Banca de QUALIFICAÇÃO: JULIANA GONÇALVES DIAS

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : JULIANA GONÇALVES DIAS
DATE: 28/04/2023
TIME: 14:00
LOCAL: Bloco B Sala 303
TITLE:

Synthesis and Characterization of the Structural and Physical Properties of the R3Co4Ge13 Series Compounds

PAGES: 50
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUBÁREA: Física da Matéria Condensada
SUMMARY:

The intermetallic family of ternary compounds with the general formula R3T4X13(R = rare
earth, T = transition metal, X = Ge, Sn) crystallizes in a complex cubic structure with an
atomic arrangement that categorizes them as cage compounds. The effects related to this
structural complexity make this family an object of broad interest for understanding and
applications of various physical phenomena. In this context, the main goals of this work
were to produce single crystals of some of the series rare earth members R3Co4Ge13(R =
Y, Gd, Tb, Dy, Ho, Er, Tm, Yb e Lu) and perform basic characterizations. Single crystals
were grown by the self-flux method using excess Ge and had their structural characteristics
probed through X-ray powder diffraction at room temperature. Rietveld refinement analysis
established that the samples crystallize in the cubic structure with space groupPm3n.
Except for the Yb member, the room temperature lattice parameter decreases as a function
of rare earth atomic number, which is consistent with the decrease of the ionic radius of the
trivalent rare earth ions along the series, a phenomenon known as lanthanide contraction.
Temperature-dependent specific heat and magnetization measurements were performed
in the temperature range 2 K≤T≤300 K. The specific heat measurements revealed
a lambda-like anomaly for the Gd, Tb, and Dy members, suggesting a phase transition
confirmed as antiferromagnetic by magnetization measurements. The Ho, Er, and Tm
compounds show Curie-Weiss type behavior. The Y and Lu are non-magnetic compounds,
whereas Yb reveals typical valence fluctuation behavior in magnetic susceptibility analysis.
The ordering temperatures for Gd, Tb, and Dy scale with the de Gennes factor, with
evidence that the coupling between the local4fmoments is mediated by indirect RKKY
interactions. Our study of this series of compounds gathers systematic results that allow
us to advance with new perspectives of doping and substitutions, aiming to explore other
physical phenomena.

COMMITTEE MEMBERS:
Presidente - Interno ao Programa - 2605463 - JOSE ANTONIO SOUZA
Membro Titular - Examinador(a) Interno ao Programa - 1734908 - FABIO FURLAN FERREIRA
Membro Titular - Examinador(a) Interno ao Programa - 3944999 - ROMARLY FERNANDES DA COSTA
Membro Suplente - Examinador(a) Interno ao Programa - 2249395 - THIAGO BRANQUINHO DE QUEIROZ