Influence of the Rare Earth Cation on the Magnetic Properties of Layered 12R-Ba₄M⁴⁺Mn₃O₁₂ (M = Ce, Pr) Perovskites

Material design is increasingly used to realize desired functional properties, and the perovskite structure family is one of the richest and most diverse: perovskites are employed in many applications due to their structural flexibility and compositional diversity. Hexagonal, layered perovskite structures with chains of face-sharing transition metal oxide octahedra have attracted great interest as quantum materials due to their magnetic and electronic properties. Ba₄MMn₃O₁₂, a member of the "12R" class of hexagonal, layered perovskites, contains trimers of face-sharing MnO₆ octahedra that are linked by a corner-sharing, bridging MO₆ octahedron. Here, we investigate cluster magnetism in the Mn₃O₁₂ trimers and the role of this bridging octahedron on the magnetic properties of two isostructural 12R materials by systematically changing the M⁴⁺ cation from nonmagnetic Ce⁴⁺ (f⁰) to magnetic Pr⁴⁺ (f¹). We synthesized 12R-Ba₄MMn₃O₁₂ (M= Ce, Pr) with high phase purity and characterized their low-temperature crystal structures and magnetic properties. Using substantially higher purity samples than previously reported, we confirm the frustrated antiferromagnetic ground state of 12R-Ba₄PrMn₃O₁₂ below T_N ≈ 7.75 K and explore the cluster magnetism of its Mn₃O₁₂ trimers. Despite being atomically isostructural with 12R-Ba₄CeMn₃O₁₂, the f¹ electron associated with Pr⁴⁺ causes much more complex magnetic properties in 12R-Ba₄PrMn₃O₁₂. In 12R-Ba₄PrMn₃O₁₂, we observe a sharp, likely antiferromagnetic transition at T₂ ≈ 12.15 K and an additional transition at T₁ ≈ 200 K, likely in canted antiferromagnetic order. These results suggest that careful variation of composition within the family of hexagonal, layered perovskites can be used to tune material properties using the complex role of the Pr⁴⁺ ion in magnetism.