Multiferroicity due to nonstoichiometry in the chain cuprate LiVCuO4

The recently observed multiferroic behavior in the s= 1/2 chain cuprate LiVCuO(4) (equivalent to LiCuVO(4)) with edge-shared CuO(4) plaquettes and helical spin ordering does not agree with the existing theories such as a spin-current scenario. We argue that the effect can be consistently explained, if the exchange-induced electric polarization on the out-of-chain Cu(2+) centers substituting for Li ions in LiVCuO(4) is taken into account. These substituent centers are proved to be an effective probe of the spin incommensurability and the magnetic-field effects. Copyright (c) EPLA, 2008.