Competition of local-moment ferromagnetism and superconductivity in Co-substituted EuFe2As2

TL;DR

This paper investigates how pressure-induced superconductivity interacts with Eu2+ magnetic order in EuFe1.9Co0.1As2, revealing that superconductivity is suppressed when magnetic ordering temperature exceeds the superconducting onset temperature.

Contribution

It provides new insights into the competition between local-moment ferromagnetism and superconductivity in EuFe2As2-based compounds under pressure.

Findings

Superconductivity is suppressed when Eu2+ magnetic ordering temperature exceeds the superconducting onset temperature.

Pressure tuning allows control over the balance between magnetic order and superconductivity.

EuFe1.9Co0.1As2 exhibits re-entrant behavior due to the interplay of magnetism and superconductivity.

Abstract

In contrast to SrFe2As2, where only the iron possesses a magnetic moment, in EuFe2As2 an additional large, local magnetic moment is carried by Eu2+. Like SrFe2As2, EuFe2As2 exhibits a spin-density wave transition at high temperatures, but in addition the magnetic moments of the Eu2+ order at around 20 K. The interplay of pressure-induced superconductivity and the Eu2+ order leads to a behavior which is reminiscent of re-entrant superconductivity as it was observed, for example, in the ternary Chevrel phases or in the rare-earth nickel borocarbides. Here, we study the delicate interplay of the ordering of the Eu2+ moments and superconductivity in EuFe1.9Co0.1As2, where application of external pressure makes it possible to sensitively tune the ratio of the magnetic (T_C) and the superconducting (T_{c,onset}) critical temperatures. We find that superconductivity disappears once T_C > T_{c,onset}.