Banca de QUALIFICAÇÃO: ÁLISON PEREIRA DA SILVA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : ÁLISON PEREIRA DA SILVA
DATA : 11/12/2023
HORA: 08:30
LOCAL: videoconferência
TÍTULO:

Synthesis and Study of Physical Properties of Anisotropic MnFe2O4−SiO2 Composites Obtained via Solid State Reaction Using Minerals

PALAVRAS-CHAVES:

Composites. Manganese ferrites. Anisotropy. State reaction
solid. Minerals.

PÁGINAS: 50
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Materiais Magnéticos e Propriedades Magnéticas
RESUMO:

Microstructure governs the magnetic performance of different groups of materials. Most magnetic materials crystallize in nearly isotropic structures and forms. On the other hand, it is estimated that better sample alignment can be obtained if preparation conditions are improved. A special advantage of anisotropic crystals lies in their direction-dependent behavior, since they are sensitive to the direction of applied magnetic fields, and are not limited only to magnetic properties, but are also reflected in other functionalities such as electrical, optical and chemical. Anisotropic MnFe2O4-SiO2 composites, in the form of powders and tablets, were obtained by the solid state reaction method, synthesized at a temperature of 1200oC/12h under ambient atmosphere, from fresh minerals extracted in the state of RN – Brazil. In view of this, three powder samples were subjected to the influence of magnetic fields of ∼0.25T, ∼0.50T, ∼1T and one without the influence of a magnetic field, which were compacted in a pelletizer applying a fixed pressure of 370MPa. The study in question addresses the alignment and influence of magnetic fields on the crystalline/morphological structure of sintered tablets, analyzing their changes in the magnetic ordering and physical-chemical properties of the samples. The microstructures/morphologies of the samples were investigated using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively, to understand the effect of the vectorization process on the magnetic properties, particle sizes and morphology. Clusters of triangular crystals were obtained with more regular edges and superficially porous crystallites in the series of tablets. Possibly its triangular predominance comes from the anisotropy of shape, through the presence of domain walls, with thickness as the main parameter. The crystallites gained a degree of crystallinity, sharpness and partial orientation resulting from the alignment of magnetic fields. Magnetic properties were measured using a Vibrating Sample Magnetometer (VSM). By turning 30 degrees, we measure the necessary angles (0 to 330 degrees) for comparison studies to identify the easy and rigid magnetization axis. The magnetic measurements showed that there is no axis of anisotropy, that is, a preferential direction of magnetization in X and Y when the pellets were rotated parallel to the applied magnetic field. However, there is anisotropy arising from the vectorization fields when the pads were oriented perpendicularly in relation to the plane, presenting different initial susceptibility curves, based on variations in the Z axis.

MEMBROS DA BANCA:
Presidente - 1881 - VAMBERTO DIAS DE MELLO
Externo à Instituição - MARCELO ANDRADE MACÊDO - UFS
Externo à Instituição - ISAAC BARROS TAVARES DA SILVA - UFERSA