Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2018-01-24T12:09:54Z No. of bitstreams: 1 SilasSarmentoPedrosa_TESE.pdf: 13307553 bytes, checksum: 616db20e12e34747afe3ca24c303b31a (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2018-01-26T12:09:55Z (GMT) No. of bitstreams: 1 SilasSarmentoPedrosa_TESE.pdf: 13307553 bytes, checksum: 616db20e12e34747afe3ca24c303b31a (MD5) / Made available in DSpace on 2018-01-26T12:09:55Z (GMT). No. of bitstreams: 1 SilasSarmentoPedrosa_TESE.pdf: 13307553 bytes, checksum: 616db20e12e34747afe3ca24c303b31a (MD5) Previous issue date: 2017-09-15 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / H? presentemente grande interesse de pesquisa em aglomerados de nanopart?culas superparamagn?ticas, devido em parte ? alta demanda para aplica??es biom?dicas, e ao mesmo tempo ao grande interesse, do ponto de vista fundamental, em novas fases magn?ticas. A suscetibilidade magn?tica inicial e o campo de fuga, s?o fatores essenciais para otimiza??o de sistemas para aplica??es biom?dicas. H?, ao mesmo tempo, grande interesse em confirmar a exist?ncia de ferromagnetismo dipolar, em sistemas onde a energia de troca n?o ? fator dominante. Desenvolvemos um estudo te?rico do impacto da intera??o dipolar sobre as fases magn?ticas de nanopart?culas superparamagn?ticas, confinadas em aglomerados esf?ricos e elipsoidais. Consideramos nanopart?culas de Fe3O4 com tamanhos no intervalo de 9 nm a 12 nm, arranjadas com densidade uniforme em aglomerados de tamanho da ordem de centenas de nan?metros. Mostramos que as fases magn?ticas, e a suscetibilidade inicial, s?o controladas pela intera??o dipolar, e que a topologia do arranjo de nanopart?culas, o tamanho das nanopart?culas e a densidade de empacotamento s?o fatores que controlam as propriedades magn?ticas. Mostramos que a intera??o dipolar pode estabilizar fases magn?ticas cl?ssicas, conhecidas apenas para sistemas com alto conte?do de energia de troca e de anisotropia. Al?m disso, as fases magn?ticas em reman?ncia t?m uma caracter?stica peculiar: a m?dia t?rmica do momento de cada nanopart?cula pode se aproximar do valor de satura??o, mantendo o aglomerado superparamagn?tico. Aglomerados elipsoidais de alta excentricidade s?o os sistemas de escolha para aplica??es biom?dicas porque podem exibir expressivo aumento de suscetibilidade magn?tica, mantendo um campo de fuga de baixa intensidade em reman?ncia. O modelo te?rico reproduz satisfatoriamente resultados experimentais de aglomerados esf?ricos de Fe3O4, e de sistemas de part?culas de Fe e Co de baixa dimensionalidade. / Superparamagnetic nanoparticles clusters are currently driving considerable research attention. The interest stems from chances of designing systems with promising potential for technological applications, and from the fundamental viewpoint, tailoring new magnetic phases. The initial magnetic susceptibility and the stray field, at remanence, are key features for the optimization of magnetic systems for biomedical applications. Also, the existence of dipolar ferromagnetism, in the absence of exchange energy, has been one of the focus of magnetism for decades. We report a theoretical discussion of the impact of the dipolar interactions on the magnetic phases of superparamagnetic nanoparticles confined in spherical and ellipsoidal clusters. We consider Fe3O4 nanoparticles, with size ranging from 9 nm to 12 nm, arranged with uniform density in hundreds nanometer size volumes. We show that the magnetic phases, and the initial susceptibility, are controlled by the dipolar interaction. Also, the topological nanoparticle arrangement, the nanoparticle size, and the packing density, are key features. We show that the dipolar interaction alone may stabilize classical magnetic phases, well known for systems with large content of exchange and anisotropy energies. In addition, we have found that at remanence the nanoparticles clusters magnetic phase have a unique property. The dipolar energy leads to thermal stabilization of the individual nanoparticles moments. Large nanoparticles densities may allow nearly full thermal value of the nanoparticles magnetic moments. Despite this, the nanoparticles cluster is superparamagnetic, with a rather small stray field at remanence, as required for biomedical safety. Nanoparticle clustering in large eccentricity ellipsoidal volumes are promising systems for both low field and large field biomedical applications. For low field applications, there is a large increase in the initial susceptibility, with enhancement in the efficacy of vector targeting and also for hyperthermia absorption rate. For high field applications, the enhancement of the stray is much stronger than that for spherical clusters. Our theoretical model reproduces typical properties of Fe3O4 nanoparticles spherical clusters, as well as intriguing results for Fe and Co quasi-one-dimensional systems.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-03-09T19:50:48Z No. of bitstreams: 1 LeonardoLinharesOliveira_TESE.pdf: 68488662 bytes, checksum: de2543920cd8d7f953cc8b1b5d1ebf66 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-03-13T19:10:14Z (GMT) No. of bitstreams: 1 LeonardoLinharesOliveira_TESE.pdf: 68488662 bytes, checksum: de2543920cd8d7f953cc8b1b5d1ebf66 (MD5) / Made available in DSpace on 2017-03-13T19:10:14Z (GMT). No. of bitstreams: 1 LeonardoLinharesOliveira_TESE.pdf: 68488662 bytes, checksum: de2543920cd8d7f953cc8b1b5d1ebf66 (MD5) Previous issue date: 2016-06-23 / Nanopart?culas bi-magn?ticas t?m se mostrado promissores em v?rias aplica??es tecnol?gicas, tais como produ??o de ?m?s permanentes, desenvolvimento de geradores de micro-ondas, nano osciladores e sistemas para grava??o magn?tica. Apresentamos um estudo te?rico acerca de nanoestruturas bimagn?ticas do tipo n?cleo@casca constitu?da de materiais ferromagn?ticos de alta e baixa anisotropia. O presente trabalho analisou nanopart?culas com geometria esf?rica e cil?ndrica. Part?culas com formato esf?rico pode ser empregada como pe?a fundamental na constru??o de im?s permanentes de alto desempenho, pois podem apresentar melhorias expressivas no produto energ?tico m?ximo, (BH)max, do sistema. O (BH)max ? um par?metro chave, pois determina se um material ? considerado bom para im? permanente. Nossos resultados mostram que o (BH)max pode ser melhorado significativamente, uma part?cula SmCo5 com 3,5 nm de di?metro recoberta por uma casca de Ferro de 2,5 nm de espessura pode apresentar (BH)max cerca de 4 vezes maior que a part?cula n?o recoberta. No entanto, para um n?cleo de mesmo material, com di?metro muito superior e cascas de Ferro relativamente espessas h? uma redu??o do (BH)max que inviabiliza seu uso para a fabrica??o de ?m?s permanentes. Discutiremos nesse trabalho o comportamento do produto energ?tico destes sistemas. Nanoestruturas com geometria cil?ndrica apresentam diversas aplica??es, como nano osciladores e mem?rias magn?ticas. Dessa forma, conhecer o perfil magn?tico e o comportamento da magnetiza??o no processo de desmagnetiza??o ? de grande relev?ncia. Um cilindro de Permalloy pode com di?metro de 57,0 nm e altura de 21,0 nm apresentar ao longo de sua curva de magnetiza??o o estado v?rtice. A inibi??o deste estado ? relevante para algumas aplica??es e pode ser alcan?ada com a presen?a de um anel externo de um material com momento magn?tico elevado. Do mesmo modo, pode apresentar v?rtice na curva de magnetiza??o devido a presen?a do anel magn?tico. Estudamos ainda os estados magn?ticos presentes em an?is devido a intera??o magn?tica dipolar com o n?cleo. / Bi-magnetic anoparticles has been shown promises in several tachnological applications, such that permanent magnets, microwave generators devices, nanooscilators and magnetic record system for example. We presents a theoretical study about bi-magnetic core@shell nanoparticles consisting of high and low anisotropy ferromagnetic materials. The present work has analyzed nanoparticles with spherical and cylindrical geometries. Spherical particles can be employed as building block for high performance magnets, because can presents a expensive improvement in high energy product, (BH)max, of the system. The (BH)max is a key parameter, because it?s indicate if a material is good to permanent magnets. Our results show that (BH)maxcan be improved significantly, a particle of SmCo5 with 3.5 nm recovered by iron shell with 2.5 nm thickness can presents (BH)max thereabout 4 times great then uncovered particle. In other way, a core of the same material, with major diameter s relative thick shell there is a reduction in (BH)max that unfeasible their use in production of permanent magnets. We discuss in the present work the behavior of energy product these systems. Nanostructures with cylindrical geometries presents several applications, such that nano-oscillators and magnetic memory. In this way, know the magnetic profile and behavior of magnetization in demagnetizing process is relevant. A permalloy cylinder can, with 57.0 nm diameter and 21.0 nm height, presents along your magnetization curve, a vortex state. The inhibition of this state is relevant for some applications and can be reached with a presence of an external ring with elevated magnetic moment material. In the same way, can present vortex in magnetization curve by magnetic ring presence. We study further the magnetic states existing in magnetic ring due to magnetic dipolar interaction with a core.