Microscopic theory of magnetic interactions in KCuF3 and LaMnO3 - The role of charge transfer

We analyze the spin exchange interactions J ab and J c in the A-type antiferromagnetic phase of KCuF 3 and LaMnO 3 . One finds that the quasi one-dimensional spin interactions in KCuF 3 are consistent with the charge-transfer type of insulating state, while the modifications of J ab and J c by the charge-transfer superexchange terms are moderate in the Mott insulator LaMnO 3 . We point out on the example of LaMnO 3 that a reliable determination of the experimental microscopic parameters of spin-orbital models is possible only when results of magnetic and optical experiments can be combined.