Antiferromagnetic domains in a single crystal of the A-type spin-7/2 trigonal topological insulator EuSn${}_2$As${}_2$

EuSn${}_2$As${}_2$ is a trigonal A-type antiferromagnetic topological insulator with the moments aligned in the $ab$ plane and with a Néel temperature $T_{\mathrm{N}}=23.5$ K. Here we report that an EuSn${}_2$As${}_2$ crystal exhibits a broad peak at $H_{\mathrm{c}1}=1100$ Oe in the field derivative $d{M}_{ab}\mathrm{/}dH$ of the $ab$-plane magnetization $M_{ab}(H)$ at temperature $T=2$ K, demonstrating the presence of trigonal antiferromagnetic domains. We model these $M_{ab}(H,T=2\mathrm{K})$ data and obtain the trigonal anisotropy-energy coefficient $K_3$ that is 13.3 and 3.7 times larger than those we previously reported for single crystals of the trigonal compounds EuMg${}_2$Sb${}_2$ and EuMg${}_2$Bi${}_2$, respectively.