Grüneisen rule in cubic rare-earth cage systems : the examples of LaB\(_6\) and LaPt\(_{4}\)Ge\(_{12}\)

In some intermetallic compounds, the crystallographic structure allows for an unusual latitude of movement of lanthanide ions inside so-called cages. Examples of such magnetic cage systems include the rare-earth hexaborides RB6 and filled skutterudites RPt4Ge12 series. In both instances, the rare-ea...

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Bibliographic Details
Published in:arXiv.org 2024-12
Main Authors: Amara, Mehdi, Opagiste, Christine, Natalya Yu Shitsevalova
Format: Article
Language:English
Subjects:
Cages
Crystal structure
Crystallography
Earth movements
Intermetallic compounds
Low temperature
Magnetic properties
Rare earth elements
Thermal expansion
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Summary:In some intermetallic compounds, the crystallographic structure allows for an unusual latitude of movement of lanthanide ions inside so-called cages. Examples of such magnetic cage systems include the rare-earth hexaborides RB6 and filled skutterudites RPt4Ge12 series. In both instances, the rare-earth site, at the center of the cage, is of high symmetry, which may preserve some degree of orbital degeneracy. A deviation from the cage center lifts this degeneracy, yielding an interplay between the rare-earth movement and the system properties in the paramagnetic range. In particular, the low temperature thermal expansion should reflect this cage-specific crystal field contribution. This study presents an experimental investigation of the thermal expansion in the paramagnetic range of some elements in the aforementioned series. From a simple model for the vibrations in cage systems, a description of the phononic thermal expansion is proposed, within the quasi-harmonic approximation. Accounting for this non-magnetic contributions helps discern the influence of the orbital degeneracy at low temperature.
ISSN:2331-8422