Banca de DEFESA: MARCOS SANTOS NUNES

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : MARCOS SANTOS NUNES
DATE: 23/02/2024
TIME: 10:00
LOCAL: Plataforma Google Meet
TITLE:

Study of Ferrite Nanoparticles for Potential Applications in Permanent Magnets and Magnetic Hyperthermia: Analysis of
Magnetic and Structural Properties.

KEY WORDS:

Nanoparticles, Core@Shell, 𝐶𝑜𝐹𝑒2𝑂4@𝐶𝑜𝐹𝑒2, Exchange Coupling, Chitosan, Manganese Ferrite, SLP (Specific
Loss Power), Superparamagnetic, Magnetic Hyperthermia

PAGES: 120
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

The quest to enhance magnetic properties through core@shell nanoparticles and the investigation of the heating effect
of magnetic nanoparticles using an alternating magnetic field have sparked intense scientific and technological interest.
Significant advancements in this field have been driven by progress in the production techniques of nanoscale magnetic
materials, enabling diverse applications such as permanent magnets, biomedical applications, and magnetic hyperthermia. This
thesis addresses two distinct nanostructured systems. The first focuses on the synthesis of 𝐶𝑜𝐹𝑒2𝑂4@𝐶𝑜𝐹𝑒2 nanocomposites
with core@shell structure using a method that does not involve special reagents or gases. The process involved the preparation
of glutaraldehyde-crosslinked chitosan beads containing 𝐶𝑜𝐹𝑒2𝑂4 nanoparticles, followed by high-temperature and vacuum
thermal treatment. The CO gas released during this process facilitated the reduction of 𝐹𝑒3+and 𝐶𝑜2+ ions to their zero-valent
states. After the synthesis, the structural, morphological, and magnetic properties of the samples were investigated. X-ray
diffraction analysis, transmission electron microscopy (TEM), and Mössbauer spectroscopy revealed the presence of the desired
magnetic phases. TEM images confirmed the core@shell structure. Magnetic characterization indicated exchange-coupling
between the phases under certain synthesis conditions, resulting in a maximum energy product (𝐵𝐻)𝑚𝑎𝑥= 0.67 MGOe. The
thickness of the CoFe$_2$ phase (≈ 9.0 nm) aligns with the theoretical limit expected by the Kneller-Hawig theory, which is
10.2 nm, for exchange coupling at the interface. The second system involves the synthesis and study of the magnetic properties
of Manganese Ferrite 𝑀𝑛𝐹𝑒2𝑂4 nanoparticles. In this part of the work, 𝑀𝑛𝐹𝑒2𝑂4 nanoparticles were synthesized using the
same method as the previous system but with conventional thermal treatment in the presence of air. Samples with various sizes
were obtained by thermal treatments at different temperatures, resulting in particle sizes ranging from 7.8 to 13.3 nm. At 300 K,
the saturation magnetization of the nanoparticles varied from 16.2 to 35.8 emu/g. Low-temperature Mössbauer spectroscopy
showed the presence of monophasic 𝑀𝑛𝐹𝑒2𝑂4. For all samples, the Mössbauer results at 300 K suggested superparamagnetic
behavior. AC and DC susceptibility measurements indicated that below the blocking temperature, the system behaves as a
superspin glass. Specific Loss Power (SLP) measurements were conducted at a frequency of 74 kHz and AC field amplitude of
247 Oe. The sample thermally treated at 600 °C, with a dispersion prepared at a concentration of 1.0 mg/mL, exhibited the
highest SLP of 129.1 W/g.

COMMITTEE MEMBERS:
Externa à Instituição - ANA LUCIA DANTAS - UERN
Externo ao Programa - 3309102 - ANDREA PAESANO JUNIOR - nullInterno - 1508681 - FELIPE BOHN
Presidente - 350830 - JOSE HUMBERTO DE ARAUJO
Externo à Instituição - JOÃO MARIA SOARES - UERN
Interno - 1674707 - MARCO ANTONIO MORALES TORRES