Evidence for local structural symmetry-breaking in Ca$_{1-x}$Eu$_{x}$B$_{6}$

TL;DR

This study provides the first experimental evidence of local symmetry-breaking in Ca$_{1-x}$Eu$_{x}$B$_{6}$, revealing tetragonal distortions in boron octahedra that could explain ferromagnetism in Eu-hexaborides.

Contribution

It demonstrates local symmetry-breaking in Ca$_{1-x}$Eu$_{x}$B$_{6}$ using Raman scattering, a novel insight into the material's structural properties.

Findings

Evidence of local tetragonal symmetry in boron octahedra

Correlation between symmetry-breaking and ferromagnetism

First experimental detection of local structural distortions

Abstract

In this work we present a systematic Raman Scattering study in the Ca$_{1-x}$% Eu$_{x}$B$_{6}$ series ($0.00\leqslant x\leqslant 1.00$). Our results are the first experimental evidence for the occurrence of a local symmetry break of the crystalline structure in this system. The local symmetry of some Boron octahedra is tetragonal instead of cubic. This result may explain the appearance of ferromagnetism in Eu-hexaborades since magnetic ordering is forbidden in the $O_{h}$ space group of this system.