Superexchange interaction revisited: the role of the A-site cations in ACuO3 (A = Se, Te)

To investigate the effects of A-site cations on the magnetic interaction in highly distorted perovskite ACuO(3) (A = Se, Te), we have set the microscopic Hamiltonian for the Cu-O-Cu-A cluster, taking into account the (s) over barp or (p) over barp hybridization between A-(s) over bar or A-(p) over bar and O-2p orbitals. We have found that (i) the superexchange interaction of the simple Cu-O-Cu triad without considering the A-site effect is inadequate to explain the ferromagnetism of SeCuO3, (ii) the (p) over barp hybridization weakens the superexchange interactions and (iii) the (s) over barp hybridization induces the ferromagnetic superexchange interaction along the c-axis. We have also verified that the (s) over barp hybridization affects the magnetic interaction through anisotropic charge transfer energy shift in the Cu-O-Cu interaction path.