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 Neel temperature.
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