Correlation between intercalated magnetic layers and superconductivity in pressurized EuFe2(As0.81P0.19)2

TL;DR

This study investigates how intercalated magnetic layers influence superconductivity in EuFe2(As0.81P0.19)2 under high pressure, revealing a complex interplay between magnetic order, Eu valence, and superconductivity.

Contribution

It provides new insights into the pressure-induced magnetic and electronic phase transitions in EuFe2(As0.81P0.19)2, highlighting the role of Eu valence in superconductivity suppression.

Findings

Unconfirmed magnetic order coexists with superconductivity at low pressure.

Magnetic order converts to ferromagnetic state above 0.5 GPa, where superconductivity disappears.

Eu valence increases under pressure, affecting magnetic and superconducting states.

Abstract

We report comprehensive high pressure studies on correlation between intercalated magnetic layers and superconductivity in EuFe2(As0.81P0.19)2 single crystal through in-situ high pressure resistance, specific heat, X-ray diffraction and X-ray absorption measurements. We find that an unconfirmed magnetic order of the intercalated layers coexists with superconductivity in a narrow pressure range 0-0.5GPa, and then it converts to a ferromagnetic (FM) order at pressure above 0.5 GPa, where its superconductivity is absent. The obtained temperature-pressure phase diagram clearly demonstrates that the unconfirmed magnetic order can emerge from the superconducting state. In stark contrast, the superconductivity cannot develop from the FM state that is evolved from the unconfirmed magnetic state. High pressure X-ray absorption (XAS) measurements reveal that the pressure-induced enhancement of Eu's mean valence plays an important role in suppressing the superconductivity and tuning the transition from the unconfirmed magnetic state to a FM state. The unusual interplay among valence state of Eu ions, magnetism and superconductivity under pressure may shed new light on understanding the role of the intercalated magnetic layers in Fe-based superconductors.