# Local and collective magnetism of EuFe$_2$As$_2$

## TL;DR

This study investigates the local and collective magnetic properties of EuFe₂As₂, revealing that Eu's high magnetic moment has minimal impact on Fe magnetism and spin excitations, aligning with behaviors seen in similar parent compounds.

## Contribution

It provides detailed experimental insights into how Eu's magnetic ordering influences Fe magnetism and excitations in EuFe₂As₂, a key parent compound in iron-based superconductors.

## Key findings

- EuFe₂As₂ has a local Fe magnetic moment of ~1.3-1.45 μ_B.
- Dispersive magnetic excitations with bandwidth ~170-180 meV observed.
- Eu's high magnetic moment has limited effect on Fe magnetism.

## Abstract

We present an experimental study of the local and collective magnetism of $\mathrm{EuFe_2As_2}$, that is isostructural with the high temperature superconductor parent compound $\mathrm{BaFe_2As_2}$. In contrast to $\mathrm{BaFe_2As_2}$, where only Fe spins order, $\mathrm{EuFe_2As_2}$ has an additional magnetic transition below 20 K due to the ordering of the Eu$^{2+}$ spins ($J =7/2$, with $L=0$ and $S=7/2$) in an A-type antiferromagnetic texture (ferromagnetic layers stacked antiferromagnetically). This may potentially affect the FeAs layer and its local and correlated magnetism. Fe-K$_\beta$ x-ray emission experiments on $\mathrm{EuFe_2As_2}$ single crystals reveal a local magnetic moment of 1.3$\pm0.15~\mu_B$ at 15 K that slightly increases to 1.45$\pm0.15~\mu_B$ at 300 K. Resonant inelastic x-ray scattering (RIXS) experiments performed on the same crystals show dispersive broad (in energy) magnetic excitations along $\mathrm{(0, 0)\rightarrow(1, 0)}$ and $\mathrm{(0, 0)\rightarrow(1, 1)}$ with a bandwidth on the order of 170-180 meV. These results on local and collective magnetism are in line with other parent compounds of the $\mathrm{AFe_2As_2}$ series ($A=$ Ba, Ca, and Sr), especially the well characterized $\mathrm{BaFe_2As_2}$. Thus, our experiments lead us to the conclusion that the effect of the high magnetic moment of Eu on the magnitude of both Fe local magnetic moment and spin excitations is small and confined to low energy excitations.