Interplay between magnetism and superconductivity in EuFe(2-x)Co(x)As2 studied by 57Fe and 151Eu M\"{o}ssbauer spectroscopy

TL;DR

This study investigates how Co substitution affects magnetism and superconductivity in EuFe(2-x)Co(x)As2 using Mössbauer spectroscopy, revealing coexistence of superconductivity with magnetic order and the suppression of spin density wave.

Contribution

It provides detailed insights into the interplay between magnetism and superconductivity in EuFe(2-x)Co(x)As2, highlighting the coexistence and magnetic re-orientation phenomena.

Findings

Spin density wave is suppressed but persists in superconducting regions.

Superconductivity coexists with Eu magnetic order within the same volume.

Superconductivity appears filamentary and confined to non-magnetic components.

Abstract

The compound EuFe(2-x)Co(x)As2 was investigated by means of the 57Fe and 151Eu Moessbauer spectroscopy versus temperature (4.2 - 300 K) for x=0 (parent), x=0.34 - 0.39 (superconductor) and x=0.58 (overdoped). It was found that spin density wave (SDW) is suppressed by Co-substitution, however it survives in the region of superconductivity, but iron spectra exhibit some non-magnetic component in the superconducting region. Europium orders anti-ferromagnetically regardless of the Co concentration with the spin re-orientation from the a-axis in the parent compound toward c-axis with the increasing replacement of iron by cobalt. The re-orientation takes place close to the a-c plane. Some trivalent europium appears in EuFe(2-x)Co(x)As2 versus substitution due to the chemical pressure induced by Co-atoms and it experiences some transferred hyperfine field from Eu2+. Iron experiences some transferred field due to the europium ordering for substituted samples in the SDW and non-magnetic state both, while the transferred field is undetectable in the parent compound. Superconductivity coexists with the 4f-europium magnetic order within the same volume. It seems that superconductivity has some filamentary character in EuFe(2-x)Co(x)As2 and it is confined to the non-magnetic component seen by the iron Moessbauer spectroscopy.