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1
Rondinone, Adam Justin. "Superparamagnetic relaxation dynamics of magnetic spinel ferrite nanoparticles." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/30958.
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Chen, Ritchie. "Optimizing hysteretic power loss of magnetic ferrite nanoparticles." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81064.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis. "June 2013."
Includes bibliographical references (p. 44-46).
This thesis seeks to correlate hysteretic power loss of tertiary ferrite nanoparticles in alternating magnetic fields to trends predicted by physical models. By employing integration of hysteresis loops simulated from physical models for single-domain ferromagnets, we have identified ferrite materials optimal for remote heating. Several organometallic thermal decomposition methods were adapted to synthesize nanoparticles with anisotropy energies varying over 3 orders of magnitude and transferred into water using a high-temperature ligand exchange protocol. Furthermore, we compare nanoparticles of the same composition and size produced via different synthesis conditions and highlight differences in their materials properties. These analyses identify the synthesis conditions that yield nanoparticles with optimized magnetic properties and with some of the highest power dissipation (specific loss power) found in literature for tertiary ferrite materials.
by Ritchie Chen.
S.M.
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Vestal, Christy Riann. "Magnetic couplings and superparamagnetic properties of spinel ferrite nanoparticles." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-06072004-131405/unrestricted/vestal%5Fchristy%5Fr%5F200405%5Fphd.pdf.
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Dondero, Russell A. "Silica coating of spinel ferrite nanoparticles." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/27375.
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Han, Man Huon. "Development of synthesis method for spinel ferrite magnetic nanoparticle and its superparamagnetic properties." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26465.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.Committee Chair: Z. John Zhang; Committee Member: Angus Wilkinson; Committee Member: C P Wong; Committee Member: E. Kent Barefield; Committee Member: Mostafa El-Sayed. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Vaughan, Lisa Ann. "Enviromentally benign synthesis and application of some spinel ferrite nanopartilces." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44876.
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In this thesis, the commercial viability of the aminolytic synthesis method is explored through robustness, versatility, and waste reduction studies. We report the preparation of metal precursors and the development of a synthetic approach using an aminolytic reaction of metal carboxylates in oleylamine and non-coordinating solvent. Manganese doping in the cobalt ferrites allows for the investigation of the couplings. All the compositions in the series Co1-xMnxFe2O4, 0.0 x 1.0 were synthesized via the aminolytic reaction. The coercivity decreases with increasing Mn2+ concentration due to reducing of high magnetic anisotropy ion (Co2+) content. To our knowledge, this work is the first completed series of Co1-xMnxFe2O4. The method is used to synthesize manganese ferrites dope with chromium. This allows for the investigation of the effects of orbital momentum quantum coupling. All the compositions of MnFe2-xCrxO4, x= 0.0, 0.05, 0.13, 0.25, 0.43, 0.62, and 0.85, were synthesized via the In-situ aminolytic method. Chromium concentration weakens the couplings resulting in the decrease in overall magnetic moment. All by-products can be recycled for re-utilization. The "mother" solution can be used for multiple batches without treatment. Our trials have shown that the reaction could undergo ten reactions using the same solution without scarifying the quality or yield of the product. Finally, an environmental application is explored through the use of iron oxides. Samples of goethite, maghemite, magnetite, and hematite were synthesized and characterized. These nanoparticles were exposed to arsenic and chromium solutions to measure the percent uptake of contaminant by each phase. Adsorption isotherms were plotted to obtain Freundlich parameters. The adsorption constant (K) averages over a 400% increase on literature values. We synthesized hematite and maghemite core-shell particles and exposed them to arsenite and maghemite core-shell particles have the higher removal affinity due to their smaller size.
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Cripps, Chala Ann. "Synthesis and characterization of cobalt ferrite spinel nanoparticles doped with erbium." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/30855.
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Gradzki, Pawel Miroslaw. "Core loss characterization and design optimization of high-frequency power ferrite devices in power electronics applications." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-165934/.
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Samia, Anna Cristina S. "Design and control of the superparamagnetic properties of cobalt-based spinel ferrite nanoparticles." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/31048.
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Scarberry, Kenneth Edward. "Biomedical applications of cobalt-spinel ferrite nanoparticles for cancer cell extraction and drug delivery." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33951.
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In this presentation it is demonstrated that the unique magnetic properties of superparamagnetic cobalt-spinel ferrite nanoparticles can be employed in several novel applications. A method to selectively capture and remove pathogens from infected organisms to improve longevity is presented. Evidence is provided to show that automated methods using modified forms of hemofiltration or peritoneal dialysis could be used to eliminate the particle/pathogen or particle/infected cell conjugates from the organism postoperatively. It is shown that disparately functionalized nanoparticles can be used in concert as drug carrier and release mechanisms. Lastly, we provide preliminary evidence to support the use of magnetic nanoparticles for controlling reaction kinetics.
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Washburn, Cody. "Electrophoretic deposition of ferrite for on chip copper planar inductors /." Online version of thesis, 2006. http://hdl.handle.net/1850/5196.
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Ring, Andrew Phillip. "Investigation of magnetic and magnetoelastic properties of novel materials involving cobalt ferrite and terbium silicon germanium systems." [Ames, Iowa : Iowa State University], 2007.
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Martin, Lara Jean. "Flexible magnetic composite for antenna applications in radio frequency identification (RFID)." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22599.
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Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Dr. C. P. Wong; Committee Co-Chair: Dr. Manos Tentzeris; Committee Member: Dr. Hamid Garmestani; Committee Member: Dr. Meilin Liu; Committee Member: Dr. Z. L. Wang.
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Apaydin, Nil. "Novel Implementations of Coupled Microstrip Lines on Magnetic Substrates." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373897365.
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Arrieta, Concha José Luis 1981. "Study of a ferrite circulator for PBG waveguides in the microwave band : Estudo de um circulador de ferrita para guias PBG na faixa de micro-ondas." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259175.
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Orientador: Hugo Enrique Hernández FigueroaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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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
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Song, Qing. "Size and Shape Controlled Synthesis and Superparamagnetic Properties of Spinel Ferrites Nanocrystals." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7645.
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Size and Shape Controlled Synthesis and Superparamagnetic Properties of Spinel Ferrites Nanocrystals
Qing Song
216 pages
Directed by Dr. Z. John Zhang
The correlationship between magnetic properties and magnetic couplings is established through the investigations of various cubic spinel ferrite nanocrystals. The results of this thesis contribute to the knowledge of size and shape controlled synthesis of various spinel ferrites and core shell architectured nanocrystals as well as the nanomagnetism in spinel ferrites by systematically investigating the effects of spin orbital coupling, magnetocrystalline anisotropy, exchange coupling, shape and surface anisotropy upon superparamagnetic properties of spinel ferrite nanocrystals. A general synthetic method is developed for size and shape control of metal oxide nanocrystals. The size and shape dependent superparamagnetic properties are discussed. The relationship between spin orbital coupling and magnetocrystalline anisotropy is studied comparatively on variable sizes of spherical CoFe2O4 and Fe3O4 nanocrystals. It also addresses the effect of exchange coupling between magnetic hard phase and soft phase upon magnetic properties in core shell structured spinel ferrite nanocrystals. The role of anisotropic shapes of nanocrystals upon self assembled orientation ordered superstructures are investigated. The effect of thermal stability of molecular precursors upon size controlled synthesis of MnFe2O4 nanocrystals and the size dependent superparamagnetic properties are described.
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Toledo, Dennis. "Cobalt Ferrite Nanoparticles Fabricated via Co-precipitation in Air: Overview of Size Control and Magnetic Properties." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2298.
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Cobalt Ferrite has important, size-dependent magnetic properties. Consequently, an overview of particle size is important. Co-precipitation in air was the fabrication method used because it is comparatively simple and safe. The effects of three different reaction times including 1, 2, 3 hour(s) on particle size were compared. Also, the effectiveness of three different capping agents (Oleic Acid, Polyvinylpyrollidone (PVP), and Trisodium Citrate) in reducing aggregation and correspondingly particle size were examined. Using Welch’s analysis of variance (ANOVA) and the relevant post hoc tests, there was no significant difference (p=0.05) between reaction times of 1 hour and 2 hours, but there was a significant difference between reaction times of 2 hours and 3 hours. Potentially, because of increased coarsening for the 3 hour reaction time. PVP and Oleic Acid were shown to be effective in reducing aggregation; however, Citrate was not effective. Possibly, the synthesis procedure was inadequate.
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Crain, Bruce Richard. "Vector finite element methods for spurious-free solutions of unbounded dielectric and ferrite loaded waveguiding structures." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15501.
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Camus, Olivier. "Modélisation des propriétés magnétiques de matériaux ferrite et de composites à base de ferrite absorbant le rayonnement électromagnétique." Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL022N.
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Cette étude porte sur la modélisation de la perméabilité magnétique de ferrites pour leur utilisation en tant qu'absorbants aux ondes hyperfréquences. Les ferrites étudiés se trouvent sous la forme de matériaux frittés ou de composites. L’absorption d'une onde électromagnétique par des ferrites frittés est provoquée par la rotation de l'aimantation dans des domaines magnétiques et par le déplacement des parois entre ces domaines. Nous développons des modèles basés sur l'association de phénomènes résonants et/ou relaxants pour représenter la dépendance en fréquence de la perméabilité magnétique. Ces différents modèles sont validés expérimentalement pour déterminer celui qui représente le mieux les mesures de perméabilité de ferrites frittés ou de composites à base de ferrite. Les matériaux composites sont constitués d'une matrice polymère non magnétique au sein de laquelle sont dispersées des particules magnétiques de ferrite. De nombreuses lois de mélange ont été développées dans le but de modéliser la perméabilité de tels matériaux. Certaines de ces lois, basées sur l'approximation quasi-statique ou sur l'hypothèse du milieu effectif, sont appliquées à des mesures expérimentales. Cependant, ces lois, au contraire de la loi du milieu effectif généralisé (GEM), ne peuvent représenter la transition entre l'état non magnétique et l'état magnétique du composite à la percolation. L’analyse d'image effectuée sur les composites permet de valider les paramètres de la GEM et de vérifier si cette loi peut devenir prédictive
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RIBEIRO, THATIANA G. D. "Sintese e caracterizacao de nanoparticulas magneticas de oxidos mistos de MnFesub(2)Osub(4) recobertas comm quitosona. Estudos da influencia na dopagem com Gdsup(3+) nas propriedades estruturais e magneticas." reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11515.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Mukherjee, Devajyoti. "Growth and Characterization of Epitaxial Thin Films and Multiferroic Heterostructures of Ferromagnetic and Ferroelectric Materials." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3622.
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Multiferroic materials exhibit unique properties such as simultaneous existence of
two or more of coupled ferroic order parameters (ferromagnetism, ferroelectricity,
ferroelasticity or their anti-ferroic counterparts) in a single material. Recent years have
seen a huge research interest in multiferroic materials for their potential application as
high density non-volatile memory devices. However, the scarcity of these materials in
single phase and the weak coupling of their ferroic components have directed the
research towards multiferroic heterostructures. These systems operate by coupling the
magnetic and electric properties of two materials, generally a ferromagnetic material and
a ferroelectric material via strain. In this work, horizontal heterostructures of composite
multiferroic materials were grown and characterized using pulsed laser ablation technique.
Alternate magnetic and ferroelectric layers of cobalt ferrite and lead zirconium titanate,
respectively, were fabricated and the coupling effect was studied by X-ray stress analysis.
It was observed that the interfacial stress played an important role in the coupling effect
between the phases. Doped zinc oxide (ZnO) heterostructures were also studied where
the ferromagnetic phase was a layer of manganese doped ZnO and the ferroelectric phase
was a layer of vanadium doped ZnO. For the first time, a clear evidence of possible room
temperature magneto-elastic coupling was observed in these heterostructures. This work
provides new insight into the stress mediated coupling mechanisms in composite
multiferroics.
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Zagnazi, Hassan. "Preparation et etude de l'hexaferrite de baryum par la voie verriere." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13071.
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Obtention de l'hexaferrite de baryum bafe::(12)o::(19) par cristallisation dans un verre bao-b::(2)o::(3); la cristallisation passe par bafe::(2)o::(4), et b::(2)o::(3) joue un role determinant, le choix de la composition de depart etant tres important (l'exces de b::(2)o::(3) reagit sur bafe::(12)o::(10) et diminue son rendement). Les poudres d'hexaferrite de baryum preparees presentent une aimantation qui varie de 60 a 68 uemcgs/g et un champ coercitif qui descend de 5000 oe a 1600 oe. Les mesures magnetiques des verres etudies montrent un comportement "verre de spin
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Fechine, Pierre BasÃlio Almeida. "Estudo das propriedades estruturais e elÃtricas das granadas ferrimagnÃticas GdIGXYIG1-X e suas aplicaÃÃes em componentes de microondas." Universidade Federal do CearÃ, 2008. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=1389.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorDevido ao rÃpido progresso no desenvolvimento de sistemas de comunicaÃÃo em microondas, as cerÃmicas dielÃtricas e magnÃticas (ferritas) se tornaram atrativas para o uso em dispositivos. Embora as ferritas do tipo espinel terem sido os primeiros materiais utilizados para microondas, as granadas possuem menores perdas dielÃtricas e, portanto, sÃo preferidas em muitas aplicaÃÃes. As elevadas exigÃncias que as aplicaÃÃes elÃtricas modernas requerem dos materiais magnÃticos fazem com que novas tÃcnicas e produtos estejam permanentemente sendo pesquisados, com o conseqÃente aparecimento de novas soluÃÃes para uma ampla sÃrie de aplicaÃÃes. Nesse sentido, a pesquisa sobre compÃsitos à empregada para a busca de novos materiais. Este trabalho apresenta a obtenÃÃo do compÃsito ferrimagnÃtico, constituÃdo pelas fases Y3Fe5O12 (YIG) e Gd3Fe5O12 (GdIG), atravÃs da rota sintÃtica no estado sÃlido com a utilizaÃÃo de moagem mecÃnica de alta energia. A DifraÃÃo de Raios-X, a Espectroscopia Raman, Infravermelho e MÃssbauer foram essenciais para caracterizaÃÃo estrutural dos compÃsitos. As peculiaridades da morfologia das amostras foram elucidadas pela Microscopia EletrÃnica de Varredura e Microdureza de Vickers. Adicionalmente, foram realizados experimentos para se avaliar o comportamento elÃtrico e magnÃtico dos compÃsitos na faixa de radio freqÃÃncia e de microondas para depois sugerir uma aplicaÃÃo tecnolÃgica cabÃvel. Os compÃsitos comportaram-se adequadamente como antenas ressoadoras de ferritas (FRAs) e de microlinha (filmes espessos depositados sobre a superfÃcie metalizada de um substrato de alumina, pela tÃcnica âscreen printingâ), na faixa de operaÃÃo das microondas. Os experimentos com os FRAs se mostraram satisfatÃrios devido ao controle das caracterÃsticas de radiaÃÃo das antenas e a sua sintonizaÃÃo pela aplicaÃÃo de um campo magnÃtico externo. As mesmas tiveram a caracterÃstica de antenas de banda larga. Os ressoadores provenientes dos compÃsitos projetados neste trabalho podem ser importantes para desenvolver uma antena de banda larga de terceira geraÃÃo (3G) para telefones celulares e outros produtos para redes sem fio.
Devido ao rÃpido progresso no desenvolvimento de sistemas de comunicaÃÃo em microondas, as cerÃmicas dielÃtricas e magnÃticas (ferritas) se tornaram atrativas para o uso em dispositivos. Embora as ferritas do tipo espinel terem sido os primeiros materiais utilizados para microondas, as granadas possuem menores perdas dielÃtricas e, portanto, sÃo preferidas em muitas aplicaÃÃes. As elevadas exigÃncias que as aplicaÃÃes elÃtricas modernas requerem dos materiais magnÃticos fazem com que novas tÃcnicas e produtos estejam permanentemente sendo pesquisados, com o conseqÃente aparecimento de novas soluÃÃes para uma ampla sÃrie de aplicaÃÃes. Nesse sentido, a pesquisa sobre compÃsitos à empregada para a busca de novos materiais. Este trabalho apresenta a obtenÃÃo do compÃsito ferrimagnÃtico, constituÃdo pelas fases Y3Fe5O12 (YIG) e Gd3Fe5O12 (GdIG), atravÃs da rota sintÃtica no estado sÃlido com a utilizaÃÃo de moagem mecÃnica de alta energia. A DifraÃÃo de Raios-X, a Espectroscopia Raman, Infravermelho e MÃssbauer foram essenciais para caracterizaÃÃo estrutural dos compÃsitos. As peculiaridades da morfologia das amostras foram elucidadas pela Microscopia EletrÃnica de Varredura e Microdureza de Vickers. Adicionalmente, foram realizados experimentos para se avaliar o comportamento elÃtrico e magnÃtico dos compÃsitos na faixa de radio freqÃÃncia e de microondas para depois sugerir uma aplicaÃÃo tecnolÃgica cabÃvel. Os compÃsitos comportaram-se adequadamente como antenas ressoadoras de ferritas (FRAs) e de microlinha (filmes espessos depositados sobre a superfÃcie metalizada de um substrato de alumina, pela tÃcnica âscreen printingâ), na faixa de operaÃÃo das microondas. Os experimentos com os FRAs se mostraram satisfatÃrios devido ao controle das caracterÃsticas de radiaÃÃo das antenas e a sua sintonizaÃÃo pela aplicaÃÃo de um campo magnÃtico externo. As mesmas tiveram a caracterÃstica de antenas de banda larga. Os ressoadores provenientes dos compÃsitos projetados neste trabalho podem ser importantes para desenvolver uma antena de banda larga de terceira geraÃÃo (3G) para telefones celulares e outros produtos para redes sem fio.
Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. In this sense, the research in composites is employed to reach new materials. This work presents the study of the ferrimagnetic composite, constituted by Y3Fe5O12 (YIG) and Gd3Fe5O12 (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. The X-Ray Diffraction and the Raman, Infrared and MÃssbauer Spectroscopy were essential for the structural characterization of the composites. The peculiarities in the morphology of the samples were elucidated by Scanning Electron Microscopy and Vickers Microhardness. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screen-printing technique), in the microwave frequency range. The experiments with FRAs showed satisfactory due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. They present a wideband antenna profile. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.
Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. In this sense, the research in composites is employed to reach new materials. This work presents the study of the ferrimagnetic composite, constituted by Y3Fe5O12 (YIG) and Gd3Fe5O12 (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. The X-Ray Diffraction and the Raman, Infrared and MÃssbauer Spectroscopy were essential for the structural characterization of the composites. The peculiarities in the morphology of the samples were elucidated by Scanning Electron Microscopy and Vickers Microhardness. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screenprinting technique), in the microwave frequency range. The experiments with FRAs showed satisfactory due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. They present a wideband antenna profile. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.
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Ibrahim, Fatima. "Theoretical study of electronic structure and magnetism in materials for spintronics." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE003/document.
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L'avenir de la spintronique repose sur le développement de matériaux ayant des propriétés magnétiques remarquables. L'objectif de cette thèse est de comprendre la physique des deux matériaux fonctionnels proposés pour des applications spintroniques qui utilisent des simulations de la densité fonctionnelle.Nous nous sommes intéressés dans une première partie au ferrite de gallium pour lequel il a été montré que les propriétés dépendaient de la concentration de fer.Les spectres optiques ont été calculés et comparés aux spectres expérimentaux suggérant des niveaux élevés de désordre. Dans la deuxième partie, nous avons montré une polarisation de spin à l’interface hybride formée entre la phthalocyanine de manganèse et la surface de cobalt,en accord avec les expériences de photoémission.La formation de la spinterface a été expliquée par différents mécanismes d'hybridation dans chaque canal de spin.Cette polarisation de spin est coordonnée avec des moments magnétiques induits sur les sites moléculairesThe future of the spintronics technology requires developing functional materials with remarkable magnetic properties. The aim of this thesis is to understand the physics of functional materials proposed for spintronic applications using ab-initio density functional simulations. We investigated the properties of two different functional materials. We first studied the magnetoelectric gallium ferrite GFO. The dependence of the different properties on the iron concentration has been demonstrated and discussed. The optical spectra were calculated and compared to the experimental once suggesting high levels of iron disorder. In the second part, we demonstrated a highly spin polarized hybrid interface formed between manganese phthalocyanine and cobalt surface in agreement with photoemission experiments. The formation of this spinterface was described by different hybridization mechanisms in each spin channel. This high spin polarization is coordinated with induced magnetic moments on the molecular sites
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Orlando, Andrea. "Numerical modeling and analysis of complex electromagnetic structures, including those containing ferrites." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Orlando_09007dcc80705498.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 17, 2009) Includes bibliographical references (p. 83-84).
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Hudson, Guy Frederick, and Guy Frederick Hudson. "Surface chemistry of magnetic oxides and ferrites and their interaction with selected components of magnetic inks." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184919.
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Studies to compare and elucidate some of the surface chemical characteristics of chromium dioxide and barium ferrite magnetic particles have been performed. These investigations primarily involved using the technique of flow microcalorimetry to look at the interaction of molecular probes (pyridine, 4-nitrophenol) and various components present in a magnetic ink (dispersants and model binder compounds) with the particles. The interactions were measured in terms of heats of adsorption and adsorption density. Ancillary experiments using FTIR and XPS were also performed. Both electrophoretic measurements and calorimetric studies showed that stabilized CrO₂ was less acidic than un-stabilized CrO₂. Similar measurements showed that un-doped barium ferrite was more acidic than Co and Ti doped barium ferrite. The interactions of dispersants and model binder components with barium ferrite were found to be very exothermic; heats of interaction of greater than -20 kcal/mole were not uncommon. Subsequent analysis of barium ferrite particles treated with dispersants and binder compounds using FTIR and XPS suggested that these compounds formed chemical complexes on the surface of the ferrite particles.
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Pessoa, R?gia Chacon. "Estudo das caracter?sticas magn?ticas e absorvedoras das ferritas de nizn, niznmn, mnzn, nimg, nicuzn e nicuznmg obtidas via m?todo do citrato precursor." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/17716.
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Previous issue date: 2009-12-22Universidade Estadual de Roraima
Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350?C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100?C/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500?C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100?C/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100?C/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements, indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation.
Foram sintetizados os sistemas Ni0,5Zn0,5Fe2O4, Ni0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 e Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, pelo m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada por an?lise termogravim?trica e espectroscopia na regi?o do infravermelho, na temperatura de 350?C/3h. A evolu??o das fases formadas ap?s as calcina??es a 350, 500, 900 e 1100?C/3h foi acompanhada por difra??o de raios X utilizando o refinamento de Rietveld, para melhor identifica??o das estruturas formadas. Os materiais foram tamb?m analisados por microscopia eletr?nica de varredura, medidas magn?ticas e an?lise da refletividade do material. As amostras calcinadas em diferentes temperaturas indicaram um aumento da cristalinidade com o aumento da temperatura de calcina??o, verificando-se que, para algumas composi??es, em temperaturas acima de 500?C ocorre a precipita??o de segunda fase, como hematita e CuO. As composi??es com mangan?s na estrutura apresentaram processos de difus?o mais lentos devido ao raio i?nico do mangan?s ser maior em rela??o aos outros ?ons substituintes, fato que retarda a estabiliza??o da estrutura espin?lio e favorece a precipita??o de segunda fase. As composi??es com cobre apresentaram precipita??o da fase CuO na temperatura de 900 e 1100?C/3h, fato que ocorre segundo a literatura porque a concentra??o de cobre na estrutura ? maior que 0,25 mol%. As medidas magn?ticas revelaram racter?sticas de um material ferrimagn?tico macio, obtendo-se melhores ar?metros magn?ticos para as ferritas de NiZn e NiCuZnMg em altas temperaturas. As medidas de refletividade mostraram maior absor??o da radia??o eletromagn?tica na faixa de microondas para as amostras calcinadas a 1100?C/3h, que tem maior tamanho do cristalito e em conseq??ncia forma??o de multidom?nios, aumentando a magnetiza??o do material. Os resultados de absor??o concordaram com as medidas magn?ticas, indicando dentre as ferritas estudadas, as de NiZn e NiCuZnMg como melhores absorvedoras da radia??o incidente.
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CAMILO, RUTH L. "Síntese e caracterização de nanopartículas magnéticas de ferrita de cobalto recobertas por 3-aminopropiltrietoxissilano para uso como material híbrido em nanotecnologia." reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11436.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Sabo, Daniel E. "Novel synthesis of metal oxide nanoparticles via the aminolytic method and the investigation of their magnetic properties." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50122.
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Metal oxide nanoparticles, both magnetic and nonmagnetic, have a multitude of applications in gas sensors, catalysts and catalyst supports, airborne trapping agents, biomedicines and drug delivery systems, fuel cells, laser diodes, and magnetic microwaves. Over the past decade, an inexpensive, simple, recyclable, and environmentally friendly large, scale synthesis method for the synthesis of these metal oxide nanoparticles has been sought. Many of the current techniques in use today, while good on the small, laboratory bench scale, suffer from drawbacks that make them unsuitable for the industrial scale. The aminolytic method, developed by Dr. Man Han while working for Dr. Zhang, fits industrial scale-up requirements. The aminolytic method involves a reaction between metal carboxylate(s) and oleylamine in a non-coordinating solvent. This system was shown to produce a range of spinel ferrites. Dr. Lisa Vaughan showed that this method can be recycled multiple times without degrading the quality of the produced nanoparticles. The purpose of this thesis is to test the versatility of the aminolytic method in the production of a wide range of metal oxides as well as various core/shell systems. Chapter 2 explores the effect of precursor carboxylates chain length on the aminolytic synthesis of cobalt ferrite, and manganese ferrite nanoparticles. In Chapter 3, a series of CuxMn1-xFe₂O₄, (x ranges from 0.0 to 0.2), nanoparticles were synthesized via the aminolytic method. This series allows for the investigation of the effects of orbital Jahn-Teller distortion as well as orbital angular momentum on the magnetic properties of this ferrite. The quantum couplings of magnetic ions in spinel ferrites govern their magnetic properties and responses. An understanding of the couplings between these metal ions allows for tailoring magnetic properties to obtain the desired response needed for various applications. Chapter 4 investigates the synthesis of MnO and Mn₃O₄ nanoparticles in pure single phase with high monodispersity. To the best of our knowledge, the range of sizes produced for MnO and Mn₃O₄ is the most extensive, and therefore a magnetic study of these systems shows some intriguing size dependent properties. The final part of this chapter investigates the applicability of the aminolytic method for building a MnO shell on a CoFe₂O₄ core. Chapter 5 explores the synthesis of another metal oxide, ZrO₂ in both the cubic and monoclinic phases with no impurities. The use of the aminolytic method here removes the need for dangerous/expensive precursors or equipment and eliminates the need for extensive high temperature heat treatments that destroy monodispersity which is required for most techniques. The creation of a core/shell system between CoFe₂O₄ and ZrO₂ using the aminolytic method was also tested. This core/shell system adds magnetic manipulation which is especially useful for the recovery of zirconia based photocatalyst. Chapter 6 studies the application of the aminolytic method in the synthesis of yttrium iron garnet (YIG) and yttrium iron perovskite (YIP) nanoparticles. Current synthesis techniques used to produce YIG and YIP nanoparticles often requires high temperatures, sensitive to contamination, which could be eliminated through the use of our method
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Adair, Antony. "Observed super-spin class behavior in Ni₀.₅Zn₀.₅Fe₂O₄ nanoparticles." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Camilo, Ruth Luqueze. ""Síntese e caracterização de nanopartículas magnéticas de ferrita de cobalto recobertas por 3-aminopropiltrietoxissilano para uso como material híbrido em nanotecnologia"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-27092006-135110/.
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Atualmente com o advento da nanociência e nanotecnologia, as nanopartículas magnéticas têm encontrado inúmeras aplicações nos campos da biomedicina, diagnóstico, biologia molecular, bioquímica, catálise, etc. As nanopartículas magnéticas funcionalizadas são constituídas de um núcleo magnético, envolvido por uma camada polimérica com sítios ativos, que podem ancorar metais ou compostos orgânicos seletivos. Estas nanopartículas são consideradas materiais híbridos orgânico-inorgânicos de grande interesse em aplicações comerciais devido à particularidade das propriedades obtidas. Entre as aplicações importantes podemos citar: tratamento por magnetohipertermia, carregadores de fármacos para áreas específicas do corpo, seleção de moléculas específicas, biossensores, melhoria da qualidade de imagens por RMN, etc. O trabalho foi desenvolvido em duas partes: 1) a síntese do núcleo constituído de nanopartículas superparamagnéticas de ferrita de cobalto e, 2) o recobrimento do núcleo por um polímero bifuncional o 3-aminopropiltrietoxissilano. Os parâmetros estudados na primeira parte da pesquisa foram: pH, concentração molar da base, tipo de base, ordem de adição dos reagentes, modo de adição dos reagentes, velocidade de agitação, concentração inicial dos metais, fração molar de cobalto e tratamento térmico. Na segunda parte estudou-se: o pH, a temperatura, o catalisador, a concentração do catalisador, o tempo de reação, a relação H2O/silano, o tipo de meio, o agente umectante e a eficiência do recobrimento em relação ao pH. Os produtos obtidos foram caracterizados pelas técnicas de difratometria de raios-X (DRX), microscopia eletrônica de transmissão (MET), microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS), espectroscopia de emissão atômica (ICP-AES), espectroscopia por infravermelho (FTIR), análises termogravimétricas (TGA/DTGA), calorimetria exploratória diferencial (DSC) e curvas de magnetização (MAV)Nowadays with the appear of nanoscience and nanotechnology, magnetic nanoparticles have been finding a variety of applications in the fields of biomedicine, diagnosis, molecular biology, biochemistry, catalysis, etc. The magnetic functionalized nanoparticles are constituted of a magnetic nucleus, involved by a polymeric layer with active sites, which ones could anchor metals or selective organic compounds. These nanoparticles are considered organic-inorganic hybrid materials and have great interest as materials for commercial applications due to the specific properties. Among the important applications it can be mentioned: magnetohyperthermia treatment, drugs delivery in specific local of the body, molecular recognition, biossensors, enhancement of nuclear magnetic ressonance images quality, etc. This work was developed in two parts: 1) the synthesis of the nucleus composed by superparamagnetic nanoparticles of cobalt ferrite and, 2) the recovering of nucleus by a polymeric bifunctional 3-aminepropyltriethoxysilane. The parameters studied in the first part of the research were: pH, hydroxide molar concentration, hydroxide type, reagent order of addition, reagent way of addition, speed of shake, metals initial concentrations, molar fraction of cobalt and thermal treatment. In the second part it was studied: pH, temperature, catalyst type, catalyst concentration, time of reaction, relation ratios of H2O/silane, type of medium and the efficiency of the recovering regarding to pH. The products obtained were characterized using the following techniques X-ray powder diffraction (DRX), transmission electronic microscopy (MET), scanning electronic microscopy (MEV), spectroscopy of scatterbrained energy spectroscopy (DES), atomic emission spectroscopy (ICP-AES), themogravimetric analysis (TGA/DTGA), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and magnetization curves (VSM)
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Gass, James. "Functional Magnetic Nanoparticles." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4047.
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Nanoparticle system research and characterization is the focal point of this research and dissertation. In the research presented here, magnetite, cobalt, and ferrite nanoparticle systems have been explored in regard to their magnetocaloric effect (MCE) properties, as well as for use in polymer composites. Both areas of study have potential applications across a wide variety of interdisciplinary fields.
Magnetite nanoparticles have been successfully dispersed in a polymer. The surface chemistry of the magnetic nanoparticle proves critical to obtaining a homogenous and well separated high density dispersion in PMMA. Theoretical studies found in the literature have indicated that surface interface energy is a critical component in dispersion. Oleic acid is used to alter the surface of magnetite nanoparticles and successfully achieve good dispersion in a PMMA thin film. Polypyrrole is then coated onto the PMMA composite layer. The bilayer is characterized using cross-sectional TEM, cross-sectional SEM, magnetic characterization, and low frequency conductivity. The results show that the superparmagnetic properties of the as synthesized particles are maintained in the composite.
With further study of the properties of these nanoparticles for real and functional uses, MCE is studied on a variety of magnetic nanoparticle systems. Magnetite, manganese zinc ferrite, and cobalt ferrite systems show significant broadening of the MCE and the ability to tune the peak temperature of MCE by varying the size of the nanoparticles. Four distinct systems are studied including cobalt, cobalt core silver shell nanoparticles, nickel ferrite, and ball milled zinc ferrite. The results demonstrate the importance of surface characteristics on MCE. Surface spin disorder appears to have a large influence on the low temperature magnetic and magnetocalorie characteristics of these nanoparticle systems.
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Silva, Jos? Eves Mendes da. "S?ntese, caracteriza??o de ferritas espin?lio com propriedades magn?ticas e absorvedoras de microondas." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/17768.
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Previous issue date: 2013-03-08Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Were synthesized spinel-type ferrites with general formula Ni0,8Mg0.2-xMxFe2O4, where M represents the doping Mn, Co or Mn + Co simultaneously, x ranges for the values 0.02, 0.05 and 0.1. The value of x was divided by 2 in cases where M equals Mn and Co conjugates. We used the citrate precursor method and heat treatment to obtain the phases at 1100?C. The materials were characterized by XRD, TGA/ DTGA, SEM, MAV and reflectivity measurements by the method of waveguide. Powders to 350?C/3.5 h were crystalline and nanosized. According to the results this temperature all powders have a percentage of ferrite phase over 90%. The composition had the addition of Mn and Co simultaneously showed a higher percentage of secondary phase NiO, 5.8%. The TGA/DTGA curves indicate that this sample reached phase (s) crystalline (s) at lowest temperatures. The X-ray diffractograms of the samples calcined at 350?C and 1100?C were treated with the Rietveld refinament technique. The powders calcined at 1100 ?C/3h in air show to be 100% except spinel phase composition with 0.02 doping. The micrographs show clusters of particles with sizes smaller than 1 μm in calcination temperature of 1100?C which agreed with the result of Rietveld refinement. In the compositions doped with Mn were higher values of magnetization (45.90 and 53.20 Am2/kg), which did not cause high microwave absorption. The theoretical calculation of magnetization (MT) was consistent with the results, considering that there was agreement between the increase of magnetization experimental and theoretical. It was observed that there was the interrelation of the final effect of absorption with the thickness of MARE, the composition of ferrimagnetic materials and in particular the specific values of frequency. The analysis shows that the reflectivity increases in the concentration of cobalt increased the frequency range and also for absorption 10.17 GHz and 84%, respectively. The best result of chemical homogeneity and the value of 2.96 x 10-2 tesla coercive field were crucial for high performance ferrite absorber with 0.1 cobalt. The Cobalt has high magnetocrystalline anisotropy, it is associated with an increased coercive field, Hc. Therefore, this property improves the results of reflectivity of spinel ferrites
Foram sintetizadas ferritas do tipo espin?lio com f?rmula geral Ni0,8Mg0,2-xMxFe2O4, onde M representa os dopantes Mn, Co ou Mn + Co simultaneamente, x varia para os valores 0,02; 0,05 e 0,1. O valor de x foi dividido por 2 nos casos em que M equivale a Mn com Co conjugados. Foi utilizado o m?todo dos citratos precursores e tratamento t?rmico na obten??o das fases a 1100?C. Os materiais foram caracterizados por DRX, TGA/DTGA, MEV, MAV e medidas de refletividade pelo m?todo de guia de ondas. Os p?s a 350?C/3,5h foram cristalinos e nanom?tricos. De acordo com os resultados nesta temperatura todos os p?s apresentam um percentual de fase ferrita superior a 90%. A composi??o que teve a adi??o de Mn e Co simultaneamente apresentou maior percentual de fase secund?ria NiO, 5,8%. As curvas TGA/DTGA indicam que essa amostra alcan?ou fase(s) cristalina(s) em temperaturas mais baixas. Os difratogramas de raios X das amostras calcinadas a 350?C e 1100?C foram tratados pela t?cnica de refinamento Rietveld. Os p?s calcinados a 1100?C/3h em atmosfera ambiente mostram ser 100% de fase espin?lio exceto a composi??o com 0,02 de dopantes. As micrografias apresentam aglomerados de part?culas com tamanhos menores que 1 μm na temperatura de calcina??o de 1100?C, o que concordou com o resultado de refinamento Rietveld. Nas composi??es dopadas com Mn ocorreram os maiores valores de magnetiza??o (45,90 e 53,20 Am2/kg), o que n?o acarretou alta absor??o de microondas. O c?lculo te?rico da magnetiza??o (MT) foi coerente com os resultados, considerando-se que houve concord?ncia entre o aumento das magnetiza??es experimental e te?rica. Observa-se que houve interrela??o do efeito final de absor??o com a espessura do MARE, a composi??o do material ferrimagn?tico em particular e os valores espec?ficos de freq??ncia. A an?lise de refletividade indica que o aumento na concentra??o de cobalto aumentou a faixa de freq??ncia e a absor??o para 10,17 GHz e 84%, respectivamente. O resultado indica que a melhor homogeneidade qu?mica e o valor 2,96 x 10-2 tesla de campo coercitivo foram determinantes para o alto desempenho absorvedor da ferrita com 0,1 de cobalto. O Cobalto tem alta anisotropia magnetocristalina, isto est? associado ao aumento do campo coercitivo, Hc. Portanto, essa propriedade melhora os resultados de refletividade das ferritas espin?lio
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Morber, Jenny Ruth. "1D nanowires understanding growth and properties as steps toward biomedical and electrical application /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24825.
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Thesis (Ph.D.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.Committee Chair: Snyder, Robert; Committee Co-Chair: Wang, Zhong Lin; Committee Member: El-Sayed, Mostafa; Committee Member: Milam, Valeria; Committee Member: Summers, Christopher; Committee Member: Wong, C. P.
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Fulco, Ana Paula Pereira. "Comportamento magn?tico de comp?sitos de matriz polim?rica com adi??o de ferritas." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12799.
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Previous issue date: 2013-09-06Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
Polymer matrix composites offer advantages for many applications due their combination of properties, which includes low density, high specific strength and modulus of elasticity and corrosion resistance. However, the application of non-destructive techniques using magnetic sensors for the evaluation these materials is not possible since the materials are non-magnetizable. Ferrites are materials with excellent magnetic properties, chemical stability and corrosion resistance. Due to these properties, these materials are promising for the development of polymer composites with magnetic properties. In this work, glass fiber / epoxy circular plates were produced with 10 wt% of cobalt or barium ferrite particles. The cobalt ferrite was synthesized by the Pechini method. The commercial barium ferrite was subjected to a milling process to study the effect of particle size on the magnetic properties of the material. The characterization of the ferrites was carried out by x-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM) and vibrating sample magnetometry (VSM). Circular notches of 1, 5 and 10 mm diameter were introduced in the composite plates using a drill bit for the non-destructive evaluation by the technique of magnetic flux leakage (MFL). The results indicated that the magnetic signals measured in plates with barium ferrite without milling and cobalt ferrite showed good correlation with the presence of notches. The milling process for 12 h and 20 h did not contribute to improve the identification of smaller size notches (1 mm). However, the smaller particle size produced smoother magnetic curves, with fewer discontinuities and improved signal-to-noise ratio. In summary, the results suggest that the proposed approach has great potential for the detection of damage in polymer composites structures
Materiais comp?sitos polim?ricos oferecem vantagens para v?rias aplica??es pela combina??o de propriedades como baixa densidade, elevada resist?ncia mec?nica e m?dulo de elasticidade espec?ficos e resist?ncia a corros?o. Entretanto, por n?o serem magnetiz?veis, esses materiais n?o permitem a utiliza??o de t?cnicas de avalia??o n?o destrutivas que utilizem sensores magn?ticos. Ferritas s?o materiais com excelentes propriedades magn?ticas, estabilidade qu?mica e resist?ncia ? corros?o. Devido a essas propriedades esses materiais s?o promissores para o desenvolvimento de comp?sitos de matriz polim?rica com propriedades magn?ticas. Neste trabalho, discos de comp?sitos de fibra de vidro/ep?xi foram produzidos com adi??o de 10% em massa de part?culas de ferrita de cobalto ou de b?rio. A ferrita de cobalto foi sintetizada pelo m?todo Pechini. A ferrita comercial de b?rio foi submetida a um processo de moagem para se estudar o efeito do tamanho de part?cula nas propriedades magn?ticas do material. A caracteriza??o das ferritas foi realizada pelas t?cnicas de difra??o de raio x (DRX), microscopia eletr?nica de varredura (MEV-FEG) e magnetometria de amostra vibrante (MAV). Entalhes circulares com di?metros de 1, 5 e 10 mm foram introduzidos nos discos de comp?sitos com o aux?lio de uma broca para avalia??o n?o-destrutiva por meio da t?cnica de fuga de fluxo magn?tico (MFL). A abordagem apresentada permitiu identificar todos os entalhes introduzidos nos discos. Os resultados indicaram que os sinais magn?ticos medidos nos discos com a ferrita de b?rio sem moagem e de cobalto apresentaram boa correla??o com a presen?a dos entalhes. O processo de moagem por 12 h e 20 h n?o contribuiu para a melhor identifica??o de entalhes de menor dimens?o (1 mm). Entretanto, o menor tamanho de part?cula permitiu produzir curvas magn?ticas mais suaves, com menos descontinuidades e melhor rela??o sinal-ru?do. Em resumo, os resultados sugerem que a abordagem proposta tem grande potencial para a detec??o de falhas em estruturas de materiais comp?sitos polim?ricos
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Kaverine, Evgueni. "Contribution à la conception d'antennes MF, HF et VHF miniatures pour des applications mobiles, terrestres et maritimes." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S152.
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Les objectifs de ce travail concernent l'étude, la conception et la caractérisation d'antennes miniatures actives ou passives, large bande ou bande étroite fonctionnant en bandes MF, HF et VHF. Le manuscrit est divisé en cinq parties : La première partie présente un système de caractérisation d'antennes qui a été développé, validé et utilisé pour tous les aériens conçus. Ce système, basé sur une cellule à plaque parallèles (PPC), permet un large spectre de mesures telles que la mesure du gain, du point de compression, de l'intermodulation et de la sensibilité via une méthode rayonnée, particulièrement intéressante dans le cas des antennes actives intégrées. La deuxième partie concerne les antennes solénoïdales sur ferrite. L'utilisation de simulateurs électromagnétiques 3D a permis d'obtenir des résultats qui sont comparés à la théorie proposée dans la littérature. Les principaux systèmes d'adaptation d'impédance sont également étudiés. La troisième partie met en avant la possibilité de concevoir des antennes à substrat ferromagnétique de géométrie non conventionnelle en utilisant des matériaux composites. Deux antennes miniatures fabriquées et fonctionnant en bande VHF permettent d'illustrer ce point. Dans la quatrième partie, nous présentons un concept d'antennes à substrat ferromagnétique partiellement saturé. L'utilisation d'une source de champ magnétique statique associée à un matériau initialement dispersif permet de constater un certain nombre de phénomènes intéressants, tels que l'amélioration de l'efficacité tout en préservant l'adaptation de l'antenne ou bien la création de directivité sur des antennes électriquement très compactes. La dernière partie présente la valorisation du travail à travers un projet de télécommunication hertzienne longue portée s'inscrivant dans le cadre de la navigation maritimeThe objectives of this work concern the study, the design and the measurement of miniaturized passive and active, broadband and narrowband antennas for MF, HF and VHF frequency bands. The thesis is divided into five parts : The first part deals with a measurement system, which has been developed, validated and used for all conceived aerials. The system is based on a parallel plate cell (PPC) and allows an evaluation of the gain, the compression point, the interception point and the sensitivity using a radiative method particularly useful in the case of active integrated antennas. The second part concerns solenoidal ferrite antennas. The results obtained from electromagnetic 3D simulators were compared to the state of the art theory. Main matching technics have also been studied. The third part put the light on the possibility of development of arbitrary shaped antennas on a ferromagnetic substrate using a composite material. Two antennas developed for the VHF band, confirm this point. In the fourth part, we present a concept of antennas on a partially saturated ferromagnetic substrate. A static magnetic field associated with an initially lossy material brings up some interesting phenomena such as an increased efficiency without a degradation of the impedance matching or the directivity with very small antennas. The last part presents an application of the work across a project dedicated to long distance telecommunications in marine navigation
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Maciel, Sara Alves. "Preparação e cracterização de compósitos de CoFe2O4/ZrO2." Universidade Federal de Goiás, 2016. http://repositorio.bc.ufg.br/tede/handle/tede/5738.
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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.
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Yaya, Dagal Dari. "Conception, réalisation et caractérisation d'inductances planaires à couches magnétiques." Phd thesis, Université Jean Monnet - Saint-Etienne, 2013. http://tel.archives-ouvertes.fr/tel-00993575.
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Ce travail de thèse concerne la miniaturisation et l'intégration de composants magnétiques comme les inductances utilisées dans les convertisseurs DC-DC et les circuits haute fréquence. Cette thèse a pour objectifs : - de développer une méthodologie d'étude des inductances à couches magnétiques - de montrer la faisabilité de tels composants utilisant des couches épaisses de ferrite (50 à 500µm). Le contenu de notre document s'articule ainsi autour de trois axes : la simulation, la réalisation et la caractérisation. En simulation, le logiciel HFSS, nous a permis de concevoir, de prédire le comportement du composant et d'étudier l'influence des différents entrefers et épaisseurs du matériau magnétique. La réalisation fait appel aux différentes et nombreuses étapes micro technologiques qui sont décrites en détail. Ces étapes concernent les techniques de dépôt sous vide, les procédés de photolithographie, les techniques de dépôt électrolytique, les techniques de sciage et de collage. Enfin, la caractérisation des inductances réalisées a été effectuée en basses, moyennes et hautes fréquences respectivement au LCR mètre (20Hz à 1MHz), à l'impédance mètre (40Hz à 110MHz) et à l'analyseur vectoriel de réseaux (10MHz à 67GHz)
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Gonçalves, Lucas Fabrício. "Desenvolvimento de filmes finos multiferróicos de BiFeO3 modificadas com Ca com potencial aplicação em memórias de multiplos estados /." Guaratinguetá, 2018. http://hdl.handle.net/11449/157086.
Full textAbstract:
Orientador: Alexandre Zirpoli SimoesBanca: José Vitor Candido de Souza
Banca: Mauricio Antonio Algatti
Banca: Francisco Moura Filho
Banca: Filiberto González Garcia
Resumo: Os elementos de memórias de múltiplos estados nos quais a informação pode ser armazenada tanto nos estados de polarização quanto no estado de magnetização espontânea do elemento, podem ser obtidos, através da fabricação de filmes finos texturizados de BiFeO3 (BFO) dopados com Cálcio, sobre eletrodo de (Pt/TiO2/SiO2/Si), visando otimizar as propriedades ferroeletromagnêticas. O método Pechini ou percursores poliméricos, depositados por "Spin-Coating", é relativamente de fácil controle e baixo custo para a deposição de filmes finos texturizados. O cristal do BiFeO3 possui uma estrutura perovskita distorcida em um sistema romboédrica, mas em formato de filme fino encontramos uma fase pseudo tetragonal favorável as propriedades de memorias de múltiplos estados, como a diminuição da degradação, aumento da polarização espontânea e remanescente, diminuição na corrente de fuga, diminuição do tempo de resposta ao impulso, crescimento epitaxial, controle de vacâncias de oxigênio e diminuição de fases secundarias. Tudo isso é atingido, através de variações das resinas, controlando a volatização excessiva do Bismuto e de parâmetros no crescimento do filme, como, o tempo e temperatura de cristalização, da quantidade de dopante Ca, na variação de diferentes eletrodos óxidos de base para produção do filme fino. Apesar das excelentes propriedades dos filmes finos de BiFeO3 (BFO), dois sérios problemas são comumente encontrados para imediata aplicação deste material em memórias multiferróica... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The multi-state memory elements in which the information can be stored in both the polarization states and the spontaneous magnetization state of the element can be obtained by the production of calcium-doped thin films of BiFeO3 (BFO) on electrode (Pt / TiO2 / SiO2 / Si), in order to optimize ferroelectromagnetic properties. The Pechini method or polymer precursors, deposited by Spin-Coating, is relatively easy to control and low cost for the deposition of textured thin films. The crystal of the BiFeO3 has a perovskite structure distorted in a rhombohedral system, but in thin film format we find a pseudo tetragonal phase favorable to the properties of memories of multiple states, such as the decrease of the degradation, increase of the spontaneous and remaining polarization, decrease in the current reduction of impulse response time, epitaxial growth, control of oxygen vacancies and decrease of secondary phases. All of this is achieved through variations of the resins, controlling the excessive volatilization of Bismuth and parameters in the growth of the film, such as the time and temperature of crystallization, the amount of dopant Ca, in the variation of different base oxides electrodes for production of the thin film. Despite the excellent properties of the BiFeO3 (BFO) thin films, two serious problems are commonly encountered for the immediate application of this material in multiferroic memories: high current density, resulting in Fe (Fe3 + to Fe2 +) valence fluctuatio... (Complete abstract click electronic access below)
Doutor
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Souza, Josà Adailson de. "AvaliaÃÃo da FragilizaÃÃo a 400ÂC e a 475ÂC do AÃo InoxidÃvel FerrÃtico AISI 444 Utilizado em Torres de DestilaÃÃo de PetrÃleo." Universidade Federal do CearÃ, 2004. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7342.
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AgÃncia Nacional do PetrÃleoOs efeitos do envelhecimento a 400C e 475C na resistÃncia a corrosÃo, nas propriedades mecÃnica e magnÃtica do aÃo inoxidÃvel ferrÃtico AISI 444 foram investigados. O endurecimento causado pelo envelhecimento em ambas temperaturas foi medido, tendo sido observado que à mais intenso a 475ÂC. A susceptibilidade de corrosÃo localizada aumentou com o tempo de envelhecimento nas duas temperaturas, sendo tambÃm mais significativa a 475ÂC do que a 400ÂC. Com o tratamento de dissoluÃÃo a 570ÂC e 675ÂC ocorre a recuperaÃÃo dos valores de dureza e da resistÃncia à corrosÃo do aÃo. Diferente do aÃo inoxidÃvel duplex, o aÃo AISI 444 nÃo apresentou variaÃÃo na forÃa coercitiva e na temperatura de Curie com o aumento do tempo de envelhecimento. Os efeitos nos espectros de MÃssbauer tambÃm foram analisados.
The effects of aging at 400 C and 475 C in corrosion resistance, mechanical and magnetic properties of the ferritic stainless steel 444 were investigated. The hardening caused by aging in both temperatures was measured, it was observed that is more intense at 475 Â C. Susceptibility to localized corrosion, increased with aging time at the two temperatures, is also significantly more than 475 Â C to 400 Â C. In the treatment of dissolution at 570 Â C and 675 Â C is the recovery of hardness and corrosion resistance of steel. Unlike the duplex stainless steel, steel AISI 444 did not change in coercive force and the Curie temperature with increasing aging time. The effects in the MÃssbauer spectra were also analyzed.
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Giraud, Alexandre. "Caractérisation des matériaux magnétiques et modélisation des pertes fer dans le stator des machines électriques fonctionnant à haute fréquence." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19732/1/GIRAUD_Alexandre.pdf.
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Le travail proposé est le résultat d’une collaboration entre le Laboratoire Laplace et l’IRT SaintExupéry. Il s’inscrit dans un projet visant à améliorer l’intégration des systèmes électriques afin d’électrifier les aéronefs. Le développement de l’énergie électrique à bord des aéronefs a de nombreux avantages : gain de masse, optimisation facilitée, … Plus précisément, c’est l’utilisation des machines électriques qui est ici étudiée. Actionneur, compresseur, beaucoup de système utilisant des énergies non-électriques peuvent être remplacés par des machines électriques. Comme dans tout système de conversion d’énergie, des pertes sont présentes et ce sont les pertes magnétiques, appelées perte fer, qui sont au cœur de cette thèse. Le réseau électrique avion, ainsi que les dispositifs de commande de ces machines, induisent une large augmentation de la proportion des pertes fer par rapport aux autres pertes. Les rendements diminuent et c’est surtout leur prédiction qui pose problème : les machines électriques sont surdimensionnées par sécurité, elles deviennent moins efficaces et le gain en masse est réduit. C’est pourquoi il est indispensable d’une part de comprendre le comportement des matériaux magnétiques utilisés dans les machines électriques dans des conditions non-idéales : il s’agit de la caractérisation des matériaux magnétiques. D’autre part, il est nécessaire d’améliorer les modèles de pertes fer afin de rendre leur prédiction efficace et optimiser le dimensionnement des machines électriques. Plus leur prédiction sera précise, plus les facteurs d’influence sur les pertes seront déterminés. Il sera alors possible d’envisager une optimisation plus globale de la chaîne électromécanique. Cette thèse est une première étape vers cette intégration globale. La caractérisation des matériaux fut faite sous diverses conditions. Tout d’abord, des champs magnétiques B unidimensionnels ont été étudiés. L’influence de leur spectre sur les pertes fer était au cœur de cette caractérisation : influence de l’amplitude ou de la fréquence dans le cas de champs sinusoïdaux, puis de la fréquence et de la phase d’harmoniques dans le cas de spectre plus complexes. Les pertes fer sont très sensibles à ces paramètres, ils sont donc à prendre en compte dans le dimensionnement des machines électriques. La modélisation des pertes proposée ensuite passe par une reconstitution du cycle d’hystérésis. Il s’agit donc de prédire le champ B à partir du champ H. Basée sur le modèle Play, la modélisation quasi-statique scalaire développée a montré sa précision et sa prédictibilité. Cependant, étant scalaire et quasi-statique, ce modèle ne fonctionne pas en fréquence. Un modèle analytique de courants de Foucault ainsi que des propositions de dynamisation ont été développés. Le modèle de courants de Foucault permettrait de tenir compte des effets de fréquence et donc de compléter le modèle quasi-statique.
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Lahoubi, Mahieddine. "Structures magnétiques non colinéaires et transitions de phases dans les grenats ferrimagnétiques de terbium et d'yttrium." Grenoble 1, 1986. http://www.theses.fr/1986GRE10068.
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Determination par diffraction neutronique de la structure magnetique de tb::(3)fe::(5)o::(12) et de son evolution en fonction de la temperature de 4,2k a 650k (t::(n)=560k); analyse theorique des representation des groupes d'espace cubique ia3d rhomboedrique r**(3c) et application aux spectres de diffraction. Etude, par des mesures d'aimantation, du comportement de tb::(3)fe::(5)o::(12) et de tb::(x)y::(3-x)fe::(5)o::(12) (x=1,98; 1,0 et 0,37) en presence de champs magnetiques intenses, appliques selon les directions cristallographiques principales; mise en evidence de nombreuses transitions de reorientation de spin et determination des diagrammes de phases, entre 4,2 et 300k. Cas particulier du compose a x=0,37 qui presente une transition due a un croisement de niveaux de l'ion tb
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Roy, Debangsu. "Exchange Spring Behaviour in Magnetic Oxides." Thesis, 2012. http://hdl.handle.net/2005/3172.
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When a permanent magnet is considered for an application, the quantity that quantifies the usability of that material is the magnetic energy product (BH)max. In today’s world, rare earth transition metal permanent magnets like Nd-Fe-B, Sm-Co possesses the maximum magnetic energy product. But still for the industrial application, the ferrite permanent magnets are the primary choice over these rare transition metal magnets. Thus, in the present context, the magnetic energy product of the low cost ferrite system makes it unsuitable for the high magnetic energy application. In this regard, exchange spring magnets which combine the magnetization of the soft phase and coercivity of the hard magnetic phases become important in enhancing the magnetic energy product of the system. In this thesis, the exchange spring behaviour is reported for the first time in hard/soft oxide nanocomposites by microstructural tailoring of hard Barium Ferrite and soft Nickel Zinc Ferrite particles. We have analyzed the magnetization reversal and its correlation with the coercivity mechanism in the Ni0.8Zn0.2Fe2O4/BaFe12O19 exchange spring systems. Using this exchange spring concept, we could enhance the magnetic energy product in Iron Oxide/ Barium Calcium Ferrite nanocomposites compared to the bare hard ferrite by ~13%. The presence of the exchange interaction in this nanocomposite is confirmed by the Henkel plot. Moreover, a detailed Reitveld study, magnetization loop and corresponding variation of the magnetic energy product, Henkel plot analysis and First Order Reversal Curve analysis are performed on nanocomposites of hard Strontium Ferrite and soft Cobalt Ferrite. We have proved the exchange spring behaviour in this composite. In addition, we could successfully tailor the magnetization behaviour of the soft Cobalt Ferrite- hard Strontium Ferrite nanocomposite from non exchange spring behaviour to exchange spring behaviour, by tuning the size of the soft Cobalt Ferrite in the Cobalt Ferrite/Strontium Ferrite nanocomposite. The relative strength of the interaction governing the magnetization process in the composites has been studied using Henkel plot and First Order Reversal Curve method. The FORC method has been utilized to understand the magnetization reversal behaviour as well as the extent of the irreversible magnetization present in both the nanocomposites, having smaller and larger particle size of the Cobalt Ferrite. It has been found that for the all the studied composites, the pinning is the dominant process for magnetization reversal. The detailed structural analysis using thin film XRD, angle dependent magnetic hysteresis and remanent coercivity measurement, coercivity mechanism by micromagnetic analysis and First Order Reversal Curve analysis are performed for thin films of Strontium Ferrite which are grown on c-plane alumina using Pulsed Laser Deposition (PLD) at two different oxygen partial pressures. The magnetic easy directions of both the films lie in the out of plane direction where as the in plane direction corresponds to the magnetic hard direction. Depending on the oxygen partial pressure during deposition, the magnetization reversal changes from S-W type reversal to Kondorsky kind of reversal. Thus, the growth parameter for the Strontium Ferrite single layer which will be used further as a hard layer for realizing oxide exchange spring in oxide multilayer, is optimized. The details of the magnetic and structural properties are analyzed for Nickel Zinc Ferrite thin film grown on (100) MgAl2O4. We have obtained an epitaxial growth of Nickel Zinc Ferrite by tuning the growth parameters of PLD deposition. The ferromagnetic resonance and the angle dependent hysteresis loop suggest that, the magnetic easy direction for the soft Nickel Zinc Ferrite lie in the film plane whereas the out of plane direction is the magnetic hard direction. Using the growth condition of respective Nickel Zinc Ferrite and Strontium Ferrite, we have realized the exchange spring behaviour for the first time in the trilayer structure of SrFe12O19 (20 nm)/Ni0.8Zn0.2Fe2O4(20 nm)/ SrFe12O19 (20 nm) grown on c-plane alumina (Al2O3) using PLD. The FORC distribution for this trilayer structure shows the single switching behaviour, corresponding to the exchange spring behaviour. The reversible ridge measurement shows that the reversible and the irreversible part of the magnetizations are not coupled with each other.
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Venkatesha, N. "Nanoparticles for Bio-Imaging : Magnetic Resonance Imaging and Fluorescence Imaging." Thesis, 2015. http://etd.iisc.ernet.in/2005/3860.
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This thesis provides several nanomaterial systems that can be used as contrast agents in magnetic resonance imaging (MRI) and for optical fluorescence imaging. Nanoparticle systems described in this thesis fall under three categories: (a) graphene oxide-nanoparticle composites for MRI contrast agent application, (b) core-shell nanoparticles for MRI contrast agent
application and (c) nanoparticle systems for both MRI and optical fluorescence imaging. In the case of graphene oxide based nano-composites, the following observations were made: (i) in the case of graphene oxide-Fe3O4 nanoparticle composite, it was observed that high extent of oxidation of the graphene oxide and large spacing between the graphene oxide sheets containing Fe3O4 nanoparticles provides the optimum structure for yielding a very high transverse proton relaxivity value, (ii) in the case of graphene oxide-Gd2O3 nanoparticle composite, it was observed that this composite exhibits high value for both longitudinal and transverse relaxivity
values making it a potential materials for multi-contrast study of pathologies with a single agent,
(iii) in the case of graphene oxide-CoFe2O4 nanoparticle composites, it was observed that an increase in the reflux time of the reaction mixture containing this composite led to appreciable variations in the proton relaxivity values. Transverse relaxivity value of the water protons increased monotonically with increase in the reflux time. Whereas, the longitudinal relaxivity
value initially increased and then decreased with increase in the reflux time. In the case of coreshell nanoparticles for MRI contrast agent application two different core-shell systems were investigated. They are MnFe2O3-Fe3O4 core-shell nanoparticles and CoFe2O4-MnFe2O4 coreshell nanoparticles. Investigations of both the core-shell nanoparticle systems revealed that the
proton relaxivity value obtained in the dispersion of the core-shell nanoparticles was considerably greater than the proton relaxivity value obtained in the presence of single phase nanoparticles of the core and shell phases. Very high value of transverse relaxivity in the case core-shell nanoparticles was due to the large magnetic inhomogeneity created by the core-shell
nanoparticles in the water medium surrounding it. In the case of nanoparticle systems for both MRI and optical fluorescence imaging, two different systems were investigated. They were CoFe2O4-ZnO core-shell nanoparticles and Gd doped ZnS nanoparticles [Zn1-xGdxS, x= 0.1, 0.2 and 0.3] formed on graphene oxide sheets or coated with chitosan. In the case of CoFe2O4-ZnO core-shell nanoparticles it was observed that fluorescent CoFe2O4-ZnO core-shell nanoparticles with the unique geometry in which CoFe2O4 ferrite nanoparticles agglomerates were present
within larger sized hollow ZnO capsules yields very high value of transverse proton relaxivity when compared to the proton relaxivity value exhibited by the individual CoFe2O4-ZnO coreshell nanoparticles. In the case of Gd doped ZnS nanoparticles, two different systems were synthesized and the values of the longitudinal and transverse proton relaxivity obtained were compared. These systems were (i) graphene oxide- Zn1-xGdxS (x= 0.1, 0.2 and 0.3) nanoparticle
composites and (ii) chitosan coated Zn1-xGdxS (x= 0.1, 0.2 and 0.3) nanoparticles. It was
observed that Gd doped ZnS nanoparticles in both cases exhibit both longitudinal and transverse relaxivity values. The relaxivity values showed a clear dependence on the composition of the nanoparticles and the nanoparticle environment (presence and absence of graphene oxide). It was
also observed that Gd doped ZnS nanoparticle can be used for florescence imaging.
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Abdallah, Hafiz Mohammed Ibrahim. "Synthesis, magnetic and electrical characterizations of nanoparticle ferrites." Thesis, 2012. http://hdl.handle.net/10413/10920.
Full textAbstract:
The synthesis, structure and physical properties of a series of Mnx(Co, Mg)₁ˍxFe₂O₄,
(Mg, Sr)₀.₂ Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ (where RE are rare earth
elements) nanoferrites have been studied. These compounds were synthesized at low
reaction temperature of about 200 ⁰C using the glycol-thermal method. The starting
materials were high-purity metal chlorides or nitrates which were precipitated by
NH₄OH and KOH respectively. In addition, MnxCo₁₋xFe₂O₄ (x = 0, 0.5 and 1)
samples were produced directly from high-purity metal oxides by high-energy ball
milling technique. Single-phase cubic spinel structure and nanoparticle structure of
the synthesized samples were confirmed by X-ray diffraction (XRD) and transmission
electron microscope (TEM). The results show that the produced powders of the asprepared
samples have average grain sizes ranging from 7 to 16 nm. Filtering the
precipitates by Whatman glass microfiber filters (GF/F) appears to be important in
obtaining the small particle sizes. We suspect higher stability of the MnxCo₁₋xFe₂O₄
at x = 0 and 0.5 where complete symmetry in the proportion of the atoms on
tetrahedral (A) and octahedral (B) sites would tend to favour larger nanoparticles.
The evolutions of the magnetic properties as a function of composition, annealing
temperature under air and argon atmospheres or measuring temperature have
been investigated by ⁵⁷Fe Mössbauer spectroscopy, vibration sample magnetometer
(VSM) and superconducting quantum interference device (SQUID). Significant
changes in magnetic properties are observed across the composition ranges studied.
The Mössbauer spectra indicate ferrimagnetic, superparamagnetic and paramagnetic
behaviours of the compounds. The results show evidence of transformation
from single-domain to multi-domain structure with thermal annealing in
our samples. Temperature dependence of magnetization shows differences between
field cooling (FC) and zero field cooling (ZFC) which we attribute to spin-freezing
and thermal relaxation for typical nanoparticles. Significant increase in coercive
field with reduction in measuring temperature is obtained in Co- based compounds.
Mn₀.₅Co₀.₅Fe₂O₄, Sr₀.₂Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₂Mn₀.₁Co₀.₇Fe₂O₄ have large coercive
fields of 1.45, 3.02 and 10.70 kOe at 4 K compared to 0.17, 0.05 and 0.05 kOe
at room temperature respectively. Variation of coercive fields (Hc) with measuri
ing temperature for MnxCo₁₋xFe₂O₄ (x = 0.1 and 0.05), (Mg, Sr)₀.₂Mn₀.₁Co₀.₇Fe₂O₄
nanoferrites follow the Kneller's law for uniaxial non-interacting single domain particles
of the form Hc(T) = Hc(0)[1-( T/Tβ)α]. The observed temperature dependences
are consistent with α = 1/2. We also find evidence of the departure from this law
at lower temperature. The temperature dependence of the saturation magnetizations
were observed to vary with temperature according to the modified Bloch's
law Ms(T) = Ms(0)[1 - ( T/T₀)ᵝ] where β is at least 1.5. This is attributed to the
confinement effects of the spin-wave spectrum for magnetic clusters. The equation
appears to fit the saturation magnetization data over the entire temperature range
with values of β from 2.1 to 2.4 for the samples studied. These results are consistent
with the nanoparticle nature of the compounds.
In Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ nanoferrites, the grain sizes, lattice parameters and
saturation magnetizations increase with RE substitution which we attribute to larger
RE ions substituting smaller Fe ions. The results show evidence of superparamagnetic
behaviour of the nanoparticles. The highest grain size and magnetizations are
obtained for the Gd substituted sample. We find strong correlation between the saturation
magnetizations, grain sizes and microstrains with de Gennes factor G. The
correlation with grain sizes and microstrains appear to be unique and characteristic
of the nanoparticle nature of the compounds.
Bulk samples in the form of pellets were also produced from the as-prepared
samples of MnxCo₁₋xFe₂O₄ for resistivity measurements. The temperature dependence
of the electrical resistivity for samples sintered from 600 - 1100 ⁰C under
argon atmosphere were studied using the four-probe method from room temperature
to about 110 ⁰C. Two possible mechanisms for resistivity involving Tˉ¹ and
Tˉ¹/² dependences were investigated which we associated with semiconducting and
inter-grain conductivity respectively. The Tˉ¹/² dependence is found to fit the data
better and predicts higher activation energies. The resistivity was observed to be
sensitive to the surface of the pellet being probed and the annealing temperature.Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.
46
Yavuz, Cafer Tayyar. "Accessible and green manufacturing of magnetite (ferrous ferric oxide) nanocrystals and their use in magnetic separations." Thesis, 2008. http://hdl.handle.net/1911/22266.
Full textAbstract:
This work describes the first size dependent magnetic separation in nanoscale. Magnetite (Fe3O4) nanocrystals of high quality and uniform size were synthesized with monodispersity below 10%. Magnetite nanocrystals of 4 nm to 33 nm (average diameter) were produced. Batch synthesis was shown to go up to 20 grams which is more than 10 times of a standard nanocrystal synthesis, without loosing the quality and monodispersity. Reactor design for mass (1 gram per hour) production of magnetite nanocrystals is reported for the first time. The cost of a kg of lab purity magnetite nanocrystals was shown to be $2600. A green synthesis that utilizes rust and edible oils was developed. The cost of a kg was brought down to $22. Size dependency of magnetism was shown in nanoscale for the first time. Reversible aggregation theory was developed to explain the low field magnetic separation and solution behavior of magnetite nanocrystals. Arsenic was removed from drinking water with magnetite nanocrystals 200 times better than commercial adsorbents. Silica coating was successfully applied to enable the known silica related biotechnologies. Magnetite--silica nanoshells were functionalized with amino groups. For the first time, silver was coated on the magnetite--silica nanoshells to produce triple multishells. Anti-microbial activity of multishells is anticipated.
47
"Synthesis, structural and magnetic properties of bulk and nanosized (Zn, Cd, Cu)0.5Ni0.5Fe2o4 and NiFe204 ferrites." Thesis, 2007. http://hdl.handle.net/10413/447.
Full textAbstract:
We present a study of the synthesis, structural and magnetic properties of
bulk and nanosized (Zn, Cd, Cu)0:5Ni0:5Fe2O4 and NiFe2O4 compounds. The
e®ects of electronic con¯guration and atomic sizes of Zn, Cd, Cu and Ni on
the magnetic properties of the ferrites are the primary focus of the study.
Di®erent synthesis routes, preparation conditions and how they a®ect single
phase formation are explored.
The synthesis was undertaken by solid{state reaction, combustion, hydrothermal
and glycothermal techniques. The structure determination was by Xray
di®raction. The magnetic measurements were performed using MÄossbauer
spectroscopy (from 79 K to about 850 K) and a vibrating sample magnetometer
(at about 300 K). The bulk densities of the sintered pellets were deduced
by Archimedes principle. The bulk oxides were produced by solid{state reaction
and combustion techniques. Fine powders with grain sizes of about 10
nm were produced from bulk compounds by a Retsch planetary ball mill and
by the hydrothermal and glycothermal processes. The e®ects of the applied
pressure used to make pellets (related to green density of the raw pellets) and
the sintering temperature on the properties were investigated.
An anomalous variation of bulk densities of (Zn, Cd)0:5Ni0:5Fe2O4 oxides
with increase in pelletizing pressure was observed which appears to suggest evidence
for trapped porosity. Di®erent states of pelletizing the samples appear
to be related to a systematic change of the hyper¯ne ¯eld distributions derived
from the MÄossbauer spectra. The temperature dependence of the magnetic hyper
¯ne ¯elds at tetrahedral (A) and octahedral (B) sites were observed to vary
with temperature according to the equations Bhf (T) = Bhf (0)[1 ¡ (T=TC)n]¯n
where n = 1 (based on the Landau{Ginzburg theory) and n = 2 (based on the
Stoner theory). The equation Bhf (T) = Bhf (0)[1¡(T=TC)2]¯2 appears to ¯t the
hyper¯ne ¯eld data over a wider temperature range. The Zn{ and Cd{based
oxides were found to be ferrimagnetic with Curie temperature TC = 548 § 3 K (measured by zero velocity technique). The Cu{based compound exhibited antiferromagnetic
behavior with a magnetic transition temperature of 825 § 3 K.
The di®erence in behavior between Zn{, Cd{ and Cu{based compounds is due
to di®erence in electronic con¯guration and atomic or ionic sizes. The stronger
magnetic coupling between spins in the Cu{based sample can be explained by
the presence of RKKY interactions in addition to superexchange interactions.
The larger ionic size for Cd appears to favour smaller grain sizes in Cd{based
oxides. An anomalous increase in TC is obtained in the Zn0:5Ni0:5Fe2O4 compound
with reduction in grain size. This increase in TC is attributed to a
distribution of Zn ions on both A and B sites.
The MÄossbauer spectra of the milled nanosized samples show a combination
of ferrimagnetic and paramagnetic behavior. The coercive ¯eld (HC) at room
temperature was found to increase with reduction in grain size (G) according to
the equation HC = am+bm=G, which is consistent with multidomain particles.
With further reduction in grain sizes, the coercive ¯eld reduced according to the
equation HC = as ¡bs=G2. This equation is associated with the onset of single
domain particles. The samples produced by hydrothermal and glycothermal
processes show evidence of transformation from single domain to multidomain
structure with increasing sintering temperature.
The ease of single{phase formation in the compounds studied is shown to
depend on the technique used to prepare the samples. Single phase formation of
the spinel structure was easier to achieve in samples prepared by wet chemical
methods because lower sintering temperatures (T < 1000 oC) were required.Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2007.
48
Ming-Feng, Kuo, and 郭明峯. "High Frequency Magneto-electric Properties of Composite Material Made of Soft Magnetic Ferrites and Hard Magnetic NdFeB." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/98903625493066356424.
Full textAbstract:
碩士國立高雄師範大學
物理學系
95
The magneto-electric dynamics of composite material made of soft magnetic ferrites and hard magnetic NdFeB are studied. In this work, the nano-sized ferrites were synthesized by combustion method, and then were mixed with various amount (1, 3, 5 wt.%) of micro-sized NdFeB. The M-H behavior of the ferrites/NdFeB composites has displayed specific features of wasp-waisted hysteresis loops, correlated to the superposition of magnetization of hard and soft magnetic phases. The variation of magneto-impedance of composites has demonstrated that small amount of NdFeB additive into ferrites can significantly effect the behavior of spectra. The analysis of the impedance spectra has being done based on the classical electromagnetism, which taking into account the occurrence of dielectric relaxation and magnetic-after effect when the samples were subjected to electromagnetic field. Mechanism of hard and soft magnetic interaction underlying for the magneto-electric dynamics is investigated. The results imply for high frequency device applications utilizing ferrites/NdFeB nano-composites.
49
"Analysis, Simulation and Measurements of CBS Antennas Loaded with Non-Uniformly Biased Ferrite Material." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.14838.
Full textAbstract:
abstract: When ferrite materials are used in antenna designs, they introduce some interesting and unique performance characteristics. One of the attractive features, for example, is the ability to reconfigure the center frequency of the antenna. In addition, ferrite materials also introduce a number of challenges in the modeling and simulation of such antennas. In order for the ferrite material to be useful in an antenna design, it usually is subjected to an external magnetic field. This field induces the internal magnetic field inside the ferrite material. The internal field plays a pivotal role in the radiation characteristics of the antenna. Thus, from the numerical point of view, accurate computation of this field is critical to the overall accuracy of the analysis. Usually the internal field is non-uniform and its computation is often a rather complex and non-trivial task. Therefore, to facilitate the modeling, simplifying assumptions, which introduce some kind of averaging, are often made. In this study, ferrite-loaded cavity-backed slot antennas are used to demonstrate that averaging procedures can lead to very unsatisfactory results. For instance, it is common practice to assume that the external field is uniform by averaging its distribution. One of the pivotal points in this study is the demonstration that the external magnetic field plays a very significant role and should be included in the modeling without averaging, if the accurate results are to be attained. Results presented in this study clearly support this argument. A procedure which avoids such averaging is presented and verified by comparing simulations with measurements. In contrast to the previous formulations, the modeling methodology developed in this dissertation leads to accurate results which compare very well with measurements for both uniform and non-uniform field distributions. The utility of this methodology is especially evident for the case when the magnetic field is severely non-uniform.Dissertation/Thesis
Ph.D. Electrical Engineering 2012
50
Msomi, Justice Zakhele. "Mossbauer spectroscopy and x-ray diffraction study of (Cd, Zn) substituted mixed ferrites." Thesis, 2002. http://hdl.handle.net/10413/4412.
Full textAbstract:
The study of magnetic properties and structures of Zn and Cd substituted
mixed ferrites has been carried out using Mossbauer spectroscopy and X-ray
diffraction on powdered samples at about 300 K. Two series of mixed ferrites,
(Cd, Zn)xCol-xFe2-xAlxO4 and (Cd, Zn)xCo0.9Fe1.7-xTi0.4O 4 (where 0≤ x≤1.0)
were synthesized. In the former series the effect of simultaneous site dilution
by Zn or Cd and Ai atoms on tetrahedral (A) and octahedral (B) sites is investigated
and in the latter the effect of single site dilution by Zn or Cd is also
studied. The Mossbauer spectra show that the compounds transform with increase
in x from ordered to disordered magnetic states. Systematic decrease
in the hyperfine fields indicating weakening of the magnetic coupling with an
increase in x is observed. We report the presence of a cross over effect with
respect to the hyperfine fields on A and B sites at low concentration of diamagnetic
ions in the simultaneously diluted series. Both series of compounds show
no significant changes in isomer shifts with x. Differences in the evolution of
Fe atoms on A and B sites between Zn and Cd based compounds are observed.
The results of our analysis show that Zn and Cd ions occupy both tetrahedral
and octahedral sites. The spinel structure of the compounds studied in this
work is confirmed by X-ray diffraction (XRD). The lattice parameters derived
from XRD show systematic change with x consistent with Vergard's law. In
Cd based samples an increase of the lattice parameter with x is explained on
the basis of the size difference of the cations involved. However, an anomalous
behavior of the lattice parameter is observed in Zn based samples. The
average grain sizes of the samples were determined from the line width of the
(311) XRD intensity lines using the Scherrer formula. These vary between 50
nm and 70 nm for all the samples except for Zn and Al substituted samples
which show a systematic anomalous reduction for x ≥ 0.4 in grain size. The
porosity, x-ray and bulk densities of the samples are also presented.Thesis (M.Sc.)-University of Natal, Durban, 2002.