Crystal Defect Doping on Antiferromagnetic Topological Insulator Candidate EuMg₂Bi₂

Here, we report defect doping from partial substitution doping on the magnetic Eu²⁺ site with the nonmagnetic alkaline-earth metal Ca²⁺ in the magnetic topological candidate EuMg₂Bi₂. Resultantly, two new phases Eu_0.50(5)Ca_0.50Mg₂Bi₂ and Eu_0.33(2)Ca_0.67Mg₂Bi₂ were discovered, and the magnetic and electrical measurements were performed and analyzed. A ferromagnetic behavior is realized with increased Ca-doping for Eu_0.33Ca_0.67Mg₂Bi₂, while Eu_0.50Ca_0.50Mg₂Bi₂ remains antiferromagnetic with a significantly lower transition temperature compared to EuMg₂Bi₂. Consequently, the electrical properties of Eu_0.33Ca_0.67Mg₂Bi₂, displaying a semimetallic behavior with negative magnetoresistance, closely resemble those of EuMg₂Bi₂. However, factors including the fluctuating Eu site defects and magnetic fields strongly influence the resistivity of Eu_0.50Ca_0.50Mg₂Bi₂ leading to a large positive magnetoresistance and a semimetal-to-semiconductor transition. Ultimately, these results suggest that EuMg₂Bi₂ could be a tunable platform to study the surface states in antiferromagnetic topological insulators.