Effect of antifluorite layer on the magnetic order in Eu-based 1111 compounds, EuTAsF (T = Zn, Mn, and Fe)

TL;DR

This study investigates how the type of antifluorite layer influences the magnetic order of Eu2+ in EuTAsF compounds, revealing different magnetic structures and interactions depending on the T element.

Contribution

It provides new insights into the magnetic ordering in EuTAsF compounds, combining neutron diffraction and DFT calculations to understand the role of the antifluorite layer's nature.

Findings

EuTAsF compounds exhibit antiferromagnetic transitions around 2.4-3 K.

Different magnetic order patterns are observed depending on T: stripe order for T=Zn, Mn; incommensurate cycloid for T=Fe.

Interplane interactions are significant and influence the magnetic structure, especially in metallic EuFeAsF.

Abstract

The 1111 compounds with an alternating sequence of fluorite and antifluorite layers serve as structural hosts for the vast family of Fe-based superconductors. Here, we use neutron powder diffraction and density-functional-theory (DFT) band-structure calculations to study magnetic order of Eu2+ in the [EuF]+ fluorite layers depending on the nature of the [TAs]- antifluorite layer that can be non-magnetic semiconducting (T = Zn), magnetic semiconducting (T = Mn), or magnetic metallic (T = Fe). Antiferromagnetic transitions at TN ~ 2.4 - 3 K due to an ordering of the Eu2+ magnetic moments were confirmed in all three EuTAsF compounds. Whereas in EuTAsF (T = Zn and Mn), the commensurate k1 = (1/2 1/2 0) stripe order pattern with magnetic moments within the ab-plane is observed, the order in EuFeAsF is incommensurate with k = (0 0.961(1) 1/2) and represents a cycloid of Eu2+ magnetic moments confined within the bc-plane. Additionally, the Mn2+ sublattice in EuMnAsF features a robust G-type antiferromagnetic order that persists at least up to room temperature, with magnetic moments along the c-direction. Although DFT calculations suggest stripe antiferromagnetic order in the Fe-sublattice of EuFeAsF as the ground state, neutron diffraction reveals no evidence of long-range magnetic order associated with Fe. We show that the frustrating interplane interaction J3 between the adjacent [EuF]+ layers is comparable with in-plane J1-J2 interactions already in the case of semiconducting fluorite layers [TAs]- (T = Zn and Mn) and becomes dominant in the case of the metallic [FeAs]- ones. The latter, along with a slight orthorhombic distortion, is proposed to be the origin of the incommensurate magnetic structure observed in EuFeAsF.