Dual Character of Magnetism in Ferropnictides: Insights from Optical Measurements

TL;DR

This study combines optical spectroscopy and first-principles calculations to reveal the dual nature of magnetism in EuFe₂As₂, showing it exhibits both local and itinerant magnetic characteristics through distinct electronic gap features.

Contribution

It provides new insights into the mixed local-itinerant magnetic behavior in ferropnictides by identifying two different gap-like features and their origins.

Findings

Observation of two gap-like features with different behaviors.

Identification of these features with specific electronic band transitions.

Demonstration that magnetism in ferropnictides is neither fully local nor itinerant.

Abstract

We investigate the electronic structure of EuFe$_{2}$As$_{2}$ using optical spectroscopy and first-principles calculations. At low temperature we observe the evolution of \textit{two} gap-like features, one having a BCS mean-field behavior and another with strongly non-BCS behavior. Using band structure calculations, we identify the former with a spin-Peierls-like partial gap in $d_{yz}$ bands, and the latter with the transition across the large exchange gap in $d_{xz}/d_{xy}$ bands. Our results demonstrate that the antiferromagnetism in the ferropnictides is neither fully local nor fully itinerant, but contains elements of both.