Národní úložiště šedé literatury Nalezeno 9 záznamů.  Hledání trvalo 0.00 vteřin. 
Magneto-optical gradient effect imaging of magnetic textures
Molnár, Tomáš ; Hamrle, Jaroslav (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Foundations of magneto-optics (MO), the field studying the influence of magnetic fields and magnetization on the propagation of light within matter, had been laid over a century and a half ago. Since then, MO has become one of the most widely used methods for magnetic imaging at the micro-scale. In addition to the MO Faraday and Kerr effects, which are linear in magnetization, effects quadratic in magnetization (Voigt or Cotton-Mouton effect) or dependent on magnetization-gradients (gradient effect) were later found. In particular, the MO gradient effect was the last to be discovered, but as it only decorated magnetic domain boundaries, it has not attracted so far the same interest as the Kerr effect for magnetic imaging. This work investigates the usefulness of the magneto-optical gradient effect to characterize nanoscale spin configurations, such as domain walls in perpendicularly magnetized materials. We present a novel experimental approach to reveal the properties of the MO gradient effect by exploiting its symmetries with respect to the polarization of light. Further, we analytically express the corresponding signal using an available theoretical model. By comparing simulated MO gradient effect signals obtained from the transfer matrix method and experimentally retrieved signals, we explore the possibility of characterizing the internal spin structure of nanoscale magnetic domain walls.
Optical study of laser-induced magnetic phase transitions
Velič, Alexander ; Ligmajer, Filip (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
To perform ultrafast storage of data based on magnetic materials, a new way of sub-picosecond magnetization is researched. Iron-Rhodium is suggested as convenient material which is capable of performing laser induced magnetization. Preparations for this experiment consists of sample growth using physical vapor deposition method of magnetron sputtering and subsequent sample characterization. Three samples were prepared, each with different concept of temperature tuning. Sample I is tuned via composition alteration ( $Fe_{1-x}Rh_x$ ). Sample II deposition onto a sapphire substrate induced tensile in-plane stress. By carbon doping Iron-Rhodium thin film of sample III. The thin film samples are characterized by using vibrating sample magnetometry and optical microscopy. Vibrating sample magnetometry granted a way of recording field driven and more importantly thermally driven hysteresis curves. Measurements yielded precise values of phase transition temperatures for antiferromagnetic-to-ferromagnetic and ferromagnetic-to-antiferromagnetic were detetermined for samples I, II, and III to be 325.9 K and 306 K, 321 K and 291 K, and 311.8 K and 288 K, respectively. Characteristic values of magnetization saturation, coercive field, residual magnetization and temperature difference between phase transition temperatures were recorded. Custom code in combination with microscopy images offered an insightful information on surface region specific domain growth. Combining results of both methods granted a deeper understanding of ''how'' and ''when'' aforementioned magnetostructural phase transition takes affect. The ultrashort laser induced magnetization utilizes a custom laser set-up. The observation of irradiated Iron-Rhodium thin film using optical microscopy shows stable ferromagnetic domains in a laser path pattern. Thus concluding that Iron-Rhodium thin films are prepared, characterized by magnetometry as a function of temperature, and the ultrafast laser induced magnetization was successfully performed.
Ultrafast laser-induced control of magnetic materials
Opršal, Jakub ; Wojewoda, Ondřej (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Magnetic materials are widely used for digital data storage. Data are written in form of bits using external magnetic field. It was long thought that magnetic materials could not be controlled faster than 10-100 ps. A breakthrough experiment in 1996 paved the way for a new field, showing that light can also controlled with femtosecond laser pulses and in the order of picoseconds. Here, we replicate fundamental laser-induced all-optical switching experiments in ferromagnetic and ferrimagnetic materials. Ultrafast laser setup was developed to perform such experiments with different light polarization. Thanks to this, we can distinguish different mechanism and different phenomena present for ultrafast control of magnetic materials.
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.
Development of the scanning time-resolved Kerr microscope
Nekula, Zdeněk ; Arregi Uribeetxebarria, Jon Ander (oponent) ; Wojewoda, Ondřej (vedoucí práce)
In recent days, magnetic materials, structures, and devices are getting more popular, especially those related to spintronics. Research and development of such magnetic samples require a way to observe magnetization with good spatial and temporal resolution. Most dynamic changes of magnetization are realized in nanoseconds or even faster. If we can detect these dynamic processes, we can reveal many exciting magnetization features and add the fourth dimension to our experiments. We introduce a scanning Kerr microscope working in two modes: static and dynamic. In static mode, our microscope detects a direction of magnetization in a variable magnetic field. In dynamic mode, we use a pump-probe method to reach a temporal resolution and observe a fast evolution of magnetization.
Magnetic properties of self-assembled FeRh nanomagnets
Motyčková, Lucie ; Fruchart, Olivier (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Magnetic nanoparticles and nanostructured materials are of great promise in many domains, including biomedicine, environmental remediation, or energy harvesting. Therefore, there is an ever-growing interest in their unique nanoscale functionalities as well as in the development of viable fabrication routes. This thesis investigates a self-assembly route, specifically solid-state dewetting of thin films, to produce epitaxial nanoisland arrays of the FeRh alloy on different single-crystal substrates. It is shown that using this fabrication route, the metamagnetic phase transition is preserved in nanoscale confined geometries. The morphology and magnetic properties of the self-assembled FeRh nanomagnets are characterized by a combination of experimental techniques and modeling, finding that their equilibrium shapes and magnetic order are closely interconnected. Furthermore, a route for obtaining free-standing nanoparticles is devised, which could potentially allow using metamagnetic nano-objects in cell cultures and biomedicine in general. To do so, the supported FeRh nanomagnets are released from the substrate via chemical wet etching. The behavior of the nanoparticles and their response to temperature cycling and magnetic field is subsequently studied in a liquid environment. The metamagnetic properties of separated nanoparticles are characterized using vibrating sample magnetometry.
Magneto-optical investigation of spintronic materials
Vojáček, Libor ; Flajšman, Lukáš (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
The magneto-optical Kerr effect is a useful tool for accessing the magnetic properties of metallic surfaces. The magnetization reversal process controlled by an external applied field and magneto-optically measured can give us information about the anisotropic properties of magnetic systems. In the presented work, we review the theoretical aspects of magnetization reversal and the changes of light polarization upon reflection from a magnetized medium. Description of a functional, high-sensitivity magneto-optical setup based on the polarization modulation technique is given. The apparatus was assembled by modifying an already existing similar setup. Measurements on thin-film magnetic layers prove its functionality and reveal the properties of metamagnetic thin films from FeRh, which is a material with potential applications in spintronics.
Evaluation of Different Dielectrics For Mid-Infrared Waveguides
Konečný, Aleš ; Arregi Uribeetxebarria, Jon Ander (oponent) ; Detz, Hermann (vedoucí práce)
The utilization of plasmon polariton waveguides for mid-infrared light has proven its suitability for sensor applications. The waveguide can be surrounded by a gaseous or liquid phase medium, which contains an analyte substance of which the concentration can be measured. The electromagnetic field propagates along the waveguide, which has to satisfy low losses and sufficient interaction conditions. These are fulfilled using a thin dielectric layer applied on a metal surface. This thesis is focused on Si-based dielectrics. Within this work, multilayer waveguides were fabricated by high vacuum magnetron sputtering, plasma-enhanced vapor deposition and photolithography. The deposition was carried out on commonly used Si substrates and is ready to be transfered to InP-based chips. Evaluation of dielectric layers and fabrication methods are based on ellipsometric measurements of refractive index and extinction coefficient in the infrared spectrum.
Epitaxial growth and characterization of metamagnetic nanoparticles for biomedical applications
Motyčková, Lucie ; Gröger,, Roman (oponent) ; Arregi Uribeetxebarria, Jon Ander (vedoucí práce)
Magnetic nanoparticles represent a promising platform for a vast number of biomedical applications in continuously developing domains of diagnostics and therapeutics. Novel magnetic nanoscale technologies based on metamagnetic materials may provide significant benefits, for instance, in terms of easily controllable actions on biological species in the human body. This thesis investigates the growth mechanisms and magnetic properties of supported nanoparticles made of the iron-rhodium (FeRh) alloy on the MgO substrate. The FeRh compound was chosen for its specific transition from the antiferromagnetic to ferromagnetic phase occurring slightly above room temperature, thus allowing the control of magnetic properties of nanoparticles in the temperature range close to the human body. The presented nanostructures have been fabricated via magnetron sputtering using the bottom up preparation approach. The morphology and magnetic behavior of such deposited nanostructures have been investigated via atomic and magnetic force microscopy, which provide spatially resolved antiferromagnetic and ferromagnetic domain structure in the individual nanoislands.

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