Zero-field magnetic ground state of EuMg2Bi2

Layered trigonal ${\mathrm{EuMg}}_{2}{\mathrm{Bi}}_{2}$ 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 $\ensuremath{\chi}(T)$ of ${\mathrm{EuMg}}_{2}{\mathrm{Bi}}_{2}$ that show the intraplane ordering is ferromagnetic (${\mathrm{Eu}}^{2+},\phantom{\rule{0.16em}{0ex}}S=7/2$) with the moments aligned in the $ab$ plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the N\'eel temperature.