# Spin reorientation of the Fe moments in Eu$_{0.5}$Ca$_{0.5}$Fe$_{2}$As$_{2}$: Evidence for a strong interplay of Eu and Fe magnetism

## TL;DR

This study reveals a strong interaction between Eu and Fe magnetic moments in Eu$_{0.5}$Ca$_{0.5}$Fe$_{2}$As$_{2}$, showing a spin reorientation of Fe moments linked to Eu magnetic ordering, using neutron diffraction techniques.

## Contribution

First detailed investigation of magnetic structure and spin reorientation in Eu$_{0.5}$Ca$_{0.5}$Fe$_{2}$As$_{2}$ highlighting Eu-Fe magnetic interplay.

## Key findings

- Eu sublattice remains long-range ordered below 10 K.
- Fe moments exhibit a spin-density-wave transition at 192 K.
- Fe moments reorient into a canted AFM structure at 2.5 K.

## Abstract

Using complementary polarized and unpolarized single-crystal neutron diffraction, we have investigated the temperature-dependent magnetic structures of Eu$_{0.5}$Ca$_{0.5}$Fe$_{2}$As$_{2}$. Upon 50 \% dilution of the Eu sites with isovalent Ca$^{2+}$, the Eu sublattice is found to be still long-range ordered below $\mathit{T_{Eu}}$ = 10 K, in the A-typed antiferromagnetic (AFM) structure. The moment size of Eu$^{2+}$ spins is estimated to be as large as 6.74(4) $\mu_{B}$ at 2.5 K. The Fe sublattice undergoes a spin-density-wave transition at $\mathit{T_{SDW}}$ = 192(2) K and displays an in-plane AFM structure above $\mathit{T_{Eu}}$. However, at 2.5 K, the Fe$^{2+}$ moments are found to be ordered in a canted AFM structure with a canting angle of 14(4){\deg} out of the $\mathit{ab}$ plane. The spin reorientation of Fe below the AFM ordering temperature of Eu provides a direct evidence of a strong interplay between the two magnetic sublattices in Eu$_{0.5}$Ca$_{0.5}$Fe$_{2}$As$_{2}$.