Banca de DEFESA: MARCELO FRANCIS FERNANDES ALECRIM

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : MARCELO FRANCIS FERNANDES ALECRIM
DATE: 22/03/2024
TIME: 14:00
LOCAL: Google Meet - Online
TITLE:

"Synthesis, structural characterization and magnetic properties of the compounds (Gd1-xFex)2CuO4"

 

KEY WORDS:

Magnetic Materials and Magnetic Properties; Magnetocaloric Effect; Model of Magnetic Sub-lattices.

 

 

PAGES: 76
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUBÁREA: Física da Matéria Condensada
SPECIALTY: Materiais Magnéticos e Propriedades Magnéticas
SUMMARY:

Polycristalline samples following the nominal formula (Gd1−xF ex)2CuO4 with x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 0.9 and 1.0 were prepared by solid state reaction at ambient atmosphere using high-purity Gd2O3, F e2O3 and CuO oxides. Samples of an approximatelly one gram were mixed and pressed into pellets of 10 mm of diameter using 6 Tons of pressure. The samples were sintered three times at 960 C/48 h and between each process they were grinded a pelleted again. In order to investigated the coexistence of magnetic phases in the samples were performed X-ray diffraction and 57Co Mössbauer spectroscopy experiments. XRD Rietveld refinement analysis in x = 0 reveals that this sample growthed in pure I4/mmm tetragonal Gd2CuO4 phase that is antiferromagnetic (AFM). For x = 0.2 and 0.4 the coexistence of the (AFM) tetragonal I4/mmm Gd2CuO4 and the (AFM) Pbmn orthorrombic GdF eO3 phases was observed; for x = 0.5 the sample shows only the (AFM) orthorrombic Pbmn GdF eO3 phase; for x = 0.6 occurs the coexistence of (AFM) Pbmn GdF eO3 and cubic ferrimagnetic (FI) Ia-3d Gd3F e5O12; for x = 0.8 and 0.9 the coexistence of the (FI) Ia-3d Gd3F e5O12 and the (FI) I41/amd:2 F e2CuO4; and finally, for x = 1 was obtained the (FI) I41/amd:2 tetragonal F e2CuO4 phase. Nominal stoichiometry permit us to estimated the relative quantity of each phases in each sample. Additionally, magnetization measurements as a function of magnetic field and temperature were performed in the samples. The magnetic properties of each phase for each the compounds were calculated using a Hamiltonian that contains the exchange interaction between magnetic sublattices formed by Gd-Fe, Fe-Fe and Gd-Gd ions and the Zeeman term, where it was considered as the total magnetic response the sum of the responds of each magnetic phase. In the coexistence of iron magnetic crystallographic sites the relative intensities between the corresponding hyperfine fields were used to improve the computational simulations. Furthermore, good agreement was found in the magnetization response and in the variation of magnetic entropy as a function of temperature and applied magnetic field, calculated from experimental magnetization measurements and from computational simulations. This methodology permit us to verify the amounts of each magnetic phase in each sample founded previously by nominal stoichiometry, XRD and Mössbauer measurements with good accuracy and from hyperfine field data and computational calculations the exchange parameters for each magnetic phase were obtained. Interpolating the experimental values of x and the relative quantities of the magnetic phases it is possible to construct a phase diagram that permits guide to preparing samples with two specific magnetic phases in any desire rate in order to prepared in a one only process composites to applications in the design of thermomagnetic devices.

 

 

BANKING MEMBERS:
Presidente - 1719870 - JUAN CARLOS PAREDES CAMPOY
Interno - 1527524 - WAGNER SOUZA MACHADO
Externo à Instituição - EDUARDO GRANADO MONTEIRO DA SILVA - UNICAMP
Externo à Instituição - EDISON JESUS RAMIREZ PLAZA - SS340