Banca de DEFESA: LUCAS MARQUES DA SILVA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : LUCAS MARQUES DA SILVA
DATE: 01/07/2022
TIME: 10:00
LOCAL: PROIN
TITLE:

Study of the influence of doping and coupling of magnetic phases on the (BH)_max of BaFe₁₂O₁₉

KEY WORDS:

barium hexaferrite, doping, cobalt ferrite, cobalt iron alloy, nanocomposites, exchange-spring coupling, exchange interactions, dipolar interactions, Henkel plots, energy product.

PAGES: 149
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

The M-type barium hexaferrite (BaFe₁₂O₁₉), an iron oxide with hexagonal geometry, is a material that play an important technological role in applications such as permanente magnets, microwave devices and magnetic recording. In this work, we study the influence of two experimental approaches used to improve the maximum energy product, (BH)_max, of barium hexaferrite: doping with lanthanum (La) and cobalt (Co), and the coupling of magnetic phases. In the first one, we produced samples of barium hexaferrite, using the Ionic Coordination Reaction (ICR) method, doped with a fixed amount of La and a variable amount of cobalt, Ba_0.7La_0.3Fe_12-xCo_xO₁₉, x = (0.0, 0.25, 0.50, 0.75 and 1.0). In the second, through the polyol process, we coated samples of pure and impurity-free barium hexaferrite (also obtained by the ICR method) with superparamagnetic nanoparticles of cobalt ferrite (CoFe₂O₄), obtaining coupled nanocomposites of BaFe₁₂O₁₉/CoFe₂O₄ with

different proportions. Then, these samples were submitted to a reductive process in a hydrogen atmosphere, where there was a partial reduction of cobalt ferrite, giving rise to a new nanocomposite of the BaFe₁₂O₁₉/CoFe₂O₄@CoFe₂ type. These samples were characterized by the use of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), as a function of magnetic field and temperature and Mössbauer spectroscopy. In the first approach, XRD measurements showed the presence of a small amount of α-Fe₂O₃ in the doped samples. The SEM images revealed a morphology like nanorod, smaller than the critical limit for single-domain particles. Optimized magnetic properties were achieved for the sample with concentration of Co x = 0.25. Furthermore, this sample displayed the highest value of (BH)_max of 6.98 kJ/m³ (0.877 MGOe), which corresponds to a significant improvement of 8% over the pure sample. For the second approach, XRD analyzis revealed the presence of two phases, BaFe₁₂O₁₉ and CoFe₂O₄, for the as prepared nanocomposites, and three phases, BaFe₁₂O₁₉, CoFe₂O₄ and CoFe₂, for the nanocomposites after reduction. The TEM micrographs showed that the different phases are structurally coupled. Magnetization (M_r) and remanent demagnetization (M_d) measurements were performed at room temperature. Through M_r and M_d it was possible to make the Henkel and δm plots of the nanocomposites that provided information about the nature of the interactions between the phases and about the magnetic behavior. We detected a coupling of the exchange-spring type between the phases of the nanocomposites.

BANKING MEMBERS:
Presidente - 350830 - JOSE HUMBERTO DE ARAUJO
Interno - 1508681 - FELIPE BOHN
Interno - 1674707 - MARCO ANTONIO MORALES TORRES
Externo à Instituição - JOSÉ FERNANDO MORAIS LOPES MARIANO - UdA
Externo à Instituição - ANDREA PAESANO JÚNIOR - UEM