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Sledování vlastností materiálů s fázovou přeměnou (PCMs) v čase
Šikutová, Eva ; Doležalová Weissmannová, Helena (oponent) ; Řezáčová, Veronika (vedoucí práce)
Bakalářská práce se zabývá sledováním vlastností materiálů s fázovou přeměnou (PCMs, Phase Change Materials) v čase. Teoretický blok je rozdělen do dvou částí. První část se zaměřuje na popis vlastností těchto materiálů, jejich přípravu a využití v různých průmyslových odvětvích. Druhá část představuje metody pro měření vlastností PCMs vzorků. V experimentální části této práce byly PCMs po známé definované historii analyzovány metodou diferenciální skenovací kalorimetrie (DSC) a získané výsledky byly následně zpracovány a vyhodnoceny.
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Influence of the epitaxial strain at the lateral thin film-stripe interface on the Ferromagnetic-Antiferromagnetic phase coexistence in FeRh
Hrdinová, Sára ; Kepič, Peter (oponent) ; Zadorozhnii, Oleksii (vedoucí práce)
An equiatomic alloy FeRh exhibits a phase transition from antiferromagnetic to ferromagnetic ordering at a temperature about 350 K. This makes it an ideal material for studying exchange interactions between ferromagnetic and antiferromagnetic ordering within a single material system. In this work, we investigate the relaxation of the compressive epitaxial strain caused by nanopatterning of the FeRh film. Relaxation of this strain leads to the stabilization of the ferromagnetic phase, which could lead to the formation of a suitable interface between the relaxed ferromagnetic nanostripe and the compressed antiferromagnetic film. In this bachelor thesis we first describe in detail the magnetic properties of the materials and properties of the FeRh alloy with the emphasis on the phase transformation. Our experiments supported by recent literature research include depositing FeRh layers with thicknesses of 36 nm and 180 nm. After patterning by electron beam lithography, the samples were characterised using Magnetic Force Microscopy. These measurements show that the strain relaxation is strongly dependent on the orientation of the nanostripe with respect to the crystal structure of the substrate. For an orientation of 0°, the strain relaxation is more pronounced than for 45°. The 36 nm thin FeRh layers do not form a continuous phase boundary between the nanostripe and the full film in 1000 nm wide nanostripes. Instead, they form small domains that are indicative of the strain distribution in the structure. Layers of 180 nm thickness show a phase coexistence between the nanopatterned stripe and the film for stripes longer than 25 µm. Well-defined interfaces have been achieved for stripe widths from 1250 nm to 300 nm. For structures with wider stripes, the ferromagnetic phase at the edges of the continuous layer merges with the ferromagnetic phase in the nanostripe, thereby curving the interface. This merging is gradually broken at the interface in the thinner stripe with dimensions 800 nm and 600 nm. The stripe of width 300 nm shows a clear interface between its sides.
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Spatial confinement effects in metamagnetic nanostructures
Jaskowiec, Jiří ; Klapetek, Petr (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
New properties and effects caused by spatial confinement of materials have critical influence in many scientific and technical fields. Reduction of device sizes, increase of recording density and increasing process efficiency are current trends in electronic industry. In this work, the influence of spatial confinement on the metamagnetic phase transition in Iron-Rhodium (FeRh) is studied. The FeRh alloy exhibits a first order phase transition from the antiferromagnetic phase to the ferromagnetic phase. Using magnetic force microscopy in an out-of-plane magnetic field the phase domain structure is imaged and analyzed across the phase transition. Quantitative analysis of measured data is done using the height-height correlation function and its results are compared for different structure sizes and thin layer thicknesses.
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Magnetotransport properties of FeRh nanowires
Fabianová, Kateřina ; Dubroka, Adam (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
Iron-rhodium (FeRh) is a material undergoing a first order magnetic phase transition from antiferromagnetic (AF) to ferromagnetic (FM) phase which occurs when the material is heated above the transition temperature or by applying a sufficiently large magnetic field. This phase transition is accompanied by a significant change in entropy, magnetization and electric resistivity while the transition temperature is strongly dependent on the crystal stoichiometry, elemental substitution, pressure and in case of thin layers on the strain induced by the substrate. This work is focused on the study of magnetotransport properties of wires patterned from FeRh thin layers grown on substrates inducing different strain in the layer. One of the main effects studied in this work is the anisotropic magnetoresistance (AMR) demonstrated by a change of the resistance for different orientations of the magnetic moments in the material with respect to the electric current direction. The AMR was studied both in the FM and AF phase of FeRh. The AMR of the FM phase in the high temperature phase was measured and an unexpected behavior of the AMR of the residual FM phase of FeRh in the low temperature phase was discovered. A strong dependence of the AMR on the orientation of the measured segment with respect to the crystallographic directions of FeRh was explored.
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Effect of ion beam irradiation and annealing on magnetic properties of FeRh nanostructures
Zadorozhnii, Oleksii ; Turčan, Igor (oponent) ; Staňo, Michal (vedoucí práce)
The first order phase transition from antiferromagnetic to ferromagnetic state in Fe50Rh50 at 370 K make it a suitable material for next generation spin electronic devices with a low power consumption. This work deals with the ways how the phase transition temperature of iron-rhodium (FeRh) can be tuned locally in thin films, using focused ion beam (FIB) and thermal annealing. FIB irradiation approach was chosen due to the fact that FeRh displays magnetic sensitivity to the degree of its chemical ordering, which is characteristic to all alloys of ferromagnetic and non-ferromagnetic metals. Thermal annealing enables the relaxation of the structure and restoration of its crystallinity. The magnetic patterns were manufactured using gallium-based FIB and annealed under ultra high vacuum. The topography as well as magnetic behaviour of these ion irradiated patterns were investigated using atomic and magnetic force microscopies at different temperatures, showing a clear dependence between ion irradiation dose and the magnetic response in pre- and post-annealed states.
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Mikroskopie magnetických sil a transportní vlastnosti metamagnetických nanostruktur
Jaskowiec, Jiří ; Vaňatka, Marek (oponent) ; Uhlíř, Vojtěch (vedoucí práce)
Železo-rhodium (FeRh) je látka charakteristická svou fázovou přeměnou prvního druhu mezi antiferomagnetickou (AF) a feromagnetickou (FM) fází. U objemového FeRh je tato změna symetrická vůči směru přechodu. Symetrickou zůstává i při omezení objemového materiálu do tenké vrstvy FeRh. Tato práce se věnuje vlastnostem mezostruktur o laterální velikosti pod jeden mikrometr, ve kterých byla nedávno objevena asymetrie mezi přechodem AF-FM a FM-AF pomocí měření elektrického odporu nanodrátů FeRh v závislosti na teplotě. Pomocí metody mikroskopie magnetických sil v magnetickém poli kolmém na rovinu vzorku je zviditelněna fázová struktura mezostruktur FeRh při fázové přeměně. Kvantitativní analýzou měřeného magnetického signálu je ukázán vliv velikosti struktur na přechlazení FM fáze a skokový nárůst AF fáze při přechodu FM-AF.
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Magneto-optical imaging and analysis of magnetic domain microstructures
Molnár, Tomáš ; Wojewoda, Ondřej (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Magneto-optical effects are associated with the interaction of polarized light with magnetized media. Although discovered nearly two centuries ago, magneto-optics is a widely utilized tool for magnetic characterization due to its high sensitivity and versatility. For example, it enables visualization of magnetic domain structures in microscale magnetic systems via wide-field magneto-optical microscopy. The majority of research on this topic has employed linear effects in magnetization to image domains in ferromagnetic materials, where one measures an optical contrast for regions with opposite magnetization orientations. It has been recently shown that even antiferromagnetic materials can be studied using quadratic magneto-optical effects (Voigt effect), making it possible to visualize regions with different spin axis orientations. In this work, we perform a fundamental magneto-optical microscopy study of magnetic thin film and microstructure systems using linear and quadratic effects. Consequently, the microscale magnetization configuration of continuous and patterned magnetic thin films is interpreted via the image processing strategy developed in this thesis, leading to quantitative vector magnetometry. Moreover, the coexistence of the ferro- and antiferromagnetic phase domains in FeRh films was investigated using optical and magneto-optical microscopy.
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