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

Abstract

Eu-based Zintl-phase materials EuA2P n2 (A = Mg, In, Cd, Zn; P n = 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 EuMg2Sb2 with the trigonal CaAl2Si2 crystal structure (space group P 3m1). 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 Néel temperature TN = 8.0(2) K. Zero-field neutrondiffraction 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 below TN at low fields < 0.05 T due to very small in-plane anisotropy. Although isostructural semimetallic EuMg2Bi2 is reported to host Dirac surface states, the observation of narrow-gap semiconducting behavior in EuMg2Sb2 implies a strong role of spin-orbit coupling in tuning the electronic states of these materials.