Electrical and magnetic properties of A₂Cu₃O₄X₂ (A = alkaline-earth; X = halogen)

We have investigated electrical and magnetic properties of A₂Cu₃O₄X₂ (A = alkaline-earth; X = halogen) with the Cu₃O₄ plane, which is composed of Cu(1)O₂ and extra Cu(2) sublattices. The electrical resistivity exhibits semiconductive behavior. The magnetic susceptibility shows three-dimensional antiferromagnetic order below T_N(1) and T_N(2) for the Cu(1)O₂ and Cu(2) sublattices, respectively. A broad peak due to the two-dimensional antiferromagnetic order in the Cu(2) sublattice is also observed around T_N^2D(2). With increasing ionic-radii of A and X, the lattice parameters increase, the electrical resistivity increases and values of T_N(1) and T_N^2D(2) decrease. These results are explained as being due to the decrease of the overlap between the Cu 3d orbit and the O 2p, X p ones.