Strongly anisotropic antiferromagnetic coupling in EuFe2As2 revealed by stress detwinning

TL;DR

This study uncovers a strongly anisotropic Eu-Fe magnetic interaction in EuFe2As2, revealing a spin-flip transition driven by stress and magnetic field, highlighting complex magnetostructural coupling in this high-temperature superconductor parent compound.

Contribution

The paper demonstrates a novel method combining stress and magnetic field to isolate Eu-Fe magnetic interactions, revealing a new anisotropic exchange mechanism.

Findings

Identification of a stress-induced spin-flip transition in EuFe2As2.

Evidence of strongly anisotropic Eu-Fe magnetic coupling.

Separation of structural domain detwinning from Eu moment reorientation.

Abstract

Of all parent compounds of iron-based high-temperature superconductors, EuFe2As2 exhibits by far the largest magnetostructural coupling due to the sizable biquadratic interaction between Eu and Fe moments. While the coupling between Eu antiferromagnetic order and Fe structural/antiferromagnetic domains enables rapid field detwinning, this prevents simple magnetometry measurements from extracting the critical fields of the Eu metamagnetic transition. Here we measure these critical fields by combining x-ray magnetic circular dichroism spectroscopy with in-situ tunable uniaxial stress and applied magnetic field. The combination of two tuning knobs allows us to separate the stress-detwinning of structural domains from the field-induced reorientation of Eu moments. Intriguingly, we find a spin-flip transition which can only result from a strongly anisotropic interaction between Eu planes. We argue that this anisotropic exchange is a consequence of the strong anisotropy in the magnetically ordered Fe layer, which presents a new form of higher-order coupling between Eu and Fe magnetism.