Magnetic topological materials are a class of compounds which can host massless electrons controlled by the magnetic order. One such compound is ${\mathrm{EuZn}}_2{\mathrm{Sb}}_2$, which has recently garnered interest due to its strong interplay between the Eu magnetism and charge carriers. However, the topology of the electronic band structure, which depends on the ground state magnetic configuration of the europium sublattice, has not been determined. Based on our ab initio calculations, we find that an in-plane and out-of-plane $A$-type antiferromagnetic (AFM) order generates a topological crystalline insulator and Dirac semimetal, respectively, whereas a ferromagnetic (FM) order stabilizes a Weyl semimetal. Our resonant x-ray elastic scattering measurements of single-crystal thin-film ${\mathrm{EuZn}}_2{\mathrm{Sb}}_2$ reveal both a sharp magnetic peak at $\mathit{Q}=\left(0,0,\frac{1}{2}\right)$ and broad $\mathit{Q}=(0,0,1)$ below $T_{\mathrm{N}}=12.9\mathrm{K}$, which is associated with an $A$-type AFM and FM order, respectively. Our measurements indicate that the FM and AFM layers are spatially separated along the crystal $c$ axis, with the former limited to the top three atomic layers. We propose that ${\mathrm{EuZn}}_2{\mathrm{Sb}}_2$ behaves as a Weyl semimetal in the surface FM layers, and as a topological crystalline insulator in the lower AFM layers.

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• Magnetic thin films
• Topological materials
• DFT+U
• X-ray resonant magnetic scattering