Banca de DEFESA: DIEGO ALVES DE BARROS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : DIEGO ALVES DE BARROS
DATE: 25/03/2020
TIME: 10:30
LOCAL: Auditório do DFTE
TITLE:

Synthesis and Characterization of NdCo Magnetic Nanostructures Covered with PVP

KEY WORDS:

Permanent magnets, polyol method, PVP, rare earth, transition metals.

PAGES: 88
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Rare earth (RE) intermetallic compounds and transition metals (TM) are widely used in the production of permanent magnets and have, in general, ferromagnetic behavior. Most of these compounds are produced in an arc furnace or in ball mills, physical methods that do not allow controlling many variables in the process. Currently, much of the research in this area is related to the production of these compounds through chemical methods. In this work, we propose a process for the synthesis of magnetic nanoparticles of the NdCo type via the polyol method, with the use of PVP, for five samples with variation in the molar proportions of the compounds. PVP was used to protect the particles against aggregation and oxidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements were performed for structural and morphological analysis, respectively. DC magnetization measurements, vibrant sample magnetometry at 5 K and 300 K and magnetic thermogravimetry (MTG), were performed for magnetic characterization. The XRD measurements showed the formation of the NdCo₂, Nd₂Co₇, Nd₅Co₁₉ and Nd₂Co₁₇ phases, with predominance of the Nd₂Co₁₇ phase, for four of the five samples, for four of the five samples. The diffractogram network parameters were obtained through the rietveld refinement and showed that the average crystallite sizes ranged from 6.5 nm to 20.7 nm. Through TEM it was possible to observe ellipsoidal and spherical nanoparticles, distributed in a PVP matrix, with size distributions ranging from 6.1 nm to 12.4 nm, and which crystallographic planes and their respective phases contributed to the formation of the images. The DC magnetization measurements as a function of temperature indicated the Curie temperatures (Tc) of the phases and are in accordance with the literature and XRD measurements, the magnetization values showed elevations in the vicinity of Tc which are related to the PVP phase shift to high temperatures, and the consequent formation of metastable phases, rich in Cobalt, reported in the literature. The ferromagnetic behavior was observed in all samples at both 5 K and 300 K in the measurements of magnetometry of vibrant sample. With the TGM magnetic thermogravimetry measurements, the transition temperatures for the phases reported in the previous measurements were obtained, including for the metastable phases, through the simple interpolation method.

BANKING MEMBERS:
Presidente - 350830 - JOSE HUMBERTO DE ARAUJO
Interno - 6346140 - LUCIANO RODRIGUES DA SILVA
Externo à Instituição - LÁZARO LUIS DE LIMA SOUSA - UFERSA
Interno - 1674707 - MARCO ANTONIO MORALES TORRES
Externo ao Programa - 050.025.724-80 - RODOLFO BEZERRA DA SILVA - UERN
Externo à Instituição - THOMAS DUMELOW - UERN