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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.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/24673 |
| Date | 15 September 2017 |
| Creators | Pedrosa, Silas Sarmento |
| Contributors | 33014019704, Dantas, Ana L?cia, 78604303472, Rebou?as, Gustavo de Oliveira Gurgel, 03574307438, Ara?jo, Jos? Humberto de, 24150720444, Medeiros, Suzana N?brega de, 78609801420, Carri?o, Artur da Silva |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM F?SICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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