Banca de DEFESA: SILAS SARMENTO PEDROSA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : SILAS SARMENTO PEDROSA
DATA : 15/09/2017
HORA: 15:30
LOCAL: Auditório do DFTE
TÍTULO:

Dipolar effects on the magnetic phases of superparamagnetic clusters

PALAVRAS-CHAVES:

Superparamagnetic nanoparticles, initial magnetic susceptibility, magnetic
nanoparticles clusters, dipolar interactions.

PÁGINAS: 130
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
RESUMO:

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 9nm to 12nm, 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.

MEMBROS DA BANCA:
Externo à Instituição - ANA LUCIA DANTAS - UERN
Presidente - 6345702 - ARTUR DA SILVA CARRICO
Externo à Instituição - GUSTAVO DE OLIVEIRA GURGEL REBOUCAS - UFERSA
Interno - 350830 - JOSE HUMBERTO DE ARAUJO
Interno - 1675199 - SUZANA NOBREGA DE MEDEIROS