Title: Local and collective magnetism of EuFe$_2$As$_2$,
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.