Eu-based Zintl materials have recently received considerable attention due to their unique properties and application potentials. Herein, we grew $\mathrm{EuA}{\mathrm{l}}_2\mathrm{S}{\mathrm{i}}_2$ single crystals and studied the magnetic susceptibility, magnetoresistance, angular magnetoresistance, and band structures. Magnetic susceptibility and magnetization data establish $\mathrm{EuA}{\mathrm{l}}_2\mathrm{S}{\mathrm{i}}_2$ as an antiferromagnet with short-range ferromagnetic correlations. Its resistivity shows metallic behavior, and well-defined peaks around the Néel temperature, indicative of the presence of magnetic fluctuations. Under magnetic field, the resistivity peak decreases, while the low-temperature resistivity increases, demonstrating respective negative and positive magnetoresistance. An analysis using the Kohler rule and Bethe-ansatz theory reveals that the low- and high-temperature magnetoresistance may result from moderate carrier compensation, and suppressed magnetic fluctuations or reduced hopping energy owing to the increased size of magnetic polarons, respectively. Furthermore, the angular magnetoresistance measurements uncover $\mathrm{EuA}{\mathrm{l}}_2\mathrm{S}{\mathrm{i}}_2$'s moderate electronic anisotropy. Our theoretical studies not only corroborate these results, but also reveal topologically nontrivial band structures that evolve across magnetic phase transitions. These findings demonstrate the crucial role of magnetic orders in determining transport and electronic properties of $\mathrm{EuA}{\mathrm{l}}_2\mathrm{S}{\mathrm{i}}_2$, while establishing the Zintl phase as a promising material platform for exploring emergent quantum phenomena arising from the interplay of magnetism, transport, and topology.

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• Anisotropic magnetoresistance
• Semimetals
• Band structure methods
• Magnetization measurements
• Resistivity measurements