Made available in DSpace on 2014-10-09T12:33:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:58Z (GMT). No. of bitstreams: 0 / A nanociência e a nanotecnologia vêm abrindo inúmeros desenvolvimentos de dispositivos e sistemas em escala nanométrica, com novas organizações moleculares, propriedades e funções distintas. Nesse contexto, as nanopartículas magnéticas poliméricas são compósitos formados por materiais magnéticos com tamanhos de partículas entre 1 e 100 nm combinados com polímeros funcionais. São materiais bem conhecidos e têm sido amplamente estudados devido às suas aplicações em diversas áreas tecnológicas. Nas áreas biológica e médica, as aplicações incluem separação e imobilização de enzimas e proteínas, melhoria nas técnicas de imagem de ressonância magnética para diagnóstico e sistemas de liberação controlada de fármacos. Neste trabalho, proteínas foram imobilizadas na superfície de um biopolímero combinado com partículas superparamagnéticas de magnetita para formar o compósito magnético. Utilizou-se o biopolímero quitosana, reticulada e funcionalizada com glutaraldeído, aplicável em ensaios biológicos. Obtiveram-se 3 tipos de compósitos magnéticos, os quais foram nomeados QM1Glu, QM2NaGlu e QM3Glu. Foram caracterizados por difratometria de raios X, microscopia eletrônica de varredura, magnetometria de amostra vibrante, calorimetria exploratória diferencial, termogravimetria e espectroscopia por infravermelho. Foram avaliados quanto à imobilização das proteínas albumina de soro bovino (SAB), colágeno e tripsina. A imobilização das proteínas no biopolímero ocorreu em 30 min de incubação. O compósito magnético de quitosana não funcionalizada (QM3) também foi avaliado. Para a tripsina verificou-se que QM3 apresentou maior potencial de imobilização do que QM3Glu. Após 30 dias, QM3-Trip e QM3Glu-Trip ainda apresentavam a tripsina ativada. Foram demonstradas a atividade e a cinética enzimática da QM3Glu-trip com o substrato BApNA. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:43:59Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:05Z (GMT). No. of bitstreams: 1 06656.pdf: 6506694 bytes, checksum: 3c14b01777cb8c5084964ff054604f96 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2016-07-25T10:59:35Z No. of bitstreams: 2 Dissertação - Sara Alves Maciel - 2016.pdf: 11054901 bytes, checksum: 8cddf79cb5700731533eb7125fe234a3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-07-25T11:13:28Z (GMT) No. of bitstreams: 2 Dissertação - Sara Alves Maciel - 2016.pdf: 11054901 bytes, checksum: 8cddf79cb5700731533eb7125fe234a3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-07-25T11:13:28Z (GMT). No. of bitstreams: 2 Dissertação - Sara Alves Maciel - 2016.pdf: 11054901 bytes, checksum: 8cddf79cb5700731533eb7125fe234a3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-04-05 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / In this work, structural, morphological and magnetic properties of cobalt ferrite/zirconium oxide composites prepared via mechanical mixing of the powders were evaluated. Cobalt ferrite powders were obtained by coprecipitation, and some synthesis parameters were optimized, such as the speed of stirring , the concentration of base and metal solutions, in order to obtain stoichiometric ferrites (Fe3+/Co2+ = 2: 1) or near to it. Zirconium oxide powders were synthesized via sol-gel. The composites were analyzed by Atomic Absorption, Field Emission Scanning Electron Microscopy and Spectroscopy Dispersive Energy, Diffraction of X-rays, Infrared Spectroscopy and Vibranting Sample Magnetometry. It was observed the migration of cations between the ferrite and zirconia structures as a result of high diffusion between phases due to heat treatment. The analysis by Field Emission Scanning Electron Microscopy and Spectroscopy Dispersive Energy showed the different microstructures of aggregates present in the composites and the average diameter of the grains. The insertion of a magnetic phase on a non-magnetic matrix caused an increase in the saturation magnetization and the remanent magnetization, and decrease in coercivity as the cobalt ferrite content increases. / Neste trabalho, foram avaliadas propriedades estruturais, morfológicas e magnéticas de compósitos de ferrita de cobalto/óxido de zircônio, preparados via mistura mecânica dos pós. Os pós de ferrita de cobalto foram obtidos pelo método da coprecipitação, tendo seus parâmetros de síntese otimizados, tais como velocidade de agitação, concentração das soluções de base e dos metais, a fim de se obter ferritas estequiométricas (Fe3+/Co2+ = 2:1) ou próximas disso. Os pós de óxido de zircônio foram sintetizados via sol-gel. Os compósitos foram analisados por Absorção Atômica, Microscopia Eletrônica de Varredura com Emissão de Campo e Espectroscopia por Energia Dispersiva, Difratometria de Raios X, Espectroscopia na Região do Infravermelho e por Magnetometria de Amostra Vibrante. Foi observada a migração de cátions entre as estruturas da ferrita e da zircônia como consequência da alta difusão entre as fases devido ao tratamento térmico. A análise por Microscopia Eletrônica de Varredura com Emissão de Campo e Espectroscopia por Energia Dispersiva permitiu verificar as diferentes microestruturas dos agregados presentes nos compósitos e o diâmetro médio dos grãos. A inserção de uma fase magnética em uma matriz não magnética provocou aumento na magnetização de saturação e na magnetização remanescente, além de uma diminuição na coercividade à medida que o teor de ferrita de cobalto aumenta.

Made available in DSpace on 2016-08-18T18:19:25Z (GMT). No. of bitstreams: 1 Carlos Cesar Costa.pdf: 2011505 bytes, checksum: 17efa54b3a1a2bd2009b553d5382bb31 (MD5) Previous issue date: 2008-12-05 / In the present work of dissertation of the master's degree course, we studied the magnetic properties of films simple nanometric's as: iron on oxide of magnesium (F/MgO) and permalloy (Fe Ni) in room temperature, obtained by the eltro-deposition process by sputtering. The experimental results were interpreted in agreement with the models phenomenological that take into account the most relevant terms of the magnetic free energy of the system. We made an approach in accordance with the literature on the main mechanisms that originate the electric resistance in magnetic metallic films, such as: resistance electric ohm's, effects hall, anisotropic magnetoresistance (AMR). it is made a description of the main experimental techniques used in the characterization of films nanometric's, as the Magnetometer Optical for Kerr Effect (MOKE), Ferromagnetic Resonance (FMR) and Magnetoresistance (MR). This last technique, that it uses the method of the four tips, it is used to obtain the magnetoresistance curves. In this work, we studied the effect of the anisotropic magnetoresistance in simple films, where the magnetoresistance curves are associated to the competitions enter the energies Zeeman and of anisotropic magnetic. The effect of AMR was verifies for the samples of films nanometric's through numeric simulation. For the development of the research, we set up a Device of Variation of Magnetic Field DC (DVCM DC) and the experimental data are obtained through virtual instrumentation. The magnetoresistance curves were interpreted in agreement with the model phenomenological and we still used the hysteresis loop obtained by MOKE as parameters. / No presente trabalho de dissertação do curso de mestrado, estudamos as propriedades magnéticas de filmes nanométricos simples como: ferro sobre óxido de magnésio (Fe/MgO) e permalloy (Fe Ni) em temperatura ambiente, obtidos pelo processo de eltro-deposição por sputtering. Os resultados experimentais foram interpretados de acordo com os modelos fenomenológicos que levam em conta os termos mais relevantes da energia livre magnética do sistema. Fizemos uma abordagem em conformidade com a literatura sobre os principais mecanismos que originam a resistência elétrica em filmes metálicos magnéticos, tais como: resistência elétrica ôhmica, efeito Hall, magnetoresistência anisotrópica (AMR). É feita uma descrição das principais técnicas experimentais usadas na caracterização de filmes nanométricos, como o Magnetômetro de Efeito Kerr Magneto-óptico (MOKE), Ressonância Ferromagnética (FMR) e Magneto-resistência (MR). Esta última técnica, que usa o método das quatro pontas, é utilizada para obter as curvas de magneto-resistência. Neste trabalho, estudamos o efeito da magneto-resistência anisotrópica em filmes simples, onde as curvas de magnetoresistência estão associadas às competições entre as energias Zeeman e de anisotropia magnética. O efeito da AMR foi verificado para as amostras de filmes nanométricos via simulação numérica. Para o desenvolvimento da pesquisa, montamos um Dispositivo de Variação de Campo Magnético DC (DVCM DC) e os dados experimentais são obtidos via instrumentação virtual. As curvas de magneto-resistência foram interpretadas de acordo com o modelo fenomenológico e utilizamos ainda as curvas de histerese, obtidas por MOKE como parâmetros.

Data storage in current hard disk drives is limited by three factors. These are thermal stability of recorded data, the ability to store data, and the ability to read back the stored data. An attempt to alleviate one factor can affect others. This ultimately limits magnetic recording densities that can be achieved using traditional forms of data storage. In order to advance magnetic recording and postpone these inhibiting factors, new approaches are required. One approach is recording on Bit Patterned Media (BPM) where the medium is patterned into nanometer-sized magnetic islands where each stores a binary digit.This thesis presents a statistical model of write errors in BPM composed of single domain islands. The model includes thermal activation in a calculation of write errors without resorting to time consuming micromagnetic simulations of huge populations of islands. The model incorporates distributions of position, magnetic and geometric properties of islands. In order to study the impact of island geometry variations on the recording performance of BPM systems, the magnetometric demagnetising factors for a truncated elliptic cone, a generalised geometry that reasonably describe most proposed island shapes, were derived analytically.The inclusion of thermal activation was enabled by an analytic derivation of the energy barrier for a single domain island. The energy barrier is used in a calculation of transition rates that enable the calculation of error rates. The model has been used to study write-error performance of BPM systems having distributions of position, geometric and magnetic property variations. Results showed that island intrinsic anisotropy and position variations have a larger impact on write-error performance than geometric variations.The model was also used to study thermally activated Adjacent Track Erasure (ATE) for a specific write head. The write head had a rectangular main pole of 13 by 40 nm (cross-track x down-track) with pole trailing shield gap of 5 nm and pole side shield gap of 10 nm. The distance from the pole to the top surface of the medium was 5 nm, the medium was 10 nm thick and there was a 2 nm interlayer between the soft underlayer (SUL) and the medium, making a total SUL to pole spacing of 17 nm. The results showed that ATE would be a major problem and that cross-track head field gradients need to be more tightly controlled than down-track. With the write head used, recording at 1 Tb/in² would be possible on single domain islands.

Orientador: Hugo Enrique Hernández Figueroa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T15:57:35Z (GMT). No. of bitstreams: 1 ArrietaConcha_JoseLuis_M.pdf: 2860251 bytes, checksum: a9513ec6b0227b83e8ccdb097adfef27 (MD5) Previous issue date: 2014 / Resumo: Redes de comunicação ópticas são parte da sociedade de informação de hoje, em que as fibras ópticas têm um papel muito importante, uma vez que são amplamente utilizados em redes de comunicação e outros sistemas de comunicação atuais. No entanto, o uso de dispositivos eletrônicos em várias redes eletro-ópticas representam um grande engarrafamento para a utilização ideal da grande largura de banda e as taxas de dados de alta velocidade permitida por fibras ópticas. A fim de evitar tal congestionamento de tráfego da rede, dispositivos baseados em tecnologias fotônicas são uma das soluções propostas, porque eles fornecem a capacidade de manter altas velocidades de transmissão com taxas elevadas de dados e baixas perdas. Por isso, tais dispositivos fotônicos são continuamente pesquisados, a fim de melhorar a sua eficácia, a obtenção do maior confinamento e encaminhamento do sinal óptico, e melhorar a perda de inserção quando ele é integrado com outros dispositivos. Para alcançar uma maior compreensão dos dispositivos fotônicos, o trabalho apresentado aqui permite uma compreensão pedagógica e ainda completa de cristais fotônicos e efeitos magnéticos. Esta abordagem pedagógica permite uma experiência em mãos para os estudantes e pesquisadores sobre um tema complexo, um tipo de implementação experimental que normalmente exige sofisticados recursos de fabricação fotônicos. A abordagem em micro-ondas permite construir protótipos conceitualmente equivalentes e manipuláveis. Aqui, apresentamos um estudo teórico, análise numérica, modelagem de computador e simulações eletromagnéticas para um circulador de ferrita de 3 portas em uma estrutura de grade fotônico construído para a faixa de micro-ondas de 2,3GHz - 2,9GHz / Abstract: Optical communication networks are part of today¿s information based society, in which optical fibers play a very important role, since they are widely used in such communication networks and other state of the art communication systems. However, the use of electronic devices in various electronic-optical networks represent a major bottleneck for the optimal utilization of the large bandwidth and high speed data rates allowed by optical fibers. In order to avoid such congestion of network traffic, devices based on photonic technologies are one of the proposed solutions, because they provide the capability to maintain transmission speeds with both high data rates and low losses. That is why such photonic devices are continuously being researched in order to improve their effectiveness, obtain greater confinement and guiding of the optical signal, as well as to reduce the insertion loss when it is integrated with other devices. To achieve a greater understanding of photonic devices, the work presented in this paper allow for a pedagogical and yet thorough understanding of photonic crystals and magnetic effects. This pedagogical approach permits a hands-on experience for students and researchers on a complex subject, a kind of experimental implementation that usually demands sophisticated photonic fabrication resources. The microwave approach allows one to construct conceptually equivalent but hand-manipulable prototypes. Here, we present the theoretical study, numerical analysis, computer modeling and electromagnetic simulations for a 3-port ferrite circulator in a photonic grid structure built for the 2.3 GHz to 2.9 GHz microwave range. For a photonic device operating in the optical communication range, we may expect a qualitative analogous behavior / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

abstract: Single-layer pentagonal materials have received limited attention compared with their counterparts with hexagonal structures. They are two-dimensional (2D) materials with pentagonal structures, that exhibit novel electronic, optical, or magnetic properties. There are 15 types of pentagonal tessellations which allow plenty of options for constructing 2D pentagonal lattices. Few of them have been explored theoretically or experimentally. Studying this new type of 2D materials with density functional theory (DFT) will inspire the discovery of new 2D materials and open up applications of these materials in electronic and magnetic devices.In this dissertation, DFT is applied to discover novel 2D materials with pentagonal structures. Firstly, I examine the possibility of forming a 2D nanosheet with the vertices of type 15 pentagons occupied by boron, silicon, phosphorous, sulfur, gallium, germanium or tin atoms. I obtain different rearranged structures such as a single-layer gallium sheet with triangular patterns. Then the exploration expands to other 14 types of pentagons, leading to the discoveries of carbon nanosheets with Cairo tessellation (type 2/4 pentagons) and other patterns. The resulting 2D structures exhibit diverse electrical properties. Then I reveal the hidden Cairo tessellations in the pyrite structures and discover a family of planar 2D materials (such as PtP2), with a chemical formula of AB2 and space group pa ̄3. The combination of DFT and geometries opens up a novel route for the discovery of new 2D materials. Following this path, a series of 2D pentagonal materials such as 2D CoS2 are revealed with promising electronic and magnetic applications. Specifically, the DFT calculations show that CoS2 is an antiferromagnetic semiconductor with a band gap of 2.24 eV, and a N ́eel temperature of about 20 K. In order to enhance the superexchange interactions between the ions in this binary compound, I explore the ternary 2D pentagonal material CoAsS, that lacks the inversion symmetry. I find out CoAsS exhibits a higher Curie temperature of 95 K and a sizable piezoelectricity (d11=-3.52 pm/V). In addition to CoAsS, 34 ternary 2D pentagonal materials are discovered, among which I focus on FeAsS, that is a semiconductor showing strong magnetocrystalline anisotropy and sizable Berry curvature. Its magnetocrystalline anisotropy energy is 440 μeV/Fe ion, higher than many other 2D magnets that have been found. Overall, this work not only provides insights into the structure-property relationship of 2D pentagonal materials and opens up a new route of studying 2D materials by combining geometry and computational materials science, but also shows the potential applications of 2D pentagonal materials in electronic and magnetic devices. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

<div> <div> <div> <p>Process variations and increasing leakage current are major challenges toward memory realization in deeply-scaled CMOS devices. Spintronic devices recently emerged as one of the leading candidates for future information storage due to its potential for non-volatility, high speed, low power and good endurance. In this thesis, we start with the basic concepts and applications of three spintronic devices, namely spin or- bit torque (SOT) based spin-valves, SOT-based magnetic tunnel junctions and the magnetic skyrmion (MS) for both logic and machine learning hardware. </p> <p>We propose a new Spin-Orbit Torque based Domino-style Spin Logic (SOT-DSL) that operates in a sequence of Preset and Evaluation modes of operations. During the preset mode, the output magnet is clocked to its hard-axis using spin Hall effect. In the evaluation mode, the clocked output magnet is switched by a spin current from the preceding stage. The nano-magnets in SOT-DSL are always driven by orthogonal spins rather than collinear spins, which in turn eliminates the incubation delay and allows fast magnetization switching. Based on our simulation results, SOT-DSL shows up to 50% improvement in energy consumption compared to All-Spin Logic. Moreover, SOT-DSL relaxes the requirement for buffer insertion between long spin channels, and significantly lowers the design complexity. This dissertation also covers two applications using MS as information carriers. MS has been shown to possess several advantages in terms of unprecedented stability, ultra-low depinning current density, and compact size. </p><p><br></p><p>We propose a multi-bit MS cell with appropriate peripheral circuits. A systematic device-circuit-architecture co-design is performed to evaluate the feasibility of using MS-based memory as last-level caches for general purpose processors. To further establish the viability of skyrmions for other applications, a deep spiking neural network (SNN) architecture where computation units are realized by MS-based devices is also proposed. We develop device architectures and models suitable for neurons and synapses, provide device-to-system level analysis for the design of an All-Spin Spiking Neural Network based on skyrmionic devices, and demonstrate its efficiency over a corresponding CMOS implementation.</p> <div> <div> <div> <p><br></p><p>Apart from the aforementioned applications such as memory storage elements or logic operation, this research also focuses on the implementation of spin-based device to solve combinatorial optimization problems. Finding an efficient computing method to solve these problems has been researched extensively. The computational cost for such optimization problems exponentially increases with the number of variables using traditional von-Neumann architecture. Ising model, on the other hand, has been proposed as a more suitable computation paradigm for its simple architecture and inherent ability to efficiently solve combinatorial optimization problems. In this work, SHE-MTJs are used as a stochastic switching bit to solve these problems based on the Ising model. We also design an unique approach to map bi-prime factorization problem to our proposed device-circuit configuration. By solving coupled Landau- Lifshitz-Gilbert equations, we demonstrate that our coupling network can factorize up to 16-bit binary numbers. </p> </div> </div> </div> </div> </div> </div>

No description available.

We performed atomistic modeling to study magnetic, mechanical, and thermal properties of materials. We executed molecular statics and dynamics simulations for this study, using density functional theory (DFT) and semi-empirical methods, such as embedded atom method (EAM) and modified embedded atom method (MEAM) potentials. In our first study, we showed that when Al atoms are substituted in barium hexaferrite, the total magnetization monotonically decreases due to the fact that Al atoms preferentially occupy the majorly contributing magnetic sites. The second study was to explore the diffusion mechanism of Ba atoms in hematite in order to study new techniques to build spherical nano-magnetic-particles. In the third study, we showed tungsten carbide growth is inhibited in the presence of vanadium carbide. In the fourth study, we showed how the mechanical and thermal properties of iron changes with vanadium doping with a newly developed MEAM interatomic potential. The physical properties of calcium were calculated in the next study, by the development of a MEAM potential which can be used for multiscale modeling. In the sixth study, the melting temperature of nanoparticles was analyzed and shown to decrease with a decrease of its size, confirming that the bulk properties of the material significantly change in its nano counterpart. Finally a portion of this research was dedicated for the simulation of sintering mechanisms of tungsten nanoparticles at different temperatures and pressures. While the first three studies were based on DFT, the last four studies focused on understanding physical phenomena using EAM/MEAMpotentials.