# Reentrant phases in electron-doped $\text{EuFe}_2\text{As}_2$: spin glass and superconductivity

## TL;DR

This study uncovers a reentrant spin glass phase in electron-doped EuFe2As2, revealing complex magnetic transitions and their impact on superconductivity through optical and magnetic measurements.

## Contribution

It provides new experimental evidence of the coexistence and interplay of spin glass behavior and superconductivity in electron-doped EuFe2As2.

## Key findings

- Identification of a reentrant spin glass phase below T_c
- Observation of magnetic transitions at 17 K and 19 K
- Evidence of an additional transition below the spin glass temperature

## Abstract

We report evidence for a reentrant spin glass phase in electron-doped $\text{EuFe}_2\text{As}_2$ single crystals and first traces of the superconductivity re-entrance in optics. In the close-to-optimal doped $\text{Eu}(\text{Fe}_{0.91}\text{Ir}_{0.09})_2\text{As}_2$ and $\text{Eu}(\text{Fe}_{0.93}\text{Rh}_{0.07})_2\text{As}_2$ samples two magnetic transitions are observed below the superconducting critical temperature $T_c \approx 21$~K: the canted $A$-type antiferromagnetic order of the $\text{Eu}^{2+}$ ions sets in around $17\,\text{K}$; the spin glass behavior occurs another $2\,\text{K}$ lower in temperature. In addition, strong evidence for an additional transition is found far below the spin glass temperature. Our extensive optical and magnetic investigations provide new insight into the interplay of local magnetism and superconductivity in these systems and elucidate the effect of the spin-glass phase on the reentrant superconducting state.