A sanitização de dados é um dos desafios que está em aberto quando tange a segurança de dados nos discos rígidos. Há duas formas de realizar este procedimento de sanitização de dados nos discos rígidos. A primeira é a utilização de técnicas físicas que visam à destruição do disco rígido por completo. A segunda é a utilização de técnicas lógicas que visam realizar a sanitização dos dados armazenados no disco, permitindo que este seja reutilizado. A proposta principal deste trabalho é a de verificar por meio da técnica de Microscopia de Força Magnética (MFM) a possibilidade de recuperação dos dados originais após o processo de sanitização ter ocorrido por meio de uma técnica lógica. Com este objetivo foram selecionadas oito técnicas lógicas (Gutmann, VSITR, RCMP TSSIP OPS-II, CSEC ITSG-06, DoD 5220.22-M, AR 280-19, GOST R 50739-95 e ISM 6.9.92), após esta seleção foi realizada uma avaliação lógica dessas técnicas com o intuito de selecionar duas técnicas para a avaliação experimental. Para realizar a avaliação experimental foram utilizados dois microscópios (Dimension Icon e o MultiMode 8) para aplicar a técnica de MFM em disco rígido. O objetivo foi comprovar a eficiência das técnicas lógicas na sanitização de dados armazenados nos discos rígidos. / Data sanitization is one of the challenges you face when it comes to data security on hard disk. There are two ways to perform this data sanitization procedure on hard disks. The first one is the deployment of physical techniques aimed at destroying the hard drive altogether. The second one is the use of logical techniques that aim to sanitize the data stored on the disk, allowing it to be used again. The main purpose of this work is to verify through the Magnetic Force Microscopy technique (MFM) the possibility of recovering of the original data after the sanitization process has occurred through of a logical technique. To this purpose, eight logics (Gutmann, VSITR, RCMP TSSIP OPS-II, CSEC ITSG-06, DoD 5220.22-M, AR 280-19, GOST R 50739-95 and ISM 6.9.92) were selected. After this selection, a logical evaluation of these techniques was carried out for selecting two techniques for the experimental evaluation. To perform the experimental evaluation, two microscopes (Dimension Icon and MultiMode 8) were used to apply the MFM technique to the hard disk. The objective was to verify the efficiency of the logical techniques in the sanitization of data stored in the hard disks.

In der vorliegenden Arbeit wurden die mikromagnetische Struktur sowie das Ummagnetisierungsverhalten epitaktisch gewachsener MnAs Filme auf dem Substrat GaAs untersucht. Im Mittelpunkt steht die mikromagnetischen Struktur von anisotrop erspannten MnAs Filmen auf GaAs(001). Die Verspannung führt zur selbstorganisierten Anordnung ferromagnetischer Streifen. Ihre Domänenstruktur wurde mittels MFM (magnetischer Kraftmikroskopie) bestimmt und mit den Resultaten der XMCDPEEM (X-ray magnetic circular dichroism photoemission electron microscopy) verglichen. Um eine vollständige Charakterisierung der mikromagnetischen Eigenschaften der Streifenstruktur zu erreichen, wurden die MFM Experimente in einem äusseren Magnetfeld durchgeführt. Die Beantwortung der zentralen Frage nach der Domänenstruktur ist mit der Entwicklung eines mikromagnetischen Simulators für dreidimensionale magnetische Strukturen auf mesoskopischer Skala gelungen. Die Stabilität der dreidimensionalen mikromagnetischen Struktur hängt von den Eigenschaften der selbstorganisierten Streifenstruktur ab, d.h. sowohl von der Filmdicke als auch vom Verhältnis ihrer Breite zur Filmdicke - und damit der Temperatur. Durch die Erkenntnis, dass eine magnetische Struktur in der Tiefe des Streifens vorhanden ist, können die verbleibenden Unterschiede in den XMCDPEEM- und MFM-Resultaten erklärt werden. Durch die Simulationsergebnisse in Kombination mit den Experimenten wird eine widerspruchsfreie Deutung der mikromagnetischen Struktur sowie deren Ummagnetisierungsverhalten ermöglicht. Zudem wird die mikromagnetische Struktur von MnAs auf GaAs(111) simuliert und damit das Verständnis der mikromagnetischen Strukturen auf alle vorhandenen Substratorientierungen vervollständigt. / In the present thesis the micromagnetic structure, as well as the magnetization reversal, of epitaxial MnAs films on GaAs substrates are studied. The investigation is focused on the micromagnetic structure of anisotropically strained MnAs films on GaAs(001). The strain originates a selforganized array of ferromagnetic stripes. The magnetic domains were investigated using MFM (magnetic force microscopy) and the results were compared with XMCDPEEM (X-ray magnetic circular dichroism photoemission electron microscopy). To completely characterize the micromagnetic properties of the stripe structure, MFM experiments were performed in the presence of an external field. To unambiguously determine the domain structure a three-dimensional micromagnetic simulator was developed capable to calculate magnetic structures with mesoscopic dimensions. The stability of the three-dimensional micromagnetic structure depends on the properties of the selforganized stripe structure, i.e., on the film thickness as well as on the ratio of the stipe width to thickness - and thus the temperature. Taking into account the magnetization distribution in-depth, the remaining differences between the XMCDPEEM and the MFM results can be explained by the disturbing effect of the MFM tip. The results of the micromagnetic simulations, in combination with the experimental results, allow for a determination of the micromagnetic structure in an applied field throughout the phase coexistence regime. Moreover, the micromagnetic structure of MnAs films on GaAs(111) is simulated and thus the understanding of the micromagnetic properties have been extended on all substrate orientations.

In the current study, we give a report when oxalic acid was used as an electrolyte to synthesize an AAO template with hexagonal pore array. Optimum parameters were observed as 0.4 M of oxalic acid, anodizing voltage of 45 V, temperature of approximately 8 °C and the period of 120 minutes. Atomic force microscope (AFM) and High resolution scanning electron microscope (HRSEM) showed that template has an average pore diameter of 103 nm. Co and MnOx (x = 1,2) nanostructures were selectively deposited in the pores of the template using a novel atomic layer deposition (ALD) technique. The diameter sizes and the array of the nanostructures and the template were corresponding. Energy dispersive xrays (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co and MnOx (x =1,2) on the samples while x-ray diffraction (XRD) provided an indication of their orientations. Magnetic force microscopy as main characterization tool showed the existence of multi-domains on both Co and MnOx (x =1,2) nanostructures.

Local studies of magnetic flux line (vortex) distribution in superconducting thin films and their pinning by natural and artificial defects have been performed using low-temperature magnetic force microscopy (LT-MFM). Taken a 100 nm thin NbN film as an example, the depinning of vortices from natural defects under the influence of the force that the MFM tip exerts on the individual vortex was visualized and the local pinning force was estimated. The good agreement of these results with global transport measurements demonstrates that MFM is a powerful and reliable method to probe the local variation of the pinning landscape. Furthermore, it was demonstrated that the presence of an ordered array of 1-μm-sized ferromagnetic permalloy dots being in a magneticvortex state underneath the Nb film significantly influences the natural pinning landscape of the superconductor leading to commensurate pinning effects. This strong pinning exceeds the repulsive interaction between the superconducting vortices and allows vortex clusters to be located at each dot. Additionally, for industrially applicable YBa$_2$Cu$_3$O$_{7-\delta} thin films the main question discussed was the possibility of a direct correlation between vortices and artificial defects as well as vortex imaging on rough as-prepared thin films. Since the surface roughness (droplets, precipitates) causes a severe problem to the scanning MFM tip, a nanoscale wedge polishing technique that allows to overcome this problem was developed. Mounting the sample under a defined small angle results in a smooth surface and a monotonic thickness reduction of the film along the length of the sample. It provides a continuous insight from the film surface down to the substrate with surface sensitive scanning techniques.

In the current study, we give a report when oxalic acid was used as an electrolyte to synthesize an AAO template with hexagonal pore array. Optimum parameters were observed as 0.4 M of oxalic acid, anodizing voltage of 45 V, temperature of approximately 8 °C and the period of 120 minutes. Atomic force microscope (AFM) and High resolution scanning electron microscope (HRSEM) showed that template has an average pore diameter of 103 nm. Co and MnOx (x = 1,2) nanostructures were selectively deposited in the pores of the template using a novel atomic layer deposition (ALD) technique. The diameter sizes and the array of the nanostructures and the template were corresponding. Energy dispersive xrays (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co and MnOx (x =1,2) on the samples while x-ray diffraction (XRD) provided an indication of their orientations. Magnetic force microscopy as main characterization tool showed the existence of multi-domains on both Co and MnOx (x =1,2) nanostructures.

Sistemas ultrassônicos tiveram uma evolução tecnológica nos últimos anos e isso permitiu que seus recursos de hardware e software pudessem ser explorados para extrair informações, auxiliando em diagnósticos e tratamentos mais eficazes. Através da análise do comportamento mecânico de tecidos moles, técnicas como elastografia estática, vibroacustografia, elastografia transiente e elastografia remota tiveram seu papel reconhecido na complementação do diagnóstico clínico. Contudo, a propagação destas técnicas na medicina tem sido restringida pela acessibilidade às tecnologias utilizadas, ausências de parâmetros quantitativos, dificuldade da excitação em estruturas profundas e acesso a informações em níveis moleculares. Este estudo aborda o desenvolvimento de um protocolo para efetuar medidas quantitativas de viscoelasticidade em tecidos moles marcados com nanopartículas de óxido de ferro usando excitação magnética e medição ultrassônica. Ao aplicar uma força magnética pulsada em um meio fluido marcado com nanopartículas magnéticas, um movimento é induzido, gerando uma onda de cisalhamento que se propaga pelo tecido. A propagação dessa onda é mapeada usando a técnica de ultrassom pulso-eco e processamento de dados usando métricas de similaridades entre ecos (mapa de rf) consecutivos. Nos estudos realizados em mimetizadores de tecidos moles (phantom) com características mecânicas equivalentes ao tecido biológico, a amplitude de deslocamento dessas ondas é da ordem de micrometro. Através da medida da velocidade deslocamento dessa onda avaliou-se o melhor modelo reológico para quantificar os parâmetros mecânicos de viscosidade e elasticidade. Os resultados mostraram a eficiência desta técnica ao quantificar os valores viscoelásticos condizentes com a literatura e a comprovação da análise de tecidos moles marcado com nanopartículas excitadas com campo magnético de baixa intensidade, possibilitando uma avaliação em âmbito molecular em tecidos moles. / Ultrasonic systems had a technological development in recent years and allowed their hardware and software resources could be exploited to extract information, assisting in more effective diagnosis and treatment. Through the mechanical behavior analysis of soft tissue techniques such as static elastography, vibroacoustography, transient elastography and remote elastography had recognized role in complementing clinical diagnosis. However, the spread of these techniques in medicine has been restricted by accessibility to the technologies used, quantitative parameters absences, difficulty of deep structures access and information on molecular levels. This study addresses the development of a protocol to make quantitative measurements of viscoelastic soft tissue labeled with iron oxide nanoparticles using magnetic excitation and ultrasonic measurement. By applying a pulsed magnetic force in a fluid medium labeled with magnetic nanoparticles, a motion is induced, generating a shear wave that propagates through the tissue. The propagation of this wave is mapped using the pulse-echo ultrasound technique and data processing using similarities measurements between echoes (rf map) consecutive. In studies of soft tissue-mimicking phantom with mechanical properties equivalent to the biological tissue, the displacement amplitude of these waves is of micrometer order. By measuring the shear wave velocity, it was evaluated the best rheological model for quantifying mechanical parameters of viscosity and elasticity. The results showed the efficiency of this technique to quantify the viscoelastic values consistent with the literature and the evidence of soft tissue analysis labeled excited nanoparticles with low intensity magnetic field, providing an assessment on the molecular level in soft tissues.

>Magister Scientiae - MSc / In the current study, we give a report when oxalic acid was used as an electrolyte to synthesize an AAO template with hexagonal pore array. Optimum parameters were observed as 0.4 M of oxalic acid, anodizing voltage of 45 V, temperature of approximately 8 °C and the period of 120 minutes. Atomic force microscope (AFM) and High resolution scanning electron microscope (HRSEM) showed that template has an average pore diameter of 103 nm. Co and MnOx (x = 1,2) nanostructures were selectively deposited in the pores of the template using a novel atomic layer deposition (ALD) technique. The diameter sizes and the array of the nanostructures and the template were corresponding. Energy dispersive xrays (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co and MnOx (x =1,2) on the samples while x-ray diffraction (XRD) provided an indication of their orientations. Magnetic force microscopy as main characterization tool showed the existence of multi-domains on both Co and MnOx (x =1,2) nanostructures. / South Africa

The thesis deals with magnetic force microscopy of soft magnetic nanostructures, mainly NiFe nanowires and thin-film elements such as discs. The thesis covers almost all aspects related to this technique - i.e. from preparation of magnetic probes and magnetic nanowires, through the measurement itself to micromagnetic simulations of the investigated samples. We observed the cores of magnetic vortices, tiny objects, both with commercial and our home-coated probes. Even domain walls in nanowires 50 nm in diameter were captured with this technique. We prepared functional probes with various magnetic coatings: hard magnetic Co, CoCr and soft NiFe. Hard probes give better signal, whereas the soft ones are more suitable for the measurement of soft magnetic structures as they do not influence significantly the imaged sample. Our probes are at least comparable with the standard commercial probes. The simulations are in most cases in a good agreement with the measurement and the theory. Further, we present our preliminary results of the probe-sample interaction modelling, which can be exploited for the simulation of magnetic force microscopy image even in the case of probe induced perturbations of the sample.

This dissertation thesis deals with the computational modelling of the dynamic response of the rotating electrical machine structure on the application of the magnetic forces. Apart from the dynamic response of the ideal symmetrical machine, the influence of the air gap eccentricity on the dynamics response is studied in this work. A basic type of the air gap eccentricity, which is caused by eccentric mounting of the rotor pack on the shaft of the rotor, is considered. The calculations the dependence of the magnetic forces on the time and a misalignment of the rotor pack are performed as first. The computational model of the magnetic field of the rotating electrical machine, which is based on solution of the electromagnetic coupled field analysis by finite element method, is used for this purpose. An analysis of the influence of the unbalanced magnetic pull and the stiffness of some parts of the machine on the modal properties of the machine is performed in the second part of this thesis. A third part of this thesis is focused on the calculation of the dynamic response of the machine during the steady state operation of the machine and the influence of the rotor pack misalignment on the dynamic response is studied. The obtained results showed that the tangential components of the magnetic forces, which act on the stator pack, excite significant torsional vibration of the stator. Besides the vibration of the stator of the machine, the influence of the rotor pack misalignment on the sound power of the machine, vibration of the rotor, loads of rotor bearings and air gap eccentricity is studied in this thesis.

Local studies of magnetic flux line (vortex) distribution in superconducting thin films and their pinning by natural and artificial defects have been performed using low-temperature magnetic force microscopy (LT-MFM). Taken a 100 nm thin NbN film as an example, the depinning of vortices from natural defects under the influence of the force that the MFM tip exerts on the individual vortex was visualized and the local pinning force was estimated. The good agreement of these results with global transport measurements demonstrates that MFM is a powerful and reliable method to probe the local variation of the pinning landscape. Furthermore, it was demonstrated that the presence of an ordered array of 1-μm-sized ferromagnetic permalloy dots being in a magneticvortex state underneath the Nb film significantly influences the natural pinning landscape of the superconductor leading to commensurate pinning effects. This strong pinning exceeds the repulsive interaction between the superconducting vortices and allows vortex clusters to be located at each dot. Additionally, for industrially applicable YBa$_2$Cu$_3$O$_{7-\delta} thin films the main question discussed was the possibility of a direct correlation between vortices and artificial defects as well as vortex imaging on rough as-prepared thin films. Since the surface roughness (droplets, precipitates) causes a severe problem to the scanning MFM tip, a nanoscale wedge polishing technique that allows to overcome this problem was developed. Mounting the sample under a defined small angle results in a smooth surface and a monotonic thickness reduction of the film along the length of the sample. It provides a continuous insight from the film surface down to the substrate with surface sensitive scanning techniques.