3D to 2D Magnetic Ordering of Fe³⁺ Oxides Induced by Their Layered Perovskite Structure

The antiferromagnetic behavior of Fe³⁺ oxides of composition RE_1.2Ba_1.2Ca_0.6Fe₃O₈, RE_2.2Ba_3.2Ca_2.6Fe₈O₂₁, and REBa₂Ca₂Fe₅O₁₃ (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe³⁺ cations and their ordering, which is coupled with the layered RE/Ba/Ca arrangement within the perovskite-related structure. Determination of the magnetic structures reveals different magnetic moments associated with Fe³⁺ spins in the different oxygen polyhedra (octahedron, tetrahedron, and square pyramid). The structural aspects impact on the strength of the Fe-O-Fe superexchange interactions and, therefore, on the Néel temperature (T_N) of the compounds. The oxides present an interesting transition from three-dimensional (3D) to two-dimensional (2D) magnetic behavior above T_N. The 2D magnetic interactions are stronger within the FeO6 octahedra layers than in the FeO4 tetrahedra layers.