Pressure-Induced Antiferromagnetic Bulk Superconductor EuFe$_2$As$_2$

TL;DR

This paper explores how applying pressure affects the magnetic and superconducting phases of EuFe$_2$As$_2$, revealing an antiferromagnetic phase within the superconducting state and explaining critical field behaviors through exchange interactions.

Contribution

It provides the first detailed phase diagram of EuFe$_2$As$_2$ under pressure, highlighting the coexistence of antiferromagnetism and superconductivity and explaining critical field curvature.

Findings

Antiferromagnetic Eu$^{2+}$ moments are enclosed within the superconducting phase.

Critical field curves show strong concave curvature explained by exchange interactions.

The phase diagram maps magnetic and superconducting states under pressure.

Abstract

We present the magnetic and superconducting phase diagram of EuFe$_2$As$_2$ for $B \parallel c$ and $B \parallel ab$. The antiferromagnetic phase of the Eu$^{2+}$ moments is completely enclosed in the superconducting phase. The upper critical field vs. temperature curves exhibit strong concave curvatures, which can be explained by the Jaccarino-Peter compensation effect due to the antiferromagnetic exchange interaction between the Eu$^{2+}$ moments and conduction electrons.