# Visualization of Magnetic Flux Structure in Phosphorus-Doped EuFe$_2$As$_2$ Single Crystals

## TL;DR

This study visualizes magnetic flux and domain structures in phosphorus-doped EuFe$_2$As$_2$ single crystals, revealing vortex and magnetic domain formations across different temperature ranges using advanced microscopy techniques.

## Contribution

It provides the first detailed visualization of magnetic flux and domain structures in phosphorus-doped EuFe$_2$As$_2$ single crystals, highlighting their behavior in superconducting and ferromagnetic phases.

## Key findings

- Vortex structures observed between 17.7 K and 22 K.
- Magnetic domain structures appear below 17.7 K.
- Flux structures are typical for type-II superconductors.

## Abstract

Magnetic flux structure on the surface of EuFe$_2$(As$\rm_{1-x}$P$\rm_x$)$_2$ single crystals with nearly optimal phosphorus doping levels $x=0.20$, and $x=0.21$ is studied by low-temperature magnetic force microscopy and decoration with ferromagnetic nanoparticles. The studies are performed in a broad temperature range. It is shown that the single crystal with $x=0.21$ in the temperature range between the critical temperatures $T_{\rm SC}=22$ K and $T_{\rm C}=17.7$ K of the superconducting and ferromagnetic phase transitions, respectively, has the vortex structure of a frozen magnetic flux, typical for type-II superconductors. The magnetic domain structure is observed in the superconducting state below $T_{\rm C}$. The nature of this structure is discussed.