3D to 2D Magnetic Ordering of Fe Oxides Induced by Their Layered Perovskite Structure.

The antiferromagnetic behavior of Fe oxides of composition REBaCaFeO, REBaCaFeO, and REBaCaFeO (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe 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 Fe 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 () of the compounds. The oxides present an interesting transition from three-dimensional (3D) to two-dimensional (2D) magnetic behavior above . The 2D magnetic interactions are stronger within the FeO6 octahedra layers than in the FeO4 tetrahedra layers.