A-type antiferromagnetic order in semiconducting EuMg$_2$Sb$_2$ single crystals

TL;DR

This study reveals that EuMg$_2$Sb$_2$ is a semiconducting material with A-type antiferromagnetic order, characterized by a narrow energy gap and specific magnetic alignment, influenced by spin-orbit coupling.

Contribution

The paper provides the first detailed investigation of the electronic and magnetic properties of EuMg$_2$Sb$_2$, including its semiconducting behavior and magnetic structure, using resistivity, ARPES, and neutron diffraction.

Findings

EuMg$_2$Sb$_2$ exhibits semiconducting behavior with a 370 meV energy gap.

The compound orders antiferromagnetically at 8.0 K with A-type magnetic structure.

Eu-moments reorient below $T_N$ due to low in-plane anisotropy.

Abstract

Eu-based Zintl-phase materials EuA$_2$Pn$_2$ (A = Mg, In, Cd, Zn; Pn = Bi, Sb, As, P) have generated significant recent interest owing to the complex interplay of magnetism and band topology. Here, we investigated the electronic, magnetic, and electronic properties of the layered Zintl-phase single crystals of EuMg$_2$Sb$_2$ with the trigonal CaAl$_2$Si$_2$ crystal structure (space group $P\bar{3}m1$). Electrical resistivity measurements complemented with angle-resolved photoemission spectroscopy (ARPES) studies find an activated behavior with the intrinsic conductivity at high temperatures indicating a semiconducting electronic ground state with a narrow energy gap of 370 meV. Magnetic susceptibility and zero-field heat-capacity measurements indicate that the compound undergoes antiferromagnetic (AFM) ordering at the Neel temperature $T_{\rm N}$ = 8.0(2) K. Zero-field neutron-diffraction measurements reveal that the AFM ordering is A-type where the Eu ordered moments (Eu$^{2+}$, S= 7/2) arranged in ab-plane layers are aligned ferromagnetically in the ab plane with the Eu moments in adjacent layers aligned antiferromagnetically. We also find that Eu-moment reorientation in the trigonal AFM domains within the ab planes occurs below $T_{\rm N}$ at low fields < 0.05 T due to very small in-plane anisotropy. Although isostructural semimetallic EuMg$_2$Bi$_2$ is reported to host Dirac surface states, the observation of narrow-gap semiconducting behavior in EuMg$_2$Sb$_2$ implies a strong role of spin-orbit coupling in tuning the electronic states of these materials.