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

The antiferromagnetic behavior of Fe 3+ oxides of composition RE 1.2 Ba 1.2 Ca 0.6 Fe 3 O 8 , RE 2.2 Ba 3.2 Ca 2.6 Fe 8 O 21 , and REBa 2 Ca 2 Fe 5 O 13 (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe 3+ 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 3+ 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.