- Jiří Prchal: Structural changes in magnetics
- 16. 11. 2016, 14:30
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
Intermetallic compounds in many cases evince structural changes in their crystal lattices when the thermodynamic conditions are changed. Especially because of interesting magnetic behavior, specific groups of intermetallics are subject of thorough studies and the structural properties are very often estimated as a side effect during the quality characterization process of the prepared samples prior the study of their magnetic properties. There are three possible scenarios with respect to a relation between the structural changes and magnetic behavior of the material. First (a) if the relation between magnetic and structural transition is not directly observable. The temperatures of the magnetic and structural transition are distant and the magnetic behavior is not affected (although not necessarily) by a potential structural transition in these systems. Or (b) the structural transition leads to the magnetic changes in the material. Also in such case the temperatures of the structural and magnetic transition do not necessarily coincide with each other. In the third situation (c) the crystallographic changes are a consequence of the magnetic ordering or the magnetic easy-axis reorientation.
In the presentation, a focus will be given to the first case (a) which is generally the least intetesting one but in our particular family of compounds several important aspects are worthy to deal with.
The presentation will be focused on the RTX compounds (R=rare-earth metal, T=transition element, X=p-element) adopting the hexagonal ZrNiAl-type of structure because of the mentioned interest in their magnetic behavior. Besides the magnetic study, an abrupt change in the evolution of the crystal structure parameters was found, characterized by a non-ability to reach a specific combinations of the lattice constants a and c.
Although it was found that the structural discontinuity is not a typical phase transition from point of view of the Landau theory of phase transitions, one can register a cardinal impact on the mechanical properties of the prepared samples possessing this structural “transition” which will be described in more detail. We will also present an overview of known hexagonal ZrNiAl-type systems and a discovered systematic evolution of the structural transition upon variation of temperature, composition and hydrostatic-pressure application. Connection with changes in magnetic behavior will be commented as well.