Pressure-induced changes in the magnetic and valence state of EuFe2As2

TL;DR

This study investigates how applying pressure to EuFe2As2 alters its magnetic and valence states, revealing suppression of antiferromagnetism, emergence of superconductivity near a critical pressure, and a Eu valence change at higher pressures.

Contribution

It provides new insights into pressure-induced magnetic and valence transitions in EuFe2As2, combining multiple experimental techniques to map phase changes.

Findings

Antiferromagnetism suppressed near 2.5-2.7 GPa.

Re-entrant superconductivity appears near critical pressure.

Eu valence changes from Eu2+ to Eu3+ at pressures above 6 GPa.

Abstract

We present the results of electrical resistivity, ac specific heat, magnetic susceptibility, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under pressure. Applying pressure leads to a continuous suppression of the antiferromagnetism associated with Fe moments and the antiferromagnetic transition temperature becomes zero in the vicinity of a critical pressure Pc ~2.5-2.7 GPa. Pressure-induced re-entrant superconductivity, which is highly sensitive to the homogeneity of the pressure, only appears in the narrow pressure region in the vicinity of Pc due to the competition between superconductivity and the antiferromagnetic ordering of Eu2+ moments. The antiferromagnetic state of Eu2+ moments changes to the ferromagnetic state above 6 GPa. We also found that the ferromagnetic order is suppressed with further increasing pressure, which is connected with a valence change of Eu ions.