Zero-field magnetic ground state of EuMg$_2$Bi$_2$

TL;DR

This study reveals that EuMg$_2$Bi$_2$ exhibits A-type antiferromagnetic order with in-plane ferromagnetic layers below the Néel temperature, providing insights into its magnetic ground state relevant for topological properties.

Contribution

First detailed neutron diffraction and magnetic susceptibility study establishing the zero-field magnetic ground state of EuMg$_2$Bi$_2$ as A-type antiferromagnetic order.

Findings

Intraplane Eu$^{2+}$ moments are ferromagnetically aligned in the $ab$-plane.

Adjacent layers are antiferromagnetically aligned.

Magnetic order sets in below the Néel temperature.

Abstract

Layered trigonal EuMg$_2$Bi$_2$ is reported to be a topological semimetal that hosts multiple Dirac points that may be gapped or split by the onset of magnetic order. Here, we report zero-field single-crystal neutron-diffraction and bulk magnetic susceptibility measurements versus temperature $\chi(T)$ of EuMg$_2$Bi$_2$ that show the intraplane ordering is ferromagnetic (Eu$^{2+},\, S= 7/2$) with the moments aligned in the $ab$-plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the N\'eel temperature.