Examination of the Anisotropic Spin Exchange Interactions of CuM2O6 (M=Sb, V, Nb) by Spin Dimer Analysis

The anisotropic spin exchange interactions of the magnetic solids CuM2O6 (M=Sb, V, Nb) were explained by analyzing their reported crystal structures and calculating the spin orbital interaction energies of their spin dimers. The magnetic orbital of each Cu2+ site in CuM2O6 is given by the "x2–y2" orbital so that the magnitude of an antiferromagnetic spin exchange interaction for a given spin dimer increases when the arrangement of the nearest-neighbor square-planar CuO4 units containing the magnetic orbitals provides a good sigma overlap between the adjacent magnetic orbitals. The one-dimensional magnetic chains of ALPHACuV2O6, BETA-CuNb2O6, and ALPHA-CuNb2O6 run along a direction different than their edge-sharing CuO4 chain directions. Our study predicts that the antiferromagnetic ordering in BETA-CuNb2O6 should make the magnetic unit cell double the chemical unit cell along the b-direction.