-Mn-Ga-Fe-Cu alloys, showing similar trends in increasing the martensitic transformation temperature, the Curie temperature and the saturation magnetisation.
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Investigation of magnetic structures using Kerr microscopy in various configurations
Papáčková, Anežka Terezie ; Zázvorka, Jakub (advisor) ; Uhlířová, Klára (referee)
The magneto-optical Kerr effect (MOKE) is an optical non-destructive and non- invasive method used to investigate the physical properties of magnetic materials that can be further used in magneto-optical technologies. This thesis aims to describe the prin- ciples of Kerr microscopy and afterwards to describe the design and testing of a MOKE based wide-field microscope. The new feature of this microscope prototype consists of the implementation of the rotating analyser, which allows for obtaining the Kerr rotation of the studied system directly from the captured pictures with the accuracy of several milli- degrees. A high-speed CMOS camera combined with image post-processing techniques, is used to obtain high-resolution images. The configuration and accuracy of the microscope is tested by measuring with different sets of angles of crossing and the number of image accumulations. To demonstrate the setup capabilities in different configurations, we pre- sent exemplary measurements on two selected types of samples. Out-of-plane domains are observed on Pr:YIG, in-plane domains on Co:NiMnGa. 1
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Microstructures fabrication for transport properties measurements of heavy fermion compounds
Volný, Jiří ; Uhlířová, Klára (advisor) ; Prchal, Jiří (referee)
In this thesis, we focus on preparation of micro-devices for resistivity measure- ment of CeCoIn5 using focused ion beam technique. Single crystal samples of ∼ 50 µm length were carved out by focused ion beam and transported on silicon sub- strates with prepared gold structures for electrical resistivity measurement. The samples were conductivily attached to gold contact pads by focused ion beam in- duced platinum deposition. Several steps and techniques were optimized: electron litography, golden pads electrical resitivity measurement and platinum structures electrical resitivity measurement and microstructure transport. Electrical resisti- vity measurement of CeCoIn5 single crystal showed superconductive transition at Tc = 2.27 K and H-T phase diagram was created from measurement in magnetic fields. The result obtained from bulk sample are in agreement with literature. On the other hand measurement of micro-devices showed no superconducting transition, suggesting unsufficient quality of samples. 1
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