The role of thermal disorder for magnetism and the $\alpha - \gamma$ transition in Cerium; Results from density-functional theory

TL;DR

This study uses density-functional theory to explore how thermal disorder influences magnetism and the alpha-gamma transition in Cerium, highlighting the importance of disorder-induced entropy in phase stability.

Contribution

It demonstrates how thermal disorder affects magnetic moments and phase stability in Cerium, providing insights into the alpha-gamma transition through large-scale DFT calculations.

Findings

Thermal disorder increases magnetic moment fluctuations.

Disorder stabilizes the gamma phase via entropy effects.

Core level spectroscopy can detect disorder effects.

Abstract

The electronic structures of fcc Ce are calculated for large supercells with varying disorder by use of density-functional theory. Thermal disorder induces fluctuations of the amplitude of the magnetic moments and an increase the average moments in the high-volume phase. The ferro-magnetic solutions move towards lower volume than in calculations for the perfectly ordered lattice. Therefore, disorder contributes via entropy to the stabilization of the $\gamma$ phase at high $T$, and it is important for an understanding of the $\alpha-\gamma$ transition. Core level spectroscopy would be a mean to detect disorder through the spread of Madelung shifts and local exchange splittings.