Lack of superconductivity in the phase diagram of single-crystalline Eu(Fe1-xCox)2As2 grown by transition metal arsenide flux

TL;DR

This study re-examines the phase diagram of Eu(Fe1-xCox)2As2 grown by TMA flux and finds no evidence of superconductivity across the doping range, contrasting with some previous reports.

Contribution

It provides a detailed phase diagram for TMA-flux-grown Eu(Fe1-xCox)2As2, showing the absence of superconductivity and clarifying the effects of Co doping on magnetic order.

Findings

Lattice parameter c shrinks linearly with Co doping.

Fe SDW order is suppressed at x > 0.08.

No superconductivity observed in the studied range.

Abstract

The interplay of magnetism and superconductivity (SC) has been a focus of interest in condensed matter physics for decades. EuFe2As2 has been identified as a potential platform to investigate interactions between structural, magnetic, electronic effects as well as coexistence of magnetism and SC with similar transition temperatures. However, there are obvious inconsistencies in the reported phase diagrams of Eu(Fe1-xCox)2As2 crystals grown by different methods. For transition metal arsenide (TMA)-flux-grown crystals, even the existence of SC is open for dispute. Here we re-examine the phase diagram of single-crystalline Eu(Fe1-xCox)2As2 grown by TMA flux. We found that the lattice parameter c shrinks linearly with Co doping, almost twice as fast as that of the tin-flux-grown crystals. With Co doping, the spin-density-wave (SDW) order of Fe sublattice is quickly suppressed, being detected only up to x = 0.08. The magnetic ordering temperature of the Eu2+ sublattice (TEu) shows a systematic evolution with Co doping, first going down and reaching a minimum at x = 0.08, then increasing continuously up to x = 0.24. Over the whole composition range investigated, no signature of SC is observed.