A Eu-Based Zintl Compound Eu ₉ Zn _4.5 As ₉ with Multiple Magnetic Transitions

Single crystals of a Eu-based Zintl compound, Eu 9 Zn 4.5 As 9, were synthesized by a flux method and characterized by single-crystal X-ray diffraction, magnetic measurements, heat capacity, and electrical transport. Eu 9 Zn 4.5 As 9 crystallizes in an orthorhombic structure (space group Pnma ) composed of a highly complex Zn–As polyanionic framework featuring multiple types of Zn coordination and partially occupied Zn sites. The presence of partially occupied Zn sites leads to deviations from ideal Zintl electron counting, resulting in metallic electrical transport. Magnetic susceptibility, isothermal magnetization, and heat capacity measurements reveal multiple magnetic transitions at low temperatures, including the development of a short-range ferromagnetic order below ∼15 K, a long-range antiferromagnetic transition at 11.3 K, and a further transition into a canted antiferromagnetic state at 6.8 K. In addition, a negative magnetoresistance of up to −40% is observed at low temperatures, reflecting a strong coupling between the Eu 2+ moments and the itinerant charge carriers. These results demonstrate that Eu 9 Zn 4.5 As 9 is a metallic Zintl compound with a structurally complex polyanionic framework and rich magnetic behaviors.