Antiferromagnetic perovskites structure

The structure of KCrF3 is derived from the perovskite structure by a tetragonal distortion4. An antiferrodistortive coupling occurs between half-filled dz orbitals and empty d 2 yj orbitals. The superexchange interaction d°z y2 - p - dz2 leads to ferromagnetic layers, antiferromagnetically bound via the empty dx2 y2 orbitals. 

A perovskite-structure system, KNiFs, which does form a multiplet structure and is an antiferromagnetic insulator, was treated by Mattheiss (1972b) in the same way other perovskites were treated he obtained the parameters for this system also, using an LCAO fit. The interatomic matrix elements he obtained,... 

Figure 17 Magnetic structures for antiferromagnetic perovskites. The open and solid black spheres represent sublattices of opposing spin...

The manganates have the layered perovskite structure similar to that found in the YBCO superconductor (see Section 7.16). This similarity is particularly interesting and may lead to increased understanding of both types of material. The nature of the interactions in the manganites is complicated. They show a metal-insulator transition and a ferromagnetic-antiferromagnetic transition associated with CMR. 

In the lanthanide RAIO3 aluminates and RC0O3 orthocobaltites (where Co " is diamagnetic) with a deformed perovskite structure there is a strong competition between the antiferromagnetic exchange and dipolar interactions due to the close packing of the... 

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