Banca de QUALIFICAÇÃO: LEONARDO SOARES DE OLIVEIRA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : LEONARDO SOARES DE OLIVEIRA
DATA : 05/03/2020
HORA: 14:00
LOCAL: Santo Andre
TÍTULO:

Structural, electronic, and magnetic properties of (Nd, Pr)₂CoFeO₆ as new disordered double perovskite compounds

PÁGINAS: 60
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Materiais Magnéticos e Propriedades Magnéticas
RESUMO:

The structural, magnetic, and electronic properties of new disordered (Nd,Pr)₂CoFeO₆ double perovskite compounds have been investigated. The compounds were successfully obtained by solid-state reaction method at 1573 K in air. The XRD patterns indicate the growth of a single phase with high crystallinity without traces of impurities. Rietveld refinement of (Nd,Pr)₂CoFeO₆ indicates that both compounds crystallize in the orthorhombic Pnma space group symmetry with the BO₆ octahedral half occupied with Co and Fe ions at 4b Wyckoff site. High temperature XRD patterns reveal the absence of a structural phase transition. The magnetic characterization of both compounds indicates a predominance of strong AFM ordering with critical temperature around 250 K. Above this temperature and up to 380 K, it was observed that the χ^-1(T) does not follow the Curie-Weiss law for the paramagnetic state. A downturn deviation χ^-1(T) indicates the presence of magnetic short-range order within a paramagnetic matrix, also discussed here as Griffiths-like phase. The presence of this phase was confirmed by the signatures in the modified Currie-Weiss law and in the isothermal remanent magnetization. To date, just a few AFM compounds have been reported to exhibit Griffiths-like phase. AC electrical transport shows that the compounds behave as a semiconductor until a crossover to the metallic-like state is observed. It is suggested that the temperature of this critical variation on the electric resistivity is lowered as the atomic radii decreases. Also, as the temperature increases, it is observed a change from the capacitive to an inductive nearly in the same temperature interval where the system reaches the conventional paramagnetic state. The aim of this work is to elucidate the complex magnetic, transport, and structural properties of these new disordered double perovskite compounds.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1734908 - FABIO FURLAN FERREIRA
Membro Titular - Examinador(a) Interno ao Programa - 1545089 - DANIEL ZANETTI DE FLORIO
Membro Titular - Examinador(a) Externo ao Programa - 1671599 - MARCOS DE ABREU AVILA
Membro Titular - Examinador(a) Externo ao Programa - 3066318 - JULIAN ANDRES MUNEVAR CAGIGAS
Membro Suplente - Examinador(a) Interno ao Programa - 1544408 - GUSTAVO MARTINI DALPIAN
Membro Suplente - Examinador(a) Interno ao Programa - 1707133 - ISELI LOURENCO NANTES CARDOSO
Membro Suplente - Examinador(a) Interno ao Programa - 1957564 - CEDRIC ROCHA LEAO
Membro Suplente - Examinador(a) Interno ao Programa - 2946001 - ANTONIO ALVARO RANHA NEVES