Spectroscopic Evidence For Exceptionally High Orbital Moment Induced By Local Distortions In Alpha-Cov2o6

We present a combined experimental and theoretical study on the local magnetism of the Co ions in the spin-chain compound CoV2O6, which crystallizes in two different allotropic phases, alpha- and gamma- CoV2O6. Using x-raymagnetic circular dichroism, we have found an exceptionally high and a moderate orbital contribution to the magnetism in alpha-CoV2O6 and gamma-CoV2O6, respectively. Full-multiplet calculations indicate that the differences in the magnetic behavior of alpha- and gamma-CoV2O6 phases originate from different local distortions of the CoO6 octahedra. In particular, the strong compression of the CoO6 octahedra together with the unusually small octahedral crystal field splitting in alpha-CoV2O6 lead to a strong mixture of t(2g) and e(g) orbitals which, via the local atomic Coulomb and exchange interactions, results in an exceptionally large orbital moment.