[Todos] Seminarios DQIAyQF INQUIMAE/ Miercoles 1 de Noviembre, 13h

[sara elizabeth bari]

Seminarios del Dpto. de Química Inorgánica, Analítica y Química Física / INQUIMAE

FCEyN - Universidad de Buenos Aires

http://www.qi.fcen.uba.ar/es

 

2do. Cuatrimestre, 2006

 

 

  

Miercoles 1 de Noviembre, 13.00h
Aula Seminarios, DQIAyQF- INQUIMAE

Ciudad Universitaria, Pab. II, Piso 3

 

Octavio Peña

Equipe Chimie du Solide et Matériaux. Unité de Sciences Chimiques de Rennes

UMR - CNRS 6226. Université de Rennes 1. France

 

Magnetic interactions in manganese mixed-valence materials: from oxide perovskites to sulfide spinels

 

 

Existence of two magnetic sublattices in a well-defined crystalline structure may lead to interesting cooperative phenomena. Basic mechanisms are double-exchange and super-exchange magnetic interactions, in which the role of the ligands (e.g., oxygen anions) is fundamental. These cooperative phenomena may be coupled to electrical conduction, leading to magneto-resistance effects, double phase transitions or coexisting phenomena (e.g., ferromagnetism and superconductivity).

 

In recent years we have been involved with the study of transition-metal oxides of perovskite and spinel structures, our main goal being the modification of the magnetic interactions through subtle changes in the mixed-valence state of the constituents. We will present several examples of our recent work: rare-earth manganites REMnO3 in which the oxidation state of manganese can be modulated either by substitutions at the rare-earth site or by modifying the environment of the transition-metal network ; double and triple oxides derived from the spinel compound NiMn2O4 and their solid solutions (NiMn2-xMexO4) or (Co,Ni,Mn)3O4 ; thiospinels obtained by modifications at the anionic site (oxygen by sulfur).

 

A phenomenological model of two interacting sublattices with antiferromagnetic exchange will be used to explain the spin reversal found in gadolinium-based perovskites. Spin-flop mechanisms will be discussed in the case of erbium perovskites. Finally, the ferrimagnetic properties of the oxide and sulfide spinels will be shown and compared in detail.

 

 

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