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[‹‹]VOLTAR
Transition from cooperative to non-cooperative Jahn-Teller distortion in multiferroic rare-earth manganites
Tutor/Responsável: JOAQUIM AGOSTINHO GOMES MOREIRA
Instituição: INSTITUTO DE FÍSICA DOS MATERIAIS DA UNIVERSIDADE DO PORTO (IFIMUP)
Local: IFIMUP
Área: FÍSICA DA MATÉRIA CONDENSADA
Ano Lectivo: 2017/2018
Duração: 6 meses
Data início: 2018-02-03
Data final: 2018-07-31
Vagas: 1
Podem candidatar-se: L :: Física (2º Ano) (3º Ano)
PERFIL DE COMPETÊNCIAS
Capacidade de trabalho laboratorial; Capacidade de trabalho em grupo; Capacidade de auto aprendizagem;
PLANO DE ESTÁGIO

The Jahn-Teller distortion, being associated with orbital ordering, plays an important role in defining the physical properties of a large number of perovskite oxides, in especial the rare-earth manganites, RMnO3 (R a trivalent rare-earth ion), and so it has been a topic of huge interest, namely in magnetoresistance and multiferroic materials.

In this project, we present a comprehensive experimental work regarding the effect of chemical substitution n the Jahn-Teller distortion in the TbMn1-xFexO3 system ( 0 ≤ x ≤ 1), where the suppression of the cooperative Jahn-Teller distortion is achieved at room conditions, and discuss its effects on the lattice dynamics, through Raman spectroscopy.

The main goals are:

A. to study the correlation between the disappearance of the cooperate Jahn-Teller distortion and the magnetic phase diagram the TbMn1-xFexO3 system;

B. to analyze the spin-lattice coupling, to unravel the vibrational signature of the suppression of the cooperative Jahn-Teller distortion;

C. to understand the mechanisms underlying the disappearance of the cooperative Jahn-Teller distortion in the TbMn1-xFexO3 system and the emergence of magnetic phases, based on symmetry arguments towards the development of a phenomenological Landau model.

The tasks proposed are:

0. to study the relevant published bibliography in order to write a state-of-art of the theme;

1. to record the Raman signal under different fixed temperatures, in order to follow the x-dependence of the Raman active- rotational modes;

2. to record temperature dependent powder XRD patterns to refine the crystal structure at different fixed temperatures, and get information regarding the atomic positions;

3. to analyze the experimental data by using the theoretical models available in the literature and available computational tools to perform symmetry-adapted distortion modes decomposition;

4. to correlate the Jahn-Teller evolution as a function of x and T with the magnetic phase diagram;

5. to analyze the experimental results in the framework of symmetry and coupled order parameters.
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