Phase diagram of superconductivity and antiferromagnetism in single crystals of Sr(Fe1-xCox)2As2 and Sr1-yEuy(Fe0.88Co0.12)2As2

TL;DR

This study explores the phase diagram of superconductivity and antiferromagnetism in Sr(Fe1-xCox)2As2 and Sr1-yEuy(Fe0.88Co0.12)2As2 single crystals, revealing how magnetic doping influences the coexistence and competition of these states.

Contribution

It provides the first detailed phase diagram showing the interplay between superconductivity and local magnetic moments in these iron arsenide compounds.

Findings

Superconductivity peaks at x ~ 0.12 Co doping in Sr(Fe1-xCox)2As2.

Eu2+ doping suppresses superconductivity and induces antiferromagnetic order.

Superconductivity abruptly disappears when Eu2+ antiferromagnetic order dominates.

Abstract

We report magnetic susceptibility, resistivity and heat capacity measurements on single crystals of the Sr(Fe1-xCox)2As2 and Sr1-yEuy(Fe0.88Co0.12)2As2 series. The optimal Co concentration for superconductivity in Sr(Fe1-xCox)2As2 is determined to be x ~ 0.12. Based on this we grew members of the Sr1-yEuy(Fe0.88Co0.12)2As2 series so as to examine the effects of well defined, local magnetic moments, on the superconducting state. We show that superconductivity is gradually suppressed by paramagnetic Eu2+ doping and coexists with antiferromagnetic ordering of Eu2+ as long as Tc > TN. For y >= 0.65, TN crosses Tc and the superconducting ground state (as manifested by zero resistivity) abruptly disappears with evidence for competition between superconductivity and local moment antiferromagnetism for y up to 0.72. It is speculated that the suppression of the antiferromagnetic fluctuations of Fe sublattice by coupling to the long range order of Eu2+ sublattice destroys bulk superconductivity when TN > Tc.