Nonrelativistic Multiferroicity in the Nonstoichiometric Spin s=1/2   Spiral Chain Cuprate LiCu2O2
  We argue for a recently observed puzzling multiferroic behavior in s=1/2 1D chain cuprate LiCu2O2 with edge-shared arrangement of CuO4 plaquettes and incommensurate spiral spin ordering can be consistently explained if one takes into account the nonrelativistic exchange-induced electric polarization on the Cu2+ centers substituting for the positions native for the Cu1+ ions. These substituent centers are proved to be an effective probe of the spin incommensurability and magnetic field effects. 
A.S. Moskvin, Yu.D. Panov, and S.-L. Drechsler