  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-ray
magnetic circular dichroism, we have found a very large and a moderate orbital
contribution to the magnetism in alpha- 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 in alpha-CoV2O6 lead to a strong mixture of t2g and eg orbitals
which, via the local atomic Coulomb and exchange interactions, results in an
exceptionally large orbital moment.
